Biology In Context Module 1

ECOSYSTEMS1Common plants and animals have many interesting adaptations, and many relationships among organisms can be studied in a local environment.

Context

Cicada shedding its skin

ADAPTATIONSTake a look at yourself; you are a well-adapted organism. You have jointed legs, which allow you to move, to walk, to leap and to run. Consider your hands. They are marvellous instruments capable of delicate work, manipulating objects, grasping, catching and turning. You have adaptations that help you to keep warm. You shiver and dress in warm clothes. You have a digestive system, which enables you to eat and get nutrients from a variety of foods. You are a well-adapted creature. You have lungs, which allow you to breathe. Yet humans live in such a variety of environments that it is difficult to argue that you are adapted best for a particular land environment. Certainly you have many adaptations for a life on land and are poorly adapted for life in water. You would find it easier to survive in a mild temperate environment that is rich in resources, but your kind survives in every land environment. Humans even successfully venture into seemingly impossible habitats for short periods of time, under the sea and in space. In these habitats we take artificial environments with us; we live within a capsule, submarine or space station. A human, however, is a little peculiar. What allows you to do this? Your most extraordinary adaptation is your brain (see Figure 1.1.1). Your brain is unlike those of other animals because you have few innate behaviours. Your brain is capable of learning throughout your lifetime. This is your greatest adaptation because it allows you to survive in a changing world and in many habitats. But what is an adaptation?

Students learn to:» identify some adaptations of living things to factors in their environment» identify and describe in detail adaptations of a plant and an animal from

the local ecosystem» define the term ‘adaptation’ and discuss problems associated with inferring

characteristics of organisms as adaptations for living in a particular habitat.

ORGANISMS ARE ADAPTED TO THEIR ENVIRONMENT

1.1

5ECOSYSTEMS

Figure 1.1.1 The brain consumes about 20% of your body’s energy but makes up only 2% of your body weight. Is it worth it?

6 BIOLOGY IN CONTEXT: THE SPECTRUM OF LIFE

cockroaches (see Figure 1.1.4). Bacteria dwell on your skin despite your frequent washing and dust mites live off the dust in your home, which is mainly made up of human skin cells that you and your family have lost (see Figure 1.1.3). Even birds and mammals may use your house as a substitute tree.

It is easy to identify some adaptations. The hair on our head keeps our head warm. It is an adaptation. When we are cold, our hands turn blue as our blood vessels leading to our extremities such as our feet, nose and hands contract to reduce the flow of blood to these areas. This reduces heat loss and it is an adaptation. When we are hot, we may sit in the shade to cool down; this is also an adaptation. Adaptations are characteristics of organisms that help the species to survive.

Organisms possess a variety of adaptations that take advantage of beneficial aspects of living in particular environments as well as adaptations to cope with the difficulties. Adaptations are often classified as structural, physiological or behavioural. The terms are largely self-explanatory. If the adaptation is a physical feature, it is a structural adaptation. Ears, the streamlined shape of a sperm cell, and the flattened body of a cockroach are structural adaptations. Physiological adaptations include processes such as the kangaroo’s digestive processes, which allow it to gain nutrients from tough dry grasses, and shivering to keep ourselves warm. Behavioural adaptations are simply behaviours such as putting on a jumper, a snail coming out to feed when it is wet, or the nocturnal activity of a possum. Often a behaviour, a structure and physiology all combine to provide a survival strategy. A spider spins a web (behavioural), has spinnerets from which the web is secreted (a structure), and produces the silk within specialised tissues as a result of a sequence of chemical reactions (physiology). As you read through this unit, try to identify each adaptation as physiological, behavioural or structural.

ADAPTATIONS OF ORGANISMS IN YOUR ENVIRONMENTWatching wildlife programs or reading books about exotic animals and plants could make you think that animals with interesting adaptations can only be found in outback Australia, Africa or the jungles of South America. However, you share your environment with many organisms with fascinating adaptations.

Sometimes the environment has changed a great deal from that to which the animals and plants were originally adapted. Sudden changes can be caused by catastrophic events such as earthquakes, volcanic eruptions and meteors. Humans can also change environments enormously and quickly. Yet, your house is inhabited by many organisms. Your bed is probably the home of bed mites (see Figure 1.1.2). Your kitchen is visited by

Figure 1.1.2 A bed bug. Sleep well!

Figure 1.1.3 A dust mite. Identify some adaptations from the photograph

Figure 1.1.4 A wingless Australian cockroach. Identify an adaptation that it does not share with the cockroaches that invade our houses

7ECOSYSTEMS

as they move through different parts of the environment. Many spiders, such as the orb spinner spider, spin a web and mainly catch and feed on flying insects. Others such as the huntsman spider lie in wait, flattened against the bark of trees. They use their excellent eyesight to spot prey and their well-muscled limbs allow them to pounce on their prey. Their prey includes the many insects that crawl over the tree’s bark. Other spiders have still more elaborate adaptations to capture their prey. The net-casting spider is another common spider. It weaves a web but, unlike the orb spinner, it holds this web as a net between its four front limbs. Hanging from a thread, it waits for insects to crawl below and hurls its net onto them to trap them. Like the huntsman, it requires, and has, excellent eyesight, which allows it to cast its net with accuracy.

A less common spider is the ‘magnificent’ spider. The magnificent spider is one of the two Australian spiders that use a chemical-baited sex trap to capture its prey—male moths. Female moths produce a scent to attract males. The male moths can detect tiny amounts of this scent and they fly towards it in order to mate. The magnificent spider also produces droplets of the chemical with this same scent. To catch a moth, the spider dangles a droplet of scent on a silk thread. When a male moth approaches, the spider twirls the thread in a circular motion. The moth flies towards the sex scent with amorous intent and is trapped in the moving thread.

All of the spiders described above are well adapted to their environments. They have many adaptations in common. They are all well camouflaged and have similar body structure. They have eight jointed legs, which allow them to move quickly and nimbly. They also have jaws to grasp their prey and a poisonous bite. They all digest their prey by secreting a digestive fluid over it. Their prey is digested outside the body and the spider then sucks it dry to obtain its food. Spiders, like most animals, have a range of adaptations, some peculiar to their environment. Others enable survival across a range of habitats. These spiders may all inhabit the same environment but each inhabits a different part of it. They use different feeding strategies to catch different prey in different ways. The special part of an environment occupied by a species is called its niche.

Varied adaptationsMany species of plants and animals have adaptations in which they mimic features of other organisms. Some plants attract flies, as pollinators, by smelling like rotting flesh. Needless to say such foul smelling plants are not

Animal adaptation: spidersIn order to analyse the adaptations of organisms in environments, we will consider one group of organisms common in environments inhabited by humans—spiders (see Figure 1.1.5). You may have spiders that weave their webs on your window ledges and ceilings. You may have had a huntsman spider invade your bedroom. Many of the spiders around your home feed on insects. Part of a spider’s environment includes its food source. Different spiders are adapted to capture different insects, or insects

Figure 1.1.5 Magnificent spider using pheromones to attract and catch moths


often favoured by home gardeners. These types of chemical mimicry are less common than visual forms of mimicry. The Australian ichnumen orchid, for example, is shaped like a large female wasp, and males try to mate with the flower. In attempting to mate, they spread pollen from one flower to another. You have probably noticed large spots on the wings of some butterflies, which mimic the eyes of a larger organism. It is thought that these may be an adaptation to frighten their predator. While such a display may work for some species, others are adapted to be difficult to see. Some insects are shaped so like a leaf or twig that they are almost impossible to see (see Figure 1.1.6).

Plant adaptation: old man banksiaMany animals are part of our environment. We also share our environment with many plants. If you live in an area with well-maintained gardens, you may find it difficult to determine how each plant’s characteristics are adaptations to their environment. One way to study adaptations of these organisms is to find out about their natural habitats. If you have access to natural bushland, you will find it easier to identify plant adaptations and determine how these enable the plants to survive. Many Australian plants can be found in suburban gardens, city parks, the countryside, reserves and national parks.

The adaptations of one plant will be considered here as an example. If you saw an old man banksia growing in a suburban garden, you might wonder at its flower and bark. Some of these features seem to provide no adaptive advantage and the production of the huge flower and thick bark would be expensive in the consumption of energy and materials. However, the huge flower, in any habitat, seems

easy to explain as a reproductive adaptation. The flower produces large amounts of nectar. The flower advertises the nectar to birds, insects and some small mammals that come to feed. As they feed, they inadvertently collect pollen, transferring it to other banksias on which they feed. Thus, the flower is a reproductive adaptation.

In its habitat of poor sandy soil, the banksia’s thick corky bark protects it so that buds beneath the bark spring to life and allow the banksia to grow back after a bushfire, even though its leaves and many of its branches have been burnt. The woody fruit of the banksia also protect the seeds from fire, and after fire they open up to release the seeds. The seeds fall to the ground and germinate in the ash-enriched soil to produce a new generation of banksias. The banksia roots consist of a dense network of fine roots (proteoid roots), which are capable of obtaining nutrients from the very poor soils it inhabits. Thus, the old man banksia (Banksia serrata, see Figure 1.1.7) is well adapted to its environment, which includes fire and poor soil. However, if you had seen this banksia as it struggled to survive in an over-watered suburban garden with rich soil, you might have incorrectly concluded that it was a poorly adapted species. We humans sometimes have peculiar ideas about what is an ideal environment. We sometimes think that for plants, an ideal environment is plenty of water, rich soils and ample sunlight. Yet, an ideal environment is usually the environment to which an organism is adapted even when this environment might seem harsh to us.

Figure 1.1.6 What is this insect’s most striking adaptation?

Figure 1.1.7 Banksia serrata. The banksia was named after Joseph Banks, who arrived in Australia with Captain James Cook. It was also famous as an evil character in children’s stories

9ECOSYSTEMS

DEFINING ADAPTATIONOrganisms live in and are part of an environment. Adaptations can be defined as characteristics that make an organism suited to its environment. This view of adaptation is useful to a biologist questioning whether a certain characteristic helps an organism to survive. The biologist needs to study the organism’s environment to see how the adaptation is suited to this environment. Sometimes there is a clear match between the characteristic and the environment. The stick insect is well camouflaged so that it can lie hidden among the dead twigs of trees it inhabits. The centipede’s flat body shape and many legs allow it to push through the soil and leaf litter as it hunts small prey. However, it is not always easy to infer that a characteristic has evolved as an adaptation to a particular habitat. Organisms are products of evolution. This means that a present-day organism’s characteristics are the products of millions of years of change. During these millions of years, the ancestors of present-day organisms survived in different habitats to which they were adapted. Hence, the characteristics of organisms are not all adaptations to their current environments but may have been inherited from ancestors. This is most obvious among organisms that have drastically changed their habitats over their evolutionary history. Dolphins and whales, for example, are thought to have evolved from land-dwelling mammals that gradually became adapted to aquatic existence. Whales and dolphins are very successful animals. They are well adapted to life in water. Their fins and flukes combine with their streamlined shape to propel

them at great speeds through the viscous medium they inhabit. Their lungs, though, seem an odd adaptation. Lungs are characteristics of air-breathing land vertebrates. It is likely that the lungs of whales and dolphins do not indicate a particular adaptation for their aquatic environment. Rather, they have lungs because they have evolved from land-dwelling air-breathing ancestors and lungs were an adaptation to their ancestors’ environment. Therefore, in studying organisms, we need to be careful not to assume that all characteristics are adaptations to the organisms’ present environment. Some characteristics may be ‘leftover’ adaptations to environments inhabited by ancestors. Other characteristics may have no adaptive advantage at all but may be features that provide no significant advantage or disadvantage.

THE ENVIRONMENTIn this unit, you have seen how organisms are adapted to their environment. The organism’s environment includes both the living things with which it shares its environment, such as the predators and prey, and its non-living surroundings, such as the quality of the soil and the frequency of bushfires. The environment is a product of the interactions between the many organisms and the non-living aspects of the environment that exist together. In the next unit, we begin the study of these relationships so that environments and the organisms that inhabit them can be better understood. In Chapters 2, 4 and 5, more adaptations of a variety of Australian organisms to their environment are discussed in detail.

SUMMARY 1.1» Adaptations are inherited characteristics of organisms

that increase the chance of survival of the species.» Adaptations are also often described as characteristics of

organisms that are suited to the organisms’ habitats.» It is sometimes difficult to infer that the characteristic

of an organism is an adaptation to its particular habitat because:

– the organism may be observed outside the habitat in which it evolved, for example, in a suburban garden

– the characteristic may provide no particular advantage in a particular habitat but has been inherited from

ancestral organisms that inhabited different habitats – it may simply be difficult to be certain how a

particular characteristic helps a species to survive.» Organisms have a range of adaptations to their

habitats. Plants and animals in your environment have a range of adaptations. Many are well adapted to life in a house and its surroundings.

» Closely related organisms, such as spiders, share some adaptations such as body structure, limbs for locomotion and external digestion, but they have specialised adaptations that suit them to their particular habitat, such as the strategies they use to capture prey.


QUESTIONS 1.11 What is an adaptation?2 Give an example of an adaptation you possess. Explain

why this is an adaptation.3 Name one organism that can be found in your home.

Identify one of its adaptations.4 Describe three adaptations of animals from this unit.

Identify each as structural, behavioural or physiological.5 Describe three adaptations of plants from this unit. How

does each increase the chance of survival?6 Figure 1.1.8 shows a cup-moth caterpillar. Cup-moth

caterpillars live on eucalypts. When disturbed, the cup-moth caterpillar sends out bunches of poisonous spikes, which give a severe sting. From the information provided, list two adaptations of the cup-moth caterpillar. Why is it advantageous for the cup-moth caterpillar to be brightly coloured?

7 Why is it difficult to infer that some characteristics of organisms are adaptations to living in a particular habitat?

8 (a) A puffball fungus releases thousands of spores simultaneously. What would be the adaptive advantages of this reproductive strategy? What is one disadvantage of this strategy?

(b) Figure 1.1.9 shows a human fetus inside the womb. What is one advantage of this type of reproductive strategy? What are two disadvantages?

9 The cicada (see Figure 1.1.10) is a commonly seen organism in Australia during summer. Biologists think it lives underground for about 5–7 years before coming

out of the ground to change form and mate. During summer, males produce a spectacular drumming noise. Two students thought that the drumming was an adaptation. Look carefully at the cicada shown and use your knowledge from observations of cicadas to answer the following.

(a) One student inferred that the drumming noise was used to scare away birds and other predators. Another student thought it might be to attract other cicadas.

(i) Why do you think cicadas drum? Explain your reasoning.

(ii) How would you test these different ideas? (b) Most cicadas come out of their holes at night

when they change from their underground form to their flying, tree-dwelling form. Why do you think they do this at night?

(c) One type of cicada, commonly called a double drummer, comes out in the day-time but usually in great numbers at the same time. How might this be an adaptation?

(d) A cicada has a thin pointed tube, going from the mouth region along the centre at the front of the body, which is visible outside the body. Cicadas feed on trees and when underground on tree roots. Why might this tube be a feeding adaptation?

(e) Suggest three other adaptations cicadas have.10 Is school an adaptation? If it is an adaptation,

would you classify it as structural, behavioural or physiological?

Figure 1.1.8 A cup-moth caterpillar Figure 1.1.9 A human fetus inside the womb Figure 1.1.10 A cicada emerging from its shell

11ECOSYSTEMS

YOUR ENVIRONMENT AND ECOLOGYTake a look at your environment. Your environment includes rocks and soil, the air you breathe and water you drink, as well as the buildings in which you live. And you are not alone. You share your environment with a variety of plants and animals. Some are too small to see, such as the bacteria on your skin and the viruses that give you a cold. Others, such as trees, can be huge. These plants, animals and other parts of your environment do not just exist together. They interact with each other.

Plants provide food and oxygen for animals. Animals provide carbon dioxide for plants. Trees provide shelter and nesting sites. Animals pollinate flowers and disperse seeds. Plants and animals need the sun’s light and warmth. Soil is held in place by roots and enriched by leaf litter and animal droppings.

Ecology is the study of such interrelationships between organisms and the interrelationships between organisms and their non-living (physical) surroundings. Therefore, ecology can be simply defined as the study of how organisms interact with other organisms and their physical surroundings.

Consider one local environment inhabited by a school student. A description of the school environment might include details about buildings and classroom interiors, climate and topography, gymnasium facilities and the size of the asphalt playgrounds, the types and numbers of students and teachers, the availability of shade trees and lawns, the pigeons that feast on leftovers between recess and lunch, and the availability of ‘junk food’ at the tuckshop. In short, a complete inventory of the environment would include both the abiotic (non-living things) and biotic (living things).

An ecologist would not be satisfied with such a description as an ecological study of the environment because the fundamental purpose of ecology is to understand the way in which these things interact. For example, what influence does the climate have on the growth of the shade trees? How do these trees affect the distribution of students during lunch? What influence do school holidays have on the availability of food scraps for pigeons and how do the pigeons respond to fluctuating food supplies? In other words, an ecologist is not merely interested in a description of the environment but wants to observe and explain, first, the way in which organisms affect and are affected by other organisms and, second, the way in which organisms affect and are affected by their non-living surroundings.

ECOSYSTEMS AND COMMUNITIESThe basic unit of study in ecology is an ecosystem. The set of interacting organisms in an area together with their non-living surroundings makes up an ecosystem. It can be defined as a self-sustaining group of organisms interacting with its environment. Ecosystems may vary enormously in

Students learn to:» identify the factors that determine the distribution and abundance

of a species in each environment.

Ecosystems: environments, ecology and communities

1.2


size and complexity. An ecosystem could be an ocean or a coral reef, a creek or an aquarium, a forest or a rotting log, the Earth itself or a Petri dish culture of microbes.

Ecosystems may vary in size, but they all have a boundary within which the processes occurring can be studied and across which the energy and material inputs and outputs can be examined. The boundary is usually set for the convenience of the study. In this way, within an area of bushland one ecologist might study a forest ecosystem, another, the neighbouring woodland ecosystem, a third, the nearby heath ecosystem, and still another may choose to study the whole area as a single ecosystem (see Figure 1.2.1). Each has clear boundaries set for the purpose of the study.

An ecosystem can be thought of as being made up of two interrelated parts—the biotic and abiotic components. The set of interacting organisms within an ecosystem is called a community. In ecology, the term ‘community’ does not usually refer to a single species but refers to all the many different interacting plants and animals in the area.

When studying a specific ecosystem, it is convenient to name it. Hence, the ecosystem that is composed of the blue gum forest community and its abiotic environment can be called the blue gum forest ecosystem.

Naming ecosystems and communities is useful because it allows a biologist to communicate something about an environment simply with a name.

Figure 1.2.1 Profile of a bushland ecosystem

SUMMARY 1.2» Ecology is the study of how organisms interact with

other organisms and their physical surroundings.» The non-living aspects of the environment are called the

physical or abiotic components.» The organisms or living things in the environment are

the biological or biotic components of the environment.» An ecosystem is the basic unit of study in ecology.» An ecosystem is a self-sustaining group of organisms

interacting with its environment.

» An ecosystem consists of the biotic (living) and abiotic (non-living) components of an area.

» Ecosystems vary in size and complexity.» The interacting organisms within an ecosystem

are called a community.» Communities are made up of different plants

and animals.» A specific community or ecosystem is often

named by stating its dominant species and its vegetation structure (e.g. blue gum forest community and blue gum forest ecosystem).

Key:

tall red gums

stunted grey gums

grass

13ECOSYSTEMS

QUESTIONS 1.21 Name two plants and two animals, other than humans,

that are part of your environment.2 On a map that shows your school or home, identify at

least two ecosystems.3 Use a common name to identify an ecosystem near

where you live or near your school that you could study.4 What is each of the following? (a) ecology (b) ecosystem (c) community5 What are the two components that make up an ecosystem?6 What two groups of components make up an organism’s

environment?7 Give one example from this unit and one example from

your own experience for: (a) an interaction between organisms (b) an interaction between organisms and their

physical surroundings.

8 What is the basic unit of study in ecology?9 Is mainland Australia one ecosystem or many? Explain.10 What two features of a community or ecosystem are

often included in their name?11 (a) Copy Figure 1.2.2 into your book. (b) Draw lines to indicate the boundaries of three

ecosystems. Suggest possible names for each.

Figure 1.2.2 An aerial view of three ecosystems

In Units 1.3 and 1.4, you will learn how abiotic factors influence the distribution of plants and animals.When you study an organism in an ecosystem, there are two questions that often spring to mind:

how many of them are there, and where are they? The region where an organism is found is its distribution. The number of individuals in an ecosystem is its abundance.

DISTRIBUTIONThe distribution of an organism usually shows the locations in which it can be found. Distributions on a large scale, such as the distribution of an organism in Australia, can be determined by such methods as trapping, personal sightings, and the observation of tracks or traces. The data are collected and the distribution is then often shown on a map (see Figure 1.3.1).

Students learn to:» examine trends in population estimates for some plant and animal

species within a local ecosystem.

The distribution and abundance of organisms

1.3


Figure 1.3.1 Satin bowerbird and its distribution in Australia

When studying a smaller ecosystem, the distribution of a particular organism is sometimes described on maps of the area (see Figure 1.3.2). The method used to determine the distribution usually depends on the nature of the ecosystem itself, the characteristics of the organism under study, and the resources available to the researcher. The methods used to study the distribution of feral cats in a city like Sydney, for example, might differ considerably from the method used to study the distribution of banksias in a coastal reserve.

TransectsThe distribution of plants can generally be determined by identifying individual plants and describing their location in an area. This is usually done by marking out a straight line across an area, noting the types of plants present, and plotting their position along this line on a diagram. This

indicates the distribution of plants along a cross-section of the ecosystem. This cross-section is called a transect (see Figures 1.2.1 and 1.3.3). Although plants are most often the subject of transect studies, the distribution of animals that tend to stay in the same place, such as those on a rock platform, can also be examined with the aid of transects.

On a transect, it is common practice to sketch the topography of the cross-section as a single line and sketch the plants as they occur along the line to show their distribution. Typically, a vertical scale indicates the height of the plants and the distance across the area is indicated along a horizontal scale. Sometimes important factors that may influence the distribution, such as changes in soil type or depth, can also be indicated on the transect (see Figure 1.3.3).

If a different perspective is desired, a series of transects

residential

eucalypts

privet

lantana

Key:tea tree

grass

1 km

residential

oval

industry

creek

Heig

ht (m

)

Distance (m)

80

60

40

20

050 100 150 200 250 300 350 400 450

grasses

lantana

privet

eucalypts

tea tree

Key:

Figure 1.3.2 Vegetation distribution in a suburban reserve

Figure 1.3.3 Transect through in a suburban reserve

15ECOSYSTEMS

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across an ecosystem can be combined to produce an aerial view or surface map of the vegetation distribution. Figure 1.3.3 could have been produced this way.

INVESTIGATION 2 Using a transect to study the distribution of plants

ESTIMATING ABUNDANCEThe abundance of an organism is the number of individuals belonging to the same species in an area. This can most accurately be determined by simply counting every individual in an area. The abundance of people in Australia is determined by counting every person in a census. However, it is often impossible to locate every individual in an ecosystem, and even when it is possible, it is usually too time-consuming and costly. Imagine the time it would take to identify and count each ant in an ant nest, let alone a forest ecosystem.

QuadratsThe abundance of a species in an ecosystem is usually found by taking small samples of the community and using the data obtained from them to estimate the population in the ecosystem as a whole. As with distribution, it is generally easier to find the abundance of a plant than of an animal. The abundance of a plant species is usually determined by marking out a number of small, randomly selected square areas in the ecosystem. These squares are called quadrats. The individuals within the quadrats are counted. The average number per area (density) is calculated and this can be used to estimate the abundance in the whole ecosystem (see Figure 1.3.4).

The size of the quadrats used depends on the characteristics of the organism being studied. A large organism requires a larger quadrat than a small organism. An organism whose distribution is even and consistent requires fewer quadrats than one whose distribution is

Key:

heathland

quadrats

density = 13 Christmas bells per 500 m2,

i.e. m2

abundance = density x total area= x 5000= 130 Christmas bells

Christmas bells

10 m

10 m

2.6100

2.6100

Figure 1.3.4 Quadrats used to estimate the abundance of Christmas bells in a heath

scattered and erratic. A few small quadrats would suffice to estimate the population of grass on an oval whereas many large quadrats would be required to estimate the abundance of the sparsely scattered cedars in an Australian rainforest.

When estimating abundance, a number of quadrats are always selected at random so that any chance variations within the quadrats will even out. This can be explained if we compare the sampling procedures with tossing a coin. To estimate the number of times a tossed coin will land ‘heads’, if tossed a million times, you could take a very small sample, of only two tosses. If tossed twice, a coin might land ‘heads’ twice. This particular sample would result in an estimate of a million ‘heads’ in a million tosses. If a sample of 100 tosses were used, a result closer to 50/50 would probably be obtained. The estimate from this larger sample is likely to be more representative of the actual outcome. The greater the number of quadrats sampled, the better the abundance estimate is likely to be.

The abundance of animals can also sometimes be estimated by using quadrats. The abundance of animals that remain in one place, such as barnacles, sea-squirts or oysters, can be estimated by using quadrats. So too can the abundance of large animals in herds on open plains, and animals that can be easily flushed from definable areas of undergrowth. Quadrats have been successfully used to estimate the abundance of zebras, kangaroos, tigers and ground parrots, for example. Often, however, the fact that animals move makes the use of quadrats difficult.

INVESTIGATION 3 Using quadrats to measure the abundance of plants in an ecosystem

The capture–marking–recapture techniqueA less widely used method of estimating abundance is the capture–marking–recapture technique. In this procedure,

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Figure 1.3.5 An Australian bush rat (Rattus lutreolus), which is not to be confused with the introduced pest, black rat (Rattus rattus) which arrived with the First Fleet

Table 1.3.1 Capture–marking–recapture data on bush rats

CAPTURE (n1) RECAPTURE (n2)

Number caught 15 10

Number marked – 5 (m2)

Abundance = Number captured × Number recaptured Number marked in recapture

i.e. A = n1 × n2

m2

A = 15 × 10 5

A = 30

SUMMARY 1.3» The distribution of an organism is the region that it

inhabits.» The distribution of an organism on a large scale is

usually described by plotting on a map the places in which it is found.

» Transects are often used to determine the distribution of plants.

» A diagram of a transect is often used to show the distribution of plants.

» The distribution of animals can often be determined by personal sightings, trapping or the observation of

tracks and droppings.» The population of an organism is the group of

individuals of the same species in an area.» The abundance of an organism is the number of

individuals of the species in an area.» The abundance of plants and some animals can be

estimated by counting the number of individuals in randomly selected quadrats.

» The abundance of animals can sometimes be estimated by the capture–marking–recapture technique.

» It is usually easier to determine the distribution and abundance of plants than of animals because animals move and may hide.

traps are set in the study area. The animals are captured, marked and released. Traps are reset in exactly the same way and under the same conditions a second time. By comparing the number of marked individuals with the number captured, the population of the animals in the area can be estimated (see Table 1.3.1 and Figure 1.3.5).

The capture–marking–recapture procedure is based on the assumption that the number of marked individuals in the second catch is proportional to the number of marked individuals in the whole population. Using this procedure, let us say that traps were set and 15 individuals were captured, marked and released. Then traps were reset and 10 individuals were captured. If 5 of these 10 were marked, it is reasonable to assume that half of the total population is marked. Altogether, 15 individuals were marked, therefore the total population in the area is 30; that is, twice the number originally marked. More accurate estimates can be obtained by repeating the exercise a number of times and calculating an average.

The capture–marking–recapture sounds good in principle but has problems when put into practice. The technique is based on the assumption that all the marked animals have dispersed evenly among the total population after release. It is also based on the assumption that animals are no more or less likely to be captured in the first trapping than in the second or subsequent trappings. This assumption often does not hold true. Some small rodents, for example, seem to enjoy the food they get when first trapped and seem only too willing to be recaptured. Other animals may be badly frightened by the experience and avoid the traps in future. This problem results in the capture–marking–recapture technique sometimes producing unreliable data.

17ECOSYSTEMS

» Estimates are usually used to determine the abundance and distribution of organisms because it is too difficult or too expensive to find every organism in an environment.

QUESTIONS 1.31 Distinguish between the terms ‘population’ and

‘distribution’.2 Describe how you could determine the distribution of

plants in an ecosystem.3 How could you estimate the number of weeds in a local

area, for example your garden or backyard, a local park or pasture?

4 How could you estimate the population of an animal in your local area, for example the population of cockroaches in your kitchen, snails in your garden, dogs in your street or barnacles on a rock platform?

5 Describe how the information in Figure 1.3.6 on the distribution of koalas might have been determined.

6 Describe how you would estimate the abundance of tea trees on a coastal sand dune.

7 What factors would influence the size and number of quadrats that would be used to estimate the

abundance of an organism?8 Describe in detail how the abundance of wombats in

an ecosystem could be estimated.9 Figure 1.3.7 shows the distribution of saltbush shrubs

in an arid ecosystem. Using quadrats, answer the following questions.

Figure 1.3.6 Koala distribution in Australia

(a) Estimate the saltbush abundance. (b) What is the saltbush density per 100 square metres? (c) Feral camels and donkeys are thought to be

damaging the ecosystem by destabilising sand dunes and feeding on saltbush. Suggest one way in which the extent of their impact could be measured.

10 A group of biology students, with the help of a park warden, obtained the data in Table 1.3.2 when using the capture–marking–recapture technique to estimate the abundance of Antechinus stuartii in a woodland on the New South Wales south coast.

(a) Estimate the Antechinus abundance in the woodland.

(b) How could the accuracy of the estimate be improved?

(c) Why might an ecologist be reluctant to use the capture–marking–recapture technique?

Figure 1.3.7 Distribution of saltbush in an arid ecosystem

Table 1.3.2 Capture–marking–recapture data for Antechinus stuartii in a woodland ecosystem

DAY CAPTURE NUMBER MARKED

RELEASED

1 (capture) 8 8 8

2 (recapture) 6 3 6


Students learn to:» identify factors determining the distribution and abundance of

species in environments.

Factors determining distribution and abundance

1.4

The abundance and distribution of organisms are influenced by a complex range of physical and biological factors interacting in the environment. The particular combination of influences that determine the abundance and distribution of particular organisms is usually unique. However, four major interrelationships can be identified. These are the organism’s interaction with or influence by: » abiotic environmental factors» availability of resources» other members of the same species» other organisms of different species.

ABIOTIC FACTORSOne of the most important aspects of the abiotic environment for terrestrial organisms is climate. Typically, the climate and soil characteristics of an ecosystem interact to determine the types of plants that grow in a region. Since plants generally provide food and shelter for animals, the vegetation in the ecosystem in turn determines the distribution and abundance of animals. Although all of these (animals, plants, soil and climate) interact to maintain the ecosystem, it is ultimately the physical environment that has the most profound influence on the long-term distribution and abundance of organisms.

Figure 1.4.1 The rainbow lorikeet's natural habitat includes forest and woodland. It thrives in well-treed suburbs where people have created an environment rich in food.

19ECOSYSTEMS

While the roles of climate and soil in determining the character of an ecosystem and community are of critical importance, it must be remembered that they are not single factors but represent sets of interacting physical factors. Climate includes such things as the amount and pattern of rainfall, average temperature and temperature range, humidity, and all the regular and irregular atmospheric phenomena that constitute the weather. Soil characteristics include the texture, depth, drainage, quantity and dispersal of humus (decaying material), moisture content and water-holding ability, and the availability of salts such as nitrates, phosphates and sulfates. And these are just some of the non-living factors that combine to provide the fundamental characteristics of the environment to which organisms are adapted.

Within a particular ecosystem, the measurement of these physical factors in the area can often provide evidence to explain and predict the characteristic patterns of distribution. Table 1.4.1 lists some of the abiotic factors that could be examined when studying an ecosystem and briefly states how they can be measured. Further details are given in Investigation 1.

RESOURCESAnything an organism uses is a resource. Plants have a fundamental role in the community as a resource for animals. Resource needs of animals include such things as food, living space, shelter, nesting sites, nesting materials, oxygen and water. The availability of these can play a critical role in the abundance and distribution of organisms.

Sometimes the availability of a single resource may be the single factor that determines the maximum population of a particular species in an area. Such a factor is called a limiting factor. For example, many Australian birds, bats, possums and gliders nest in the hollow branches of eucalypts. These hollows typically begin to occur in the dead branches of trees that are about 100 years old; see Figure 1.4.2. Large hollows suitable for the possums and parrots may not develop until trees are 150–200 years old.

Figure 1.4.2 A possum nested in tree hollow. What might be the abundance if old trees are cut down?

Table 1.4.1 Abiotic environmental factors and their measurement

ABIOTIC FACTOR MEASUREMENT*

Light intensity Light meter

Air temperature Thermometer

Daily temperature range Max./min. thermometer

Relative humidity Wet and dry bulb thermometer

Rainfall Rain gauge

Wind Anemometer

Soil temperature Soil thermometer

Soil depth Digging to expose soil profile and measuring

Soil moisture Comparison of wet and dry weights

Soil porosity Rate of water flow through sample

Humus Estimating leaf litter depth and comparing burnt and unburnt soil weights

pH Indicator and pH chart

Soil mineral nutrient Soil test kit

* For more detail on measurement techniques see Investigation 1.

INVESTIGATION 1 Measuring physical characteristics of an ecosystem, and observing incidence of human impact

If these large old trees are logged from forests, the population of many birds and mammals can decrease rapidly in a single breeding season. Even if similar eucalypt species are replanted to produce a young robust forest, it may be hundreds of years before suitable hollows

p48


reappear. Nevertheless, the populations can to some extent be preserved if artificial nesting boxes are provided and reserves containing stands of mature trees are established throughout the forest. Similarly, the provision of nesting boxes in suburban gardens and reserves can help to

maintain and increase the abundance of many parrots and possums.

INVESTIGATION 4 Distribution and abundance of animals

Abun

danc

e

Time

no additionalnesting boxes

additional nesting boxes provided

Figure 1.4.3 The abundance of parrots and the influence of nesting sites

Figure 1.4.4 Eucalyptus fruit and flowers

SUMMARY 1.4» The distribution and abundance of organisms can

be affected by a variety of factors including abiotic environmental factors, availability of resources, other members of the same species, and organisms of different species.

» An examination of variations in these factors within an ecosystem can often provide an explanation for the distribution and abundance of organisms within that ecosystem.

» The distribution and abundance of a particular organism is usually determined by a number of interacting factors.

» A resource is anything that is used by an organism.» When a single resource, such as breeding sites or food, is

the factor that limits the abundance of an organism, it is called a limiting factor.

QUESTIONS 1.41 List the four main interrelationships that influence the

distribution and abundance of organisms.2 List some of the main abiotic factors that may influence

the distribution and abundance of an organism.3 Explain why it can be said that the physical

environment ultimately determines the distribution and abundance of organisms.

4 (a) Describe the distribution of one plant and animal in your local area.

(b) For both the plant and animal answer the following questions.

(i) Why do you think it is found in the areas shown?

(ii) Is it more common in some places than others? Explain.

5 Carnivorous plants, which capture and digest insects, often dominate impoverished, water-logged soils but are rare where soils are rich and well drained.

(a) What factors influence their distribution? (b) Why can they survive in soils where few

other plants can?6 In terms of the abundance of organisms, what is meant

by a limiting factor? Is there a single limiting factor controlling the abundance of any organisms in your area?

7 Suggest the main abiotic factors you would examine in a terrestrial ecosystem and state briefly how you could measure them.

8 Suggest some of the main abiotic factors you would examine in an aquatic ecosystem.

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21ECOSYSTEMS

Students learn to:» compare the abiotic factors of aquatic and terrestrial environments.

Comparing the abiotic factors of terrestrial and aquatic environments

1.5

In Unit 1.4, you saw how the abundance and distribution of organisms could be explained in terms of abiotic factors and resources. In this unit, the abiotic factors of aquatic (water) and terrestrial (land) environments are compared to illustrate the different abiotic factors and resources that exist in these two very different environments.

From a human perspective, it is all too easy to regard the aquatic environment as hostile and unforgiving. Yet water provides an environment in which it is much easier for life to exist than land does. It is thought that life first evolved in water, and water is the major component of all living things.

PHYSICAL CHARACTERISTICS

ViscosityViscosity is a measure of how difficult it is to move through a substance. For example, consider the viscosity of water and honey. If you dropped a ball-bearing into a glass of honey and a glass of water, the ball-bearing would fall much more slowly through the honey than through the water. Honey is more viscous than water. If we extend the experiment a little further by dropping the ball-bearing into a glass containing air, then the ball will fall faster through the air than through the water. Water is more viscous than air.

Viscosity is an important feature of the aquatic and terrestrial environments and it is one area in which a terrestrial existence provides an advantage over the aquatic environment. It is much easier for animals to move through air than through water. Many aquatic animals have a streamlined shape, which allows them to move more easily in water.

BuoyancyBuoyancy is a measure of a substance’s ability to support or hold up an object. For example, a cork is easily supported by water, but the same cork will fall through air. Water provides greater buoyancy than air. Air appears to offer no support at all. However, this is not true—air does provide some support. If you drop a sheet of paper, the buoyancy provided by air can be observed, but highly specialised adaptations, such as wings, are required to make any use of it.

In this way, water provides an advantage over the terrestrial environment because it provides greater support for an organism and this support is more than a mere upward thrust. Organisms are surrounded by water, which not only helps to hold them up but, in some cases, also maintains their very shape. A jellyfish, for example, quickly collapses into a deformed blob when removed from water.


Temperature variationThe terrestrial environment can experience huge variations in temperature in very short periods. Within a single day, variations of 15–20°C are not uncommon, and far greater temperature fluctuations can occur in desert environments. Even relatively small bodies of water do not experience such temperature variations. Water temperatures change much more slowly and this can be very frustrating for early summer beach-goers who swelter in high temperatures on land but find the water still too cold for anything more than a quick dip.

Except at the very edges, the temperature of the oceans remains constant from year to year. Indeed, any slight variation in oceanic temperature could have quite disastrous effects. For example, an increase in ocean temperatures of only a few degrees could change global weather patterns, melt Arctic and Antarctic ice, and expand the volume of the ocean enough to flood coastal cities.

Since it is much easier to adapt to a constant environment than to varying conditions, the constant temperatures of the aquatic environment are much more conducive to life than the varied temperatures experienced on land.

Conduction of heatAlthough temperatures remain more constant in water than on land, organisms tend to lose heat more rapidly in water. This is because water conducts heat better than air. People lost at sea probably die more often from heat loss (hypothermia) than by drowning because heat is so quickly lost to the surrounding water. Aquatic birds and mammals whose body temperatures are higher than that of the water they inhabit must be adapted to prevent this heat loss by conduction.

Availability of gasesOrganisms need oxygen for respiration, and plants need carbon dioxide for photosynthesis. As almost 20% of air is oxygen, it is abundant on land except at very high altitudes. Much less carbon dioxide is available since only about 0.03% of air is carbon dioxide, but this appears to adequately provide the needs of photosynthesis in plants.

Oxygen and carbon dioxide dissolve in water. Where water is in close contact with the air, both are readily available. In particular, these gases are most abundant where turbulent water is tossed through the air in places such as river rapids, waterfalls and breaking ocean waves. The dissolved gases are then gradually mixed throughout

the water by slow convection currents. Nevertheless, as water depth increases, the availability of both gases decreases. Stagnant ponds and pools, too, often lack sufficient oxygen for the survival of most organisms.

The availability of gases in water is also affected by temperature. When you heat water, you will notice the small bubbles that form well before the water boils. These are bubbles of air that come out of solution as the water heats up. As temperature increases, the solubility of gases in water decreases. This means that there is less oxygen and carbon dioxide in warm tropical seas than in Arctic and Antarctic oceans. However, the abundance and variety of life in the tropical marine environment shows that enough of both gases is available.

Diffusion of gasesThe movement of gases through water and air can be influenced by wind and currents, but their movement into and out of cells depends on diffusion. The diffusion of gases is about 10 000 times faster through air than through water. As a consequence, air provides a tremendous advantage for the rapid movement of gases. However, to gain entry to cells, gases must dissolve in water to pass through the cell membrane. This is why any surface used for gas exchange must be moist.

Availability of waterOn land, water is at a premium. It is quickly lost from organisms by evaporation and must be replaced constantly. In an aquatic environment, water surrounds organisms and yet it may not be as readily available as you might imagine. In a freshwater environment, water tends to constantly diffuse into organisms. This is because cells contain more ions and organic substances than the surrounding water. This causes a net movement of water into the cells. By contrast, in the marine environment, cells often have a lower concentration of salts than the surrounding water. Under these conditions, there is a net movement of water out of the cell (see Figure 1.5.1). (For more information about this movement of water into and out of cells, see Unit 2.5.)

Availability of ionsOn land, ions (salts) are available in soil water. Plants absorb these through their roots and animals obtain them when they feed off plants or other animals. Some soils lack essential ions and few plants will grow under such conditions. Conversely, some soils, particularly in Western

23ECOSYSTEMS

Australia and Victoria, contain excessive salts and this prevents plant growth because water diffuses from the roots into the soil rather than from the soil into the plant. In the marine environment, most ions are available in abundance. Just as convection currents carry oxygen and

carbon dioxide to the ocean depths, so, too, these same currents return ions from decomposed organisms to the surface. Nevertheless, some ions such as those of calcium are in demand by so many organisms for the production of calcium carbonate shells that its availability may limit the abundance of some animals (see Figure 1.5.2).

LightOn land, light is available in abundance. It is generally only scarce on the floors of dense forests and caves. In water, light is often at a premium. The surface of water reflects light. This means that only about 70% of the light that strikes the surface penetrates. Furthermore, water absorbs light. Therefore, as depth increases, light availability decreases. On the ocean floors, there is no light for photosynthesis or vision and both plants and animals have become adapted to cope with the difficulties this presents (see Figure 1.5.2).

Pressure variationsOn land, there are frequent fluctuations in pressure. Typically, these are measured regularly and included in daily weather reports. However, these variations are small and have little direct impact on organisms. In water, by contrast, although pressures do not fluctuate, there is considerable variation. As water depth increases, pressure increases (see Figure 1.5.2). Pressures are so

(a) cell wallcell membrane

water in

water out

Water diffuses in and out of the cell across the cell membrane.

More water enters the cell by osmosis than leaves the cell—the concentration of substances is greater inside the cell than outside.

(b)

water in

water out

Water diffuses in and out of the cell across the cell membrane.

More water leaves the cell by osmosis than enters the cell—the concentration of substances is greater outside the cell than inside.

cell wallcell membrane

Figure 1.5.1 Osmosis in (a) fresh water and (b) salt water

Figure 1.5.2 Comparing surface water and deep ocean water in an ocean

light

light reflected

low pressure

no light

high pressureionsfrom deadorganisms

gases dissolve

waters

waters

Surface

Deep

ionsabundant

gases more abundant

light penetrates

light absorbed


great on the floors of the deepest oceans that they can crush submarines. Yet despite the tremendous pressures, specially adapted animals do inhabit the ocean depths.

These organisms were first studied by dragging nets along the ocean floor behind surface ships, but the animals captured were sometimes so distorted when brought to the low pressures on the surface that their original appearance was altered. More recently, specially designed vessels have permitted some exploration of this environment. However, the difficulties faced by such research have prompted some scientists to argue that more is known about outer space than about the ocean depths.

INVESTIGATION 1 Measuring physical characteristics of an ecosystem and observing incidence of human impact

Figure 1.5.3 Rock pool

SUMMARY 1.5» Life probably first evolved in water. Water provides an

environment in which it is easier for life to exist than on land.

» Water is more viscous than air. Therefore, it is more difficult to move through water than through air.

» Water is more buoyant than air. Therefore, water provides greater support for organisms than air.

» Temperatures vary less in water than on land. Ocean temperatures are fairly constant. Constant temperatures are easier to adapt to than varying temperatures.

» Water is a better conductor of heat than air. Therefore, a body immersed in water will rapidly lose heat to its surroundings.

» Gases (e.g. oxygen and carbon dioxide) are available in greater abundance on land than in water.

» The availability of gases decreases with altitude on land and decreases with depth in water.

» Gases diffuse more quickly through air than through water.

» Water can be lost quickly by evaporation from exposed surfaces on land.

» In the freshwater environment, the concentration

gradient favours the movement of water into most cells.

» In the marine environment, most ions (salts) are readily available. In freshwater, ions are in very low concentrations. On land, most ions are readily available in solution in soil water, though some soils contain an excess of salts while others contain too little.

» Light availability in water decreases with depth.» On land, air pressure may fluctuate quickly but it

has little direct effect on organisms.» Air pressure decreases with altitude. Water

pressure increases with depth.

QUESTIONS 1.51 List three advantages and three disadvantages for

life in the terrestrial and aquatic environments that are related to their abiotic characteristics.

2 Why do most fish have a streamlined body shape?

3 Why do land animals need larger muscles and bones for support than aquatic animals?

4 Why is the concentration of oxygen higher near the surface than on the bottom of the oceans?

p48

25ECOSYSTEMS

In Unit 1.5, you compared the abiotic factors of terrestrial and aquatic environments. This comparison revealed the different challenges faced by life on land and life in water. You learnt in Unit 1.1 that an ecologist would be dissatisfied with this comparison. An ecologist would want to know about the relationships between the abiotic factors and the organisms that live in the environment. To consider all the abiotic factors and their varied influences would be too large a task in this book. So, in the next two units the effects of selected aquatic and terrestrial abiotic factors will be analysed. First, the influence of light availability on aquatic and terrestrial environments will be considered in this unit. Then, in Unit 1.7 the distribution of communities across Australia will be explained in terms of a variety of terrestrial abiotic factors including rainfall, temperature and soil quality.

LIGHT IN WATERLight provides the energy requirements of virtually all living things. On land, it is generally abundantly available. In water, useful amounts of light are only available to a depth of about 100 m depending on the water clarity. The lack of light is brought about by two factors: first, about 30% of the light that strikes the water’s surface is reflected; second, water absorbs light.

Water does not absorb all wavelengths of light equally. The different wavelengths of light, which we see as colours, make up the colour spectrum of white light. If you have been snorkelling or skin-diving, you will realise that underwater things take on a green or bluish tinge. This is because the red and orange wavelengths of light are quickly absorbed by water. The degree to which water absorbs the different wavelengths of light is called the absorbance spectrum of water (see Figure 1.6.1).

5 Why is the salt calcium carbonate in high demand in the marine environment?

6 (a) Why do both marine and terrestrial organisms need to be adapted to avoid excessive water loss?

(b) Why don’t freshwater organisms require similar adaptations?

7 Why is it eternally dark on the ocean floor?

8 Why don’t many aquatic organisms require mechanisms to regulate their body temperatures?

9 The terrestrial environment is sometimes described as a two-phase environment, whereas the aquatic habitat is sometimes said to consist of a single phase.

(a) Explain what is meant by this statement. (b) To what extent do you agree?

Students learn to:» identify factors determining the distribution and abundance of organisms

in aquatic environments.

The distribution and abundance of organisms: the influence of light

1.6


Green, red and brown algaeFigure 1.6.1 shows the absorbance of light in water. The graph reveals a major problem for aquatic plants. Water absorbs the very wavelengths of light that are used most by chlorophyll for photosynthesis. This means that as depth increases, not only the quantity but also the quality of light decreases.

Plants have evolved a variety of adaptations to make the best possible use of the light available in water. Red and brown algae contain coloured materials (pigments), which absorb the light that penetrates to the greatest depth in water (see Figure 1.6.2). The red pigment

(phycoerythrin) and the brown pigment (fucoxanthin) absorb the blue and green wavelengths of light. The energy is then transferred to chlorophyll, which carries out photosynthesis. This allows red and brown algae to live at a much greater depth than green algae. If you visit a rock platform at low tide, it is easy to observe a green band of algae exposed on the rock surface, a red band of algae lower on the rock platform, and brown kelp at the greatest depth, usually covered by water even at low tide.

ANIMAL ADAPTATIONSThe lack of light in deep water also presents major difficulties for aquatic animals. We humans rely heavily on sight as our main means of obtaining information about our surroundings, but this is not true of all animals. Dogs, for example, live largely in a world of smells because they rely mainly on their sense of smell. Since sight may be of little consequence to them, the lack of light in the ocean depths poses few problems for the animals that dwell there.

Many aquatic animals rely heavily on smell and sound rather than sight. A few even produce their own light, which is called bioluminescence. This may help them attract a mate or lure unsuspecting smaller animals to a predator’s wide-set jaws. In this blind world, some animals use senses that humans do not possess. Electric eels, for example, are sensitive to the minute electrical impulses given off by the nerves in the muscles of other animals. The platypus’s bill is similarly sensitive and it detects prey, such as yabbies, in the same way. Such adaptations are advantageous both in deep oceans and in shallow, murky freshwater.

Finally, the problems related to lack of light are not limited to aquatic habitats. At night, there is little light in the terrestrial environment. Yet many animals are nocturnal. In Australia the vast majority of mammals are most active at night. Many bats, with the exception of flying foxes, see poorly and yet they are one of the most successful mammals. In short, it is only our peculiar human perspective that makes us see darkness and dim light as a hostile environment. Had this chapter been written by a bat, it may have discussed adaptations to cope with the bright light of day!

In this unit, the adaptations of organisms to one abiotic factor, light, have been considered and the way in which light availability influences the distribution of algae has

10 m

100 m

1 m

visible light

ultraviolet infrared

solar energy reaching ocean surface

only 45% of light energyreaches 1 metre

about 16% reaches10 metres

only 1% remains at100 metres

1000300 400 500 600 700Sea surface

increasing depth

Wavelength(nm)

Figure 1.6.1 Light absorbance by water

Abso

rban

ce

violet blue green yellow orange red

water(5 m deep)

Light

phycoerythrin

fucoxanthin

chlorophyll-a

Figure 1.6.2 Absorption of light by pigments in green (chlorophyll), red (phycoerythrin) and brown (fucoxanthin) algae

27ECOSYSTEMS

been described. Variations in many other abiotic factors also influence the distribution of organisms in aquatic environments. These include:

extremely salty Dead Sea to fresh water with almost no salt

and geysers through warm tropical seas to freezing Antarctic oceans

surface waters to extreme pressure in deep ocean trenches

stagnant ponds to plentiful in the turbulent waters of oceans and cold streams

near hot gas outlets on the ocean floor.These and other factors influence the distribution of various organisms, since different organisms are adapted to different conditions.

SUMMARY 1.6» Light provides the energy needs of virtually all

organisms.» Water reflects and absorbs light. Therefore as depth

increases, the amount of available light decreases.» The colours of light absorbed most by water are

similar to those absorbed most by chlorophyll (see Figure 1.6.1). The wavelengths needed for photosynthesis are quickly absorbed by water.

» Red and brown algae contain red and brown pigments, which absorb the light that penetrates to the greatest depth.

» Red and brown algae are more abundant in deeper water than are green algae.

» Algae are distributed near the water surface and not at great depths in water.

» Life is abundant near hot gas outlets on the ocean floor where chemosynthetic bacteria are the producers.

QUESTIONS 1.61 Why is light generally more abundant on land than

in water?2 Describe the main problems for photosynthesis in

water that are related to light.

3 Why do objects collected under water sometimes have a different colour when they are brought to the surface?

4 (a) Explain why red and brown algae can survive at greater depths of water than green algae.

(b) How does this explain the distribution of red–brown and green algae on a rock platform?

5 Do red and brown algae contain chlorophyll? Explain.

6 What is the advantage for a terrestrial plant in growing tall?

7 Describe how aquatic animals are adapted to environments with no light.

8 Use library resources to investigate how abiotic factors influence the distribution and adaptations of organisms in an aquatic environment. Two of the most interesting ecosystems you could investigate are:

(a) coral reefs, such as the Great Barrier Reef (b) ecosystems found near hot gas outlets and

near mid-ocean ridges on the ocean floor.


Students learn to:» describe the roles of photosynthesis and respiration in the

transformation of energy in ecosystems» identify the general equation for aerobic cellular respiration and

outline this as a summary of a chain of biochemical reactions» identify the uses of energy by organisms» describe the flow of energy through a natural ecosystem» describe the role of decomposers in an ecosystem.

The flow of energy and matter in an ecosystem

1.7

USES OF ENERGY BY ORGANISMSThe energy available to organisms in an ecosystem is used in a variety of ways, including movement, making sound, carrying out chemical reactions as part of cellular metabolism, producing heat and, in some organisms, producing light. You are probably familiar with using energy for sound, movement and heat as you talk, walk and maintain your body temperature, but energy is also used by some organisms to produce light. Glow worms, flash-light fish and fireflies, for example, all use chemical energy to produce light. This process is bioluminescence, which is a spectacularly efficient process because, unlike all human systems devised to provide light, when organisms convert chemical energy into light energy almost no heat is produced. Thus, organisms again demonstrate that biology and evolution have succeeded in developing efficient systems beyond the capacity of human invention. The efficiency of this light-producing system is one reason for their extensive study by biologists. Another is the sheer beauty of the biochemical systems and the extraordinariness of the organisms.

ENERGY TRANSFER AND LOSSIt is a fundamental law of science that energy cannot be created or destroyed. It can, however, be changed from one form to another. In an electric toaster, for example, electrical energy is converted into mainly heat energy. When a match burns, chemical energy is converted into heat and light energy. When you shout, some of the chemical energy in glucose is converted into sound energy. (This actually involves a series of energy changes—you might like to try to draw up a list of them.) However, these energy transfers are not perfect. Whenever energy is changed from one form to another, some energy is lost. In car engines, for example, a lot of the energy we would like to see transformed into moving the car is lost as waste heat and sound.

ENERGY TRANSFER THROUGH ECOSYSTEMSIn ecosystems, the initial source of energy for the community is light. Plants absorb some of the light energy from the sun. Some of this light energy is converted, through photosynthesis in the chloroplasts, into chemical energy in glucose molecules. This glucose can then be transported to other parts of the plant. Typically, about half of it is broken down in respiration to make energy available for cellular processes. The rest of the glucose is converted into larger carbohydrates and other organic compounds (see Figure 1.7.1).

29ECOSYSTEMS

are very different biochemically.When animals (herbivores) eat and digest plants, the

complex carbohydrates are converted back into glucose. This glucose can be broken down by respiration in the animal cells to provide the animal’s energy requirements (see Figure 1.7.2). Similarly, when animals (carnivores) eat other animals, they can make use of the chemical energy stored in the substances of the dead animal’s body.

THE CYCLING OF MATTER IN ECOSYSTEMSIn photosynthesis, the carbon dioxide obtained from air and the water absorbed from the soil are used to produce glucose. From this, other carbohydrates can be manufactured within the plant cells. Some of the carbohydrates are used, together with the nitrates, sulfates and phosphates, which have been absorbed from the soil, to produce proteins and nucleic acids. Other elements obtained from the soil and incorporated into plant tissues include calcium, magnesium, iodine, cobalt, molybdenum, and many others. In this way, matter from the physical surroundings, in the form of simple salts and gases, is absorbed by the plant and converted into complex organic

Figure 1.7.1 Energy transfer from light to plant cells

Figure 1.7.2 Energy transfer from plants to animals

Photosynthesis and respiration are both processes made up of a chain of chemical reactions, which are controlled in cells by many enzymes and factors. Two equations can be used to summarise these complex processes.

Photosynthesis is often summarised as:

carbon dioxide + water glucose + oxygen

This summary shows the reactants in photosynthesis (carbon dioxide and water), the energy source (light) and the products (glucose and oxygen). It does not show the many steps involved in the process. Nor does it show the role of enzymes and other factors.

Respiration is often summarised as:

glucose + oxygen water + carbon dioxide + energy

Again this reaction tells nothing of the many steps or enzymes or factors in the process but it does summarise the equation, showing the reactants and the products, and indicates that energy is made available as a result of the process. In living systems, photosynthesis converts light energy into chemical energy, and respiration serves to make this energy available for cellular functions. Respiration and photosynthesis are not opposite reactions; the steps in the reactions are very different. The reactions

light

photosynthesis glucosetransported

throughout the plant

respiration energy for cell processes

chlorophyll

light energy

converted into other carbohydrates

(starch, sugar etc.)

eaten by animalcarbohydrates

digested to glucose

respirationenergy for

animal processes

plant

converted into other substances


substances, some of which are used to produce the plant’s tissues. When an animal eats a plant, some of the digested material is used to produce the animal’s tissues.

The role of decomposersWhen a plant or animal respires, water and carbon dioxide are returned to the atmosphere. As animals release waste urine or faeces, materials are returned to

their surroundings. When plants and animals die, they are decomposed, returning their remaining nutrients to their physical surroundings. The decomposers, mainly bacteria and fungi, recycle matter. They decompose dead plant and animal material, making nutrients available to plants (see Figure 1.7.3). The result is a transfer of matter from organisms to the physical environment. These materials can then be taken in again by plants to continue the cycle. Unlike energy, matter moves in a cycle through the ecosystem. It is transferred from the physical surroundings to plants, from plants to animals, and from plants and animals back to the physical surroundings.

This matter cycle is actually made up of a number of cycles including, among others, the carbon/oxygen and nitrogen cycles and the water cycle. These cycles are described in Figures 1.7.4–1.7.6.

Although, in time, all the matter is eventually recycled through ecosystems, within a specific ecosystem matter can enter and be lost across ecosystem boundaries. Nevertheless, no ecosystem can sustain a long-term net loss of matter. In time, a balance must be achieved between the gain and loss of matter.

Figure 1.7.3 How matter is cycled through an ecosystem

salts urine faeces

death and decay

water plants animals

carbon dioxide

respiration

Figure 1.7.4 The carbon–oxygen cycle (simplified)

31ECOSYSTEMS

denitrifying bacteriain waterlogged soil

dead animalsand plants

animalwaste

nitrifying bacteriaplant proteinmade with nitratesand absorbed byplant roots

nitrogen gasin the air

Lightningproduces nitrates.

nitrogen-fixingbacteria in rootnodules of acaciaspeas, beans andclover

nitrates inthe soil

nitrogen-fixingbacteria inthe soil

Animals eat plants,synthesising animalprotein.

animalprotein

Figure 1.7.5 The nitrogen cycle (simplified)

Figure 1.7.6 The water cycle (simplified)

precipitation as rain, snow, hail, sleet

water stored as ice and snow

clouds and water vapour

Water evaporates from oceans, land, forests, farms, lakes, rivers, swamps.

ocean

lakes

forest

rivers

underground water

ground run-off


Students learn to:» identify examples of allelopathy, parasitism, mutualism and commensalism

in the ecosystem and the role of organisms in each type of relationship» outline factors that affect numbers in predator and prey populations in the

area studied» describe and explain the short-term and long-term consequences on the

ecosystem of species competing for resources.

Interrelationships among organisms

1.8

SUMMARY 1.7» Light energy from the sun is the original source of

energy for ecosystems.» Plants convert light energy to chemical energy in

glucose through photosynthesis.» Animals obtain energy in the form of chemical energy

in food. This is mainly in the form of carbohydrates.» The chemical energy in glucose is made available to

plant and animal cells through cellular respiration.» Organisms never obtain all the energy available in their

food source because energy is constantly being used and lost by organisms as waste heat; and energy is lost in every energy transfer.

» Energy is lost from plants and animals mainly as waste heat energy. This results in a loss of energy from the ecosystem.

» Energy is not recycled in an ecosystem.» Matter is recycled in an ecosystem.» The recycling of matter in an ecosystem occurs

through a number of interconnected cycles (see Figures 1.7.4–1.7.6).

QUESTIONS 1.71 What is the original source of energy in ecosystems?2 (a) In what form do cells obtain energy for use in

cellular processes? (b) By what process is light energy converted into this? (c) By what process is the energy made available

within cells?

3 What substances in plants are the main source of energy for animals?

4 When an animal eats plants, it never obtains all the energy in the plants it eats. Why?

5 In the physical environment, what substances provide the initial source of material for living things?

6 (a) What substances in plants provide the main sources of materials for animals?

(b) How do plants obtain these substances?7 How do plants and animals release matter to the

physical environment?8 What eventually happens to all the matter in a

community?9 People sometimes remove dead logs from forests for use

in fireplaces, and leaf litter for use as garden mulch. Explain the long-term consequences of these actions in relation to the flow of matter and energy within the ecosystem.

10 When areas of natural vegetation are cleared for agriculture, the land sometimes turns out to be impoverished and inadequate for crops.

(a) Where have all the nutrients gone? (b) How was the original ecosystem maintained?11 A group of people are isolated and have only grain and

chickens as food sources. Should they: A feed the grain to the chickens and eat the

chickens? B feed the grain to the chickens and eat the eggs

the chickens lay? C eat the grain and the chickens? Explain your answer.

33ECOSYSTEMS

INTERRELATIONSHIPS BETWEEN MEMBERS OF DIFFERENT SPECIESWithin a community, two organisms sometimes have no observable effect on each other. However, different species within an ecosystem can often influence one another. Some of the main types of interrelationships are considered in this unit.

MutualismA relationship between two organisms in which both benefit is called mutualism. Examples of mutualism include the alga and fungus that make up a lichen, the alga and polyp that make up coral acacias with their nitrogen-fixing bacteria, and the bacteria in the digestive systems of many herbivores that digest cellulose.

No large animals can digest cellulose. All grazing animals must rely on symbiotic bacteria or protozoa in their digestive systems to break down cellulose. Kangaroos have an additional stomach near the beginning of the digestive tract. This contains the bacteria and protozoa that break down the cellulose in grass. Both the kangaroo and the bacteria benefit from the relationship. The kangaroo obtains access to an additional food source and the bacteria have a habitat with a constant environment and an ample supply of food. All herbivores have symbiotic protozoa and bacteria in the gut, but few can match the efficiency of the kangaroo’s digestion.

CommensalismCommensalism is a relationship between two organisms in which only one benefits and the other is unaffected. Some examples of commensalism include the anemone fish and the sea anemone, and the remora fish and the shark. The anemone fish lives among the tentacles of sea anemones, gaining protection from predators. The anemone appears to receive no benefit. The remora hitches a ride on sharks. It gains a free ride and feeds on scraps from the sharks’ food but appears to provide no service to the sharks.

ParasitismParasitism is a relationship in which one organism lives in or on another organism and feeds from it. The organism in, on or off which a parasite lives is called its host. Well-adapted parasites cause little harm to their host. Their host remains healthy and able to provide them with a habitat and food. Many tapeworms live attached to the lining of the digestive system of their host animal and absorb digested food without causing any serious harm. Some less well-adapted parasites cause discomfort, which irritates

the host and triggers responses aimed at getting rid of the parasite. Ticks and fleas, for example, feed off dogs, who scratch and gnaw at their coats in an attempt to remove them. Some parasites, such as disease-causing bacteria, bring about illness and can kill their host. These disease-causing parasites are called pathogens.

AllelopathyAllelopathy is a relationship in which one organism directly hinders the growth or development of another by releasing toxins. Some plants and fungi produce antibiotics that prevent the growth of bacteria. Sir Alexander Fleming’s discovery that bacteria did not grow around the fungus Penicillium notatum led to the development of the antibiotic penicillin.

Plants may also release substances that inhibit the growth of other plants. Sometimes substances are secreted by the roots. Lantana is an introduced plant that has become a pest in the Australian bush. It not only crowds out native species by competing for soil nutrients and light but also appears to release substances into the soil that inhibit the growth of some native species. Plants may also indirectly inhibit the growth of other plants. The decomposition of pine needles can result in soils that are too acidic for the germination and growth of many plants. Inhibition is not limited to exotic plants. The decay of eucalyptus leaves, for example, can render soils unsuitable for some introduced plants. In each of these cases, the plant’s chance of survival has been increased by reduced competition for resources.

PredationA relationship in which one organism eats another is called a predator–prey relationship, or predation. The term is usually only applied to relationships in which one animal eats another. Dingoes and wallabies, lions and zebras, orb-spinner spiders and beetles are all examples of predator–prey relationships.

Predator–prey relationships often have a major impact on the abundance of organisms. Indeed, prey and predator populations are sometimes so closely related that graphs of their abundance may look very similar. Figure 1.8.1 shows the effects of a predator–prey relationship between two mites that were studied under laboratory conditions.

The shape of the graphs can be explained in the following way. The predator mite eats the mite of a different species, which is its prey. When the prey population increases, there is more food for the predator and therefore the predator population increases. As the


with the limpet (Cellana) (see Figure 1.8.2). Both feed on the algae growing on the rocks. The periwinkle moves faster, but feeds less efficiently than the limpet. If the periwinkles are removed, the limpet population increases. Where there are many periwinkles, there are few limpets. Nevertheless, some algae are always left behind by the periwinkles and this ensures the continued survival of the limpets.

Consequences of competitionWhen two species compete for the same resources, one of the species usually loses. In the short term, this results in a decrease in the abundance of one of the species. The effects of competition on the population of organisms

Figure 1.8.2 Black periwinkle (Nerita) (top) and limpet (Cellana) (bottom) compete for food

predator population increases, more prey is consumed. The predator population falls again because there is less food, and the cycle begins once more. This causes the populations of both organisms to fluctuate in the same pattern. Both the predator and the prey graphs have a similar shape, but the predator population change always lags behind that of the prey and the predator population is usually less than the prey population.

Such obvious relationships are seldom observed under natural conditions because many variables interact to influence the abundance of both predators and prey. In particular, where predators have a variety of food sources, such simple patterns are not observed.

CompetitionCompetition is a relationship in which two organisms compete for a limited resource. Competition between organisms in the same place for the same set of resources usually results in the elimination of the less successful one. The introduction of dingoes and, more recently, feral cats and foxes has been blamed for the reduced population of some native carnivores in parts of Australia.

Sometimes organisms are fairly evenly matched in their competition for resources. Such organisms may coexist indefinitely. In rainforest, for example, the availability of light is often at a premium for seedlings. Therefore, there is constant competition for light. Nevertheless, no single species dominates and the rainforest remains an exceptionally diverse community. Competition is most intense within a single species population because all the individuals require the same resources.

Occasionally one species is more successful than another and yet both continue to coexist. On the rock platform, the black periwinkle (Nerita) competes for food

prey

predator

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1000

800

600

400

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20

15

10

5

Pred

ator

abu

ndan

ce

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abu

ndan

ce

1 5 10 15 20 25 30 35 40 45 50 55 60Time (weeks)

Figure 1.8.1 The predator–prey relationship of two mites

35ECOSYSTEMS

SUMMARY 1.8» The distribution and abundance of organisms is

influenced by a range of factors, which include the abiotic environment, the availability of resources, interaction with other species and interaction with members of the same species.

» An examination of variations in these factors within an ecosystem often provides an explanation for the

distribution and populations of organisms within the ecosystem.

» Members of different species within an ecosystem may have no significant impact on each other (see Table 1.8.1).

» Competition between species may result in elimination of one species or the species adapting to occupy distinct niches. In the short term, the abundance and distribution of at least one of the species are reduced.

QUESTIONS 1.81 List the four main interrelationships that influence the

distribution and abundance of organisms.2 State two types of relationship in which the organisms

are not harmed and give an example of each.3 State two types of relationship in which an organism is

harmed and give an example of each.

4 Use two specific examples to explain how relationships within species can influence their distribution and abundance.

5 In some predator–prey relationships, predators tend to prey more heavily on the young, weak and sick than on the strong and healthy. How

might such a relationship benefit the prey in the long term?

Table 1.8.1 Relationships between different species

RELATIONSHIP DESCRIPTION EXAMPLE

Mutualism Both organisms benefit Lichen (fungus and alga)

Commensalism One benefits; the other unharmed Anemone fish and anemone

Predation One organism eats another Dingo eats wallaby

Parasitism One organism lives in or on another, obtaining food from it Tick on dog

Competition Organisms compete for a limited resource Periwinkle and limpet compete for algae

Allelopathy One organism directly prevents the development of a competing organism by releasing toxins

Lantana secretions inhibit native plants

can be observed under laboratory conditions. In such experiments, the grain beetle Calandra is more successful than beetle Rhizopertha. Where they coexist, this results in a decrease in the Rhizopertha population. If competition between species continues in an ecosystem, one of the species can be eliminated from the area. In the long term, this can result in the extinction of the less successful species.

Over long periods, organisms evolve and adapt to their environment. Competition is one pressure in the environment that influences the evolution of organisms.

Partly as a result of competition, organisms evolve to occupy a particular niche within each ecosystem. An organism’s niche in an ecosystem results from a combination of the abiotic and biotic factors the species uses in its habitat. As a result of competition and evolution, organisms of different species do not occupy the same niche in the same ecosystem. The black periwinkle (Nerita) and the limpet (Cellana) feed on the same food resource and share the same environment in the same ecosystem but they occupy different niches because they feed in different ways.


6 State whether the situations described below are: (i) allelopathy (ii) mutualism (iii) commensalism (iv) competition (v) parasitism (vi) predator–prey relationships. (More than one answer may be chosen.) (a) The pollination of orchids by bees as they search

for nectar. (b) The killing of lyre birds by feral cats. (c) The digestion of wood in the gut of termites by

microorganisms. (d) The infection of humans by the malaria

plasmodium. (e) The building of nests in trees by magpies. (f) Water moccasin snakes dwelling beneath trees

where herons nest, eating fledglings that fall from the nests but preventing egg-eating predators from climbing the trees to raid the nests.

7 Describe two different types of relationship you have observed in your environment.

8 (a) Biologists think that relationships should not be called detrimental. Why might it be wrong in biology to call a predator–prey relationship detrimental?

(b) The word ‘allelopathy’ comes from two Greek words—allos meaning other and pathos meaning suffering. Do you think allelopathy is a good term to describe the relationship between lantana and the native plants it inhibits?

9 The graph (see Figure 1.8.3) shows the population change in duckweed in an aquarium. It is hypothesised that predation by water snails is limiting population size. Briefly outline an experiment to test this hypothesis. Redraw the graph to show how it would appear if the results:

(a) supported the hypothesis (b) refuted the hypothesis.

10 Figure 1.8.4 shows the population graphs of a number of organisms: a, b, c, d and x.

If x is the prey, which organism is most likely to be its predator? Explain.

11 Figure 1.8.5 shows populations of two paramecia grown under laboratory conditions.

(a) Explain the decrease in Paramecium caudatum population when it coexists with P. aurelia.

(b) Suggest why P. caudatum is not extinct.

140

120

100

80

60

40

0 1 2 3 4 5 6 7 8

Abun

danc

e

Time (weeks)

Figure 1.8.3 Changes in duckweed population

Abun

danc

e

a

bx

c

d

Time

Figure 1.8.4 The abundance of organisms a, b, c, d and x

37ECOSYSTEMS

0 2 4 6 8 10 12 14 16Days

Rela

tive

popu

latio

n de

nsity

Combined cultures

Separate culturesP. aurelia

P. caudatum

P. aurelia

P. caudatum

Figure 1.8.5 Competition between paramecium

12 Two types of barnacles often live in the same ecosystem. These are the brown barnacle (Chthamalus) and the grey barnacle (Balanus). Figure 1.8.6 shows a typical distribution of these barnacles on rocks. The grey barnacle is thought to be unable to survive as high on rocks as the brown barnacle because it is less tolerant of dry conditions. Develop a hypothesis to explain the distribution of the barnacles shown. Suggest one way in which you could test this hypothesis.

(a)

ocean

low tide

high tide

greybarnacles

(b)

ocean

low tide

high tide

brown barnacles

(c)

oceanlow tide

high tide

brownbarnacles

grey barnacles

chth

amal

usba

lanu

s

Figure 1.8.6 Distribution of barnacles. (a) Distribution of the grey barnacle in the absence of the brown barnacle. (b) Distribution of the brown barnacle in the absence of the grey barnacle. (c) Distribution of the grey and brown barnacles in co-existence


PRODUCERS AND CONSUMERSPlants are called producers because they use light energy to produce organic substances from the material they take in from their physical surroundings. Therefore, plants provide the initial food source on which all organisms depend for their matter and energy needs. In this way, plants provide the foundation on which a community is built.

Animals eat or consume other living things. Therefore, they are called consumers. An organism that feeds on plants is a first-order consumer. An organism that feeds on a first-order consumer is called a second-order consumer, and so on. Consumers that break down or decompose dead organisms are called decomposers. Many bacteria and fungi are decomposers. For example, a wallaby is a first-order consumer because it eats grass; a dingo, which eats the wallaby, is a second-order consumer; and the bacteria that bring about the decay of the dead wallaby and dingo are decomposers.

FOOD CHAINSWith the exception of plants, all organisms in a community obtain their material and energy needs from their food. Therefore, a description of the feeding patterns within a community actually indicates the direction in which energy and matter are transferred through the community. This can be achieved by drawing a flow chart indicating who feeds on whom. When this follows a single line without branching, it is called a food chain (see Figure 1.9.1). In a food chain, the arrow shows the direction in which the energy and matter flow. Hence, the arrow always points away from the organism that is the food and towards the animal that is eating or consuming it.

From the food chain shown in Figure 1.9.1, you should be able to see that the consumers occupy different levels. The level occupied by a consumer is referred to as a feeding or trophic level. First-order consumers occupy the first trophic level; second-order consumers occupy the second trophic level, and so on.

Figure 1.9.1 Producers and consumers in a food chain

Students learn to:» describe the role of decomposers in ecosystems» explain trophic interactions between organisms in an ecosystem,

using food chains, food webs and pyramids of biomass and energy.

Food webs1.9

producer first-order consumer second-order consumer

grass wallaby dingo

39ECOSYSTEMS

energy and matter through a community. The availability and flow of energy and matter have a major bearing on the structure and make-up of the community. Therefore, any alteration to the food web in a community may have far-reaching consequences. Hence, food webs can often be used to predict and explain the effects of changes within the community. For example, a farmer may want to eliminate foxes from the community because they prey on the sheep (see Figure 1.9.2). However, from the food web it can be seen that the destruction of the fox population may not be in the farmer’s best interests. The elimination of foxes could also lead to an increase in the population of pests (i.e. insects, mice and rabbits). These may, in turn, eat more grass and reduce the amount of fodder available to sheep. It may be that the presence of foxes in the ecosystem actually increases the productivity of the farm. In this way, food webs provide information that can help in the management and preservation of ecosystems.

Consumers can also be described according to the type of food they eat. Animals that eat plants are herbivores. Those that eat other animals are carnivores, and organisms that eat both plants and animals are omnivores. However, this system is not precise because omnivores and carnivores can occur at a number of different levels.

CONSTRUCTING FOOD WEBSThe feeding patterns in communities are complex. Therefore, they can never be described by a single food chain. The energy flow through a community actually occurs through a complex network of interconnected food chains called a food web (see Figure 1.9.2).

Food webs can be drawn in a variety of ways but to ensure quick, effective communication, it is convenient to follow a consistent pattern. When drawing a food web, the producers are usually placed at the bottom; the consumers are generally grouped according to their trophic level and placed in order from lowest to highest level up the page (see Figure 1.9.2). Because some organisms often occupy more than one trophic level, it is not always possible to adhere strictly to this pattern. The hawk, for example (see Figure 1.9.2) is a second-order consumer because it eats mice and a third-order consumer because it also eats birds. It therefore occupies both the second and third trophic levels.

Sometimes it is difficult to construct a food web because it is not always easy to observe an organism feeding.

USING FOOD WEBSFood webs are constructed to help us to understand how a community functions. They provide a concise description of the feeding patterns, which determine the flow of

Figure 1.9.2 A simplified food web

insects mouse rabbit sheephoneyeater

emu wren fox human

hawk

grassshrubs

Figure 1.9.3 Stable and unstable biomass pyramids

producers

Key:

herbivores

carnivoresunstable

stable

unstable unstable


ENERGY PYRAMIDSEnergy pyramids show the amount of energy at each trophic level in a community. They are similar to biomass pyramids because energy is transferred throughout a community as food. The lower the organism on a food chain, the more energy it has available to it. Figure 1.9.4 compares the energy pyramid of a human who is a vegetarian with a human whose diet consists only of meat. As at least 10% of the energy is lost at each trophic level, the vegetarian human makes much more efficient use of the energy available in the ecosystem than the human carnivore. Note that the human carnivore requires approximately ten times the energy in producers as the human as vegetarian. This has implications for the population of humans on Earth. The human population that can be supported on Earth is very much affected by human diet. If humans were to consume more plants and less meat, then the Earth could provide food for a larger human population.

INVESTIGATION 5 Food webs

BIOMASS PYRAMIDSJust as the flow of energy through an ecosystem is an important aspect of an ecological study, so too is the transfer of matter within an ecosystem. The total amount of mass in a community is called its biomass. Since matter is lost from the community at each trophic level, the biomass of the producers is usually greater than that of the first-order consumers and their biomass is, in turn, greater than that of the second-order consumers, and so on. This trend can be readily seen in biomass pyramids, which show the biomass of the organisms at each trophic level. The biomass of organisms is usually expressed as a percentage of the community’s total biomass (see Figure 1.9.3).

This allows us to compare the amounts of matter at each trophic level and indicates the efficiency with which matter is transferred through the community. Furthermore, because energy is transferred through the community as chemical energy in matter, it also indicates how efficiently the energy is being transferred.

The normal pattern of a biomass pyramid may occasionally be altered for a short time. Disease or drought can sometimes rapidly decrease the plant biomass. When this occurs, the consumer biomass may represent a larger than normal proportion of the community biomass for a short time (see Figure 1.9.3). However, the small plant biomass would not be able to provide sufficient energy or matter to support the consumers. This biomass pyramid is therefore unstable and many consumers typically die off or emigrate. Eventually, the characteristic stable biomass pyramid shape reappears (see Figure 1.9.3).

Food webs describe the direction of flow of energy and matter. Biomass pyramids show the amount of matter at each trophic level. Energy pyramids show the amount of energy at each trophic level. Because they provide different information about an ecosystem, biomass pyramids and food webs are best used together to describe the energy and matter transfer through a community.

(a)

(b)

cornbeans wheat apples

human

human

cattle

sheep

chicken

corn wheat grass

pigs

Figure 1.9.4 Energy pyramid of a human (a) vegetarian; (b) carnivore

SUMMARY 1.9» Plants are producers. Producers make the organic

materials on which all other organisms depend for food.» Animals are consumers. Consumers obtain food from

other organisms. They obtain energy and matter from the organisms they eat.

» Organisms that break down dead organisms and the waste products of organisms are decomposers.

» Many bacteria and fungi are decomposers. Decomposers are consumers.

» A food chain or web is a flow chart showing the feeding patterns within a community.

» Food chains and food webs show the flow of energy and matter through a community.

p56

41ECOSYSTEMS

» A food web is made up of a set of interconnecting food chains.

» Food webs can be used to explain and predict changes in the community.

» Biomass pyramids usually indicate the relative amount of matter in the organisms of a community.

» Energy pyramids indicate the relative amount of energy transferred to each trophic level.

» In a stable community, biomass and energy decrease rapidly as the trophic level increases.

» Biomass and energy pyramids can be used to predict and explain changes in a community.

QUESTIONS 1.91 Define the following terms: (a) producer (e) carnivore (b) consumer (f) omnivore (c) decomposer (g) biomass. (d) herbivore2 State whether the organisms listed below are (i)

producers, (ii) consumers, (iii) decomposers, (iv) herbivores, (v) carnivores or (vi) omnivores:

(a) sheep (f) Tasmanian devil (b) grass (g) bread mould (c) carrot (h) kangaroo (d) human (i) mushroom (e) wattle (j) worm.3 Draw a simple food chain for a human who only

eats beef.4 Which of the biomass pyramids in Figure 1.9.5 is most

likely to represent the biomass in a stable ecosystem?

5 Contrast the information about a community conveyed by a food web, a biomass pyramid and an energy pyramid.

6 Draw a food web for a community in which periwinkles and limpets feed on seaweed, octopuses feed on crabs, crabs feed on periwinkles and limpets, starfish feed on limpets, seals eat crabs, and octopuses and seagulls eat crabs and starfish.

7 On an excursion, a group of biology students observed a community and collected the following information. Use it to construct a food web.

During the day, parrots were seen feeding on grass roots. New Holland honeyeaters took nectar from banksias. Scale insects were found on the bark of young banksias, tea trees and eucalypts. Bees visited a variety of plants including banksias, tea trees and eucalypts. Wallabies were seen grazing on patches of grass in the woodland. At night, sugargliders licked the sap from eucalypts and competed with ringtail possums for banksia nectar. The house mouse ate grass seeds and scraps left over from visitors on picnics. The Antechinus preyed on the house mouse and small beetles that were commonly found nibbling grass. Lyrebirds also fed on beetles they found when scratching the ground. Yabbies abounded in small ponds where they scavenged on the dead and decaying material (detritus) that settled to the bottom. Foxes and quolls were not sighted, but their droppings were collected and found to contain the following:

» Fox droppings—beetle exoskeletons and wings, yabbie shells, house mouse and Antechinus fur.

» Quoll droppings—parrot feathers and house-mouse fur.8 Consider the information in the food web from question 7. (a) Name the producers. (b) State the consumer level of the house mouse. (c) Name an organism that occupies more than one

trophic level. (d) State one short-term consequence of poisoning

the insects. (e) State which organisms would have the highest

biomass. (f) State which organisms in the food web would be at

the greatest risk from biomagnification of poisons.9 Draw a possible biomass pyramid for the community

described in question 6.10 In a lake, for every 1000 kilojoules (kJ) of light energy

converted into carbohydrate by algae, small aquatic animals obtain about 150 kJ of energy. Of this 150 kJ, 30 kJ is transferred to smelt. Trout feeding on smelt obtain about 6 kJ of energy. If you eat the trout, you obtain only 1.2 kJ of energy from the trout.

(a) Draw a food chain for this community. (b) Draw an energy pyramid for this community.

Figure 1.9.5 Biomass pyramids

C

B

A


Students learn to:» identify the impact of humans in the ecosystem studied.

Human impacts on ecosystems1.10

Humans have an impact on their environment. In this they are not unusual. However, what is unusual is that the changes have been rapid and widespread. Modern affluent societies place huge demands on the resources of the Earth’s ecosystems. High levels of consumption result in high levels of waste and pollution. Ecosystems are often degraded or eliminated. Forests have been cleared for timber and agriculture. Other ecosystems have been destroyed because they were favoured dwelling places for humans. Fragile estuaries and coastal sand dunes, for example, provide homes with water views. Humans have moved throughout the Earth’s continents and islands. Our transport is rapid and covers huge distances. Organisms that once were isolated are now faced with species that humans have introduced from other continents. In Australia, introduced foxes, rabbits, feral cats and pigs have preyed on or competed with native species, damaging the complex fabric of ecosystems. All these activities reduce the range, distribution and species diversity of natural ecosystems.

Most humans have changed from hunters and gatherers to being members of agricultural and then urban societies. As hunters and gatherers, our activities had relatively little impact on ecosystems. By contrast, agricultural and urban societies have greatly disturbed ecosystems, altering the natural flow of energy and recycling of matter (see Table 1.10.1).

Table 1.10.1 Comparison of disturbed and undisturbed ecosystems

URBAN AGRICULTURAL NATURAL

Diversity Little; humans dominate Little; single crop species or animal dominate

Great

Complexity/stability Simple, unstable imbalance of animals over plants

Simple, unstable monocultures

Complex, stable

Energy input Mainly fossil fuels, nuclear, hydroelectric

Mainly light and fossil fuels Light only

Energy use Excessive burning with rapid heat output and energy loss—inefficient

Mainly photosynthesis and respiration with gradual heat output and energy loss

Matter recycling Very inefficient, little recycled Inefficient, some recycled Efficient, recycled

COMPARISON OF THE EFFICIENCY OF DISTURBED AND UNDISTURBED ECOSYSTEMS

Recycling of matterIn natural ecosystems, matter is recycled by decomposers. There is no long-term net loss of materials from the ecosystems. They are therefore self-sustaining. Agricultural ecosystems are constantly suffering a loss of matter: crops are harvested, lambs and cattle slaughtered. They are transported out of agricultural ecosystems into urban ones. The urban ecosystem is therefore constantly gaining

43ECOSYSTEMS

Energy useIn natural ecosystems, the main energy input is light from the sun. This is absorbed by plants, converted into chemical energy and used slowly over long periods of time by plants and animals. This energy is gradually changed into heat energy and released. In urban ecosystems, fossil fuels provide a large component of the energy input. When they are burnt, the result is a rapid release of heat energy.

Both urban and agricultural ecosystems are unstable. In agricultural ecosystems, diseases can spread rapidly and destroy virtually all the vegetation in an area because vast areas are dominated by a single species. Similarly, insect pests that feed on crops can often reach plague proportions.

In agricultural and urban ecosystems, where there are few species, food webs are very simple. Simple food webs are unstable because there are few alternative food supplies if one is lost. Natural ecosystems are diverse and more stable because they have complex food webs.

Because urban and agricultural ecosystems are simple and unstable, they require a very large energy input to maintain them. This energy is used for such activities as clearing and preparing land, planting crops, building dams, supplying insecticides and fertilisers, and transporting food and waste.

POLLUTIONHuman activities produce a variety of wastes that can contaminate ecosystems. These wastes pollute the environment and may degrade the habitat of other species and humans themselves.

matter from the agricultural ecosystem. The agricultural ecosystem often requires frequent applications of minerals from fertilisers or careful crop management to replace the lost nutrients.

Soil erosion resulting from agricultural practices is regarded by many as the most important conservation issue in Australia for the twenty-first century. Indeed, vast areas of Australia are at risk of becoming deserts (see Figure 1.10.1). It has been estimated that soil degradation costs approximately $600 million a year in lost agricultural production. We can only guess at the cost of its impact on the natural ecosystem.

In the urban ecosystem, the influx of matter results in the production of massive amounts of waste. Some wastes contain contaminants that pollute the environment. Most waste is often not recycled within the ecosystem but is typically dumped into natural ecosystems. In Sydney, most of the waste sewage is dumped into the ocean, where it damages beaches and aquatic ecosystems before being decomposed.

Even the air is imported into urban ecosystems from natural and agricultural systems because there are too few plants in cities to recycle the oxygen from the carbon dioxide produced by the animals and the burning of fossil fuels. Indeed, in recent times the production of carbon dioxide has outstripped the ability of the constantly decreasing natural ecosystems to convert the carbon dioxide into oxygen. This imbalance has resulted in an increase in the concentration of carbon dioxide in the atmosphere, causing the greenhouse effect, which many scientists claim is responsible for a gradual rise in the temperature of the Earth’s atmosphere.

very high

high

Key:

moderate

low

Figure 1.10.1 (a) Areas at risk of desertification in Australia. (b) Human activity is making some deserts bigger

(a) (b)


Most pollution is caused by humans from developed countries. Pollution is the result of our consumption of goods. Agriculture, which provides our food, and the bleaching of the paper on which you write, for example, can contaminate rivers and streams. The industries that supply you with the things you want, such as a car, also pollute the environment. These contaminants may pollute the water systems, the air and soil. The sources and types of water and air pollution are many. Some of these are shown in Table 1.10.2 and Figure 1.10.2. If you look carefully at the data in Table 1.10.2 you will see that transport is a major cause of air pollution. If you travelled by bus or car to school you contributed to this pollution. Even if you went to school by train, the electricity used to drive the train may have been produced by burning coal, which pollutes the air.

BIOMAGNIFICATIONFood webs can be used to predict the flow and possible long-term effects of contaminants that pollute an ecosystem. The concentrations of some pesticides, such as DDT, and heavy metals, like lead, mercury and cadmium, increase along the food chain; that is, higher order consumers tend to have higher concentrations of these

Table 1.10.2 Air pollution

POLLUTANT POSSIBLE HARMFUL EFFECTS MAJOR NON-NATURAL SOURCE

Particulates: smoke, dust, grit Corrosion and deterioration of building materials; eye, nose and throat irritation

Combustion of fossil fuels; motor vehicles; incinerators; industries; road construction etc.

Sulfur dioxide Formation of acid rain; corrosion; chest irritation; bronchitis

Combustion of fossil fuels; smelting of mineral ores

Carbon monoxide By binding with haemoglobin in the blood, oxygen absorption is reduced—may be fatal; impaired nerve functions; heart disease

Combustion of fuels

Nitrogen oxides Formation of acid rain, which is formed when nitrogen oxides combine with water in the atmosphere; plant growth retarded; corrosive; eye and throat irritation

Motor car engines

Ozone Irritation and disturbed functions of eyes, nose and lungs; death of leaves of plants; damage to rubber and textiles

Reaction between oxygen and nitrogen in the air

Hydrocarbon vapours Retarded plant growth; abnormal growth of buds and leaves; carcinogenic

Motor car engines; solvents in paints and dry-cleaning

Lead compounds Toxic; reduction of brain function Motor car exhaust; smelters

Radioactive materials Increased risk of mutation; cancer; genetic disturbances

Nuclear weapons; radioactive waste dumps

Peroxacetyl nitrate (PAN) Plant leaves attacked; eye irritation; lung functions disturbed

Chemical changes in the atmosphere due to the sun’s action on other pollutants

Figure 1.10.2 Source of water pollution. Research two of the problems identified to outline the cause, effects and possible solutions

Cities located on coasts may pipe sewage into ocean after only minimum treatment.

Landfill is often made up of dangerous chemicals large urban centres generate huge quantities of nutrient-rich effluent; other pollutants are detergents, oils from motor vehicles, soil from building blocks.

45ECOSYSTEMS

substances in their tissues than lower order consumers. This occurs for two reasons. First, these substances are only broken down very slowly and therefore accumulate in an organism’s body tissues over its lifetime. Second, the transfer of energy from one organism to the next by feeding is inefficient. Therefore, a predator must eat large quantities of prey to supply its energy and material needs.

While the energy transfer is such that the predator might only obtain 20% of the energy available in its food, it unfortunately accumulates almost all the DDT and heavy metals that were taken in by its prey. In this way the concentration of these substances is magnified along the food chain. This is known as biomagnification.

This biomagnification of DDT has resulted in a decline in the number of offspring produced by some birds of prey, including herring gulls, falcons, eagles and ospreys. These birds are higher order consumers. The concentration of DDT in these birds may be 250 times that in the non-living surroundings. Such high concentrations of DDT seem to prevent the formation of eggs or result in the production of eggs with thin, brittle shells, which tend to break prematurely during brooding.

In aquatic ecosystems, where food webs are often very complex and food chains can be very long, magnifications 80 000 times greater than the non-living surroundings have been observed. In Japan, the biomagnification of

Precipitation may fall through polluted air, dissolving atmospheric pollutants.

Agricultural yields are boosted by the addition of fertiliser; run-off from these can cause bacterial, algal and plant blooms in river systems.

Agricultural practices frequently involve the use of toxic chemicals for pest and weed control. These may become dissolved in surface run-off and transported to rivers.

Logging practices may expose soil to erosion.

Clearing increases soil erosion, leading to sedimentation of streams.

Mining and quarrying may cause sedimentation problems.

algal bloom (cyanobacteria)

Pollution from industry is extensive and often involves toxic wastes, such as heavy metals.

Irrigation may mobilise salt and lead to salinisation of rivers (and soil).

Aerial spraying of pesticides and herbicides may directly contaminate water.


» national and international agreements to reduce energy consumption, promote recycling, prevent dumping of wastes and reduce the destruction of natural ecosystems

» education to promote lifestyle changes that reduce consumption and encourage recycling

» preventing the import and accidental release of introduced species

» maintaining a range of habitats to promote diversity (e.g. national parks and reserves)

» regenerating natural ecosystems where they have been destroyed or degraded

» farming native animals and crops rather than introduced species

» establishing sustainable quotas to reduce the impact of the removal of plants (e.g. trees for timber) and animals (e.g. fish) taken from natural ecosystems.These and other strategies are easy to outline but they

are difficult to implement because the management of the world’s resources not only is a matter for biology, but also involves a complex set of interacting influences including politics, economics and culture.

The difficulties involved in developing an agreed, worldwide strategy to reduce human impact on ecosystems have promoted an emphasis on actions by each individual rather than governments alone.

mercury released from industry into Minnamatta Bay resulted in the deaths of fifty-two people. These people regularly ate fish from the bay over a long period and suffered mercury poisoning. Cats, another higher order consumer in the community, also suffered. Mercury poisoning attacks the nervous system, so these diseased cats often shook and jittered uncontrollably. Hence, the illness became known as the ‘disease of the dancing cat’. The levels of mercury and other heavy metals in fish at Australian fish markets are regularly monitored. In Sydney, for example, this thorough testing has occasionally resulted in swordfish, a higher order consumer, being withdrawn from sale because of heavy metal concentrations above recommended levels. A knowledge of food webs allows the types of fish that are at risk to be identified and helps to ensure that contaminated fish are not sold.

HUMAN WANTS AND SUSTAINING ECOSYSTEMS—FINDING A BALANCEThe high energy demands and lack of recycling in human-dominated ecosystems make them unsustainable. Strategies are required to reduce demand and increase recycling and to maintain remaining natural ecosystems. Strategies to achieve this include:

SUMMARY 1.10» Humans have had a range of impacts on ecosystems.

These include the destruction of ecosystems (e.g. clearing forests and estuaries), introduction of species that compete with or prey on native species, and pollution of ecosystems with contaminants that affect the survival of organisms.

» The use of energy and matter in most human-dominated ecosystems in developed countries is not sustainable.

» A variety of strategies can be used to balance human activities and needs in ecosystems to conserve, maintain and protect the quality of the environment, but these are difficult to implement due to economic, cultural and political pressures.

» Energy use and flow in undisturbed ecosystems is

more efficient than energy flow through disturbed ecosystems (e.g. agricultural and urban ecosystems).

» Matter recycling in undisturbed ecosystems is more efficient than matter recycling through disturbed ecosystems (e.g. agricultural and urban ecosystems).

QUESTIONS 1.101 List three main ways in which humans have a

detrimental impact on ecosystems. For each of these, suggest one way in which the impact could be reduced.

2 How is the flow of energy in natural ecosystems different from that in disturbed ecosystems?

3 How is recycling of matter in disturbed ecosystems different from that in natural ecosystems?

4 Suggest two reasons why it is difficult to implement

47ECOSYSTEMS

strategies to protect the quality of the environment.5 Identify one way in which you could reduce your

detrimental impact on the environment.6 David Suzuki once said that if you really want a

species to survive, eat it. What might he have meant by this?

7 The list below indicates some strategies humans employ to reduce their impact on the environment:

» maintaining treed areas in pastures » contour ploughing » recycling » biological control » the Kyoto agreement. Research two of these and explain how they reduce

human impact on ecosystems.8 Table 1.10.3 shows the energy consumption per capita

in a variety of countries. Graph energy consumption against population.

Briefly comment on any trend you can infer from the graph.

Is human impact on ecosystems mainly a result of overpopulation? Suggest one other factor that seems to influence human energy consumption.

9 Some poisons used to kill insect pests in lawns are sprayed at night because they break down quickly when exposed to light. These poisons are extremely toxic and can kill birds even in small concentrations. When used correctly, why might these very toxic poisons often cause less damage to the community than less poisonous substances such as DDT and heavy metals? Explain.

10 Research one agreement, activity or event to reduce detrimental human impact at the following levels:

» international » national » local area or local government » individual.

Table 1.10.3 Human energy consumption per person, selected countries (2003)

COUNTRY POPULATION (MILLIONS)

ENERGY PER PERSON (GIGAJOULES)

Bangladesh 147 6.76

Nigeria 134 32.63

India 1069 21.52

Indonesia 220 31.81

Brazil 176 44.84

China 1289 47.81

Turkey 71 46.44

Japan 128 169.70

Germany 83 176.53

United States 292 327.38

Australia 20 240.38


Investigations 1–5 should be carried out in two different ecosystems or in an ecosystem that contains a variety of vegetation types. In this way, comparisons can be made and the important factors contributing to the existence and maintenance of the ecosystem can be more easily identified.

Ideally, one of the two ecosystems should be in your local area so that frequent visits are possible. Name the ecosystems and communities studied.

The aim of this sequence of practical work is to study an ecosystem and identify interrelationships between living and non-living things and interrelationships between living things in the area.

Take care to ensure that the ecosystem is disturbed as little as possible by your investigations.

INVESTIGATION 1: MEASURING PHYSICAL CHARACTERISTICS OF AN ECOSYSTEM, AND OBSERVING INCIDENCE OF HUMAN IMPACTStudents:» observe and measure a variety of abiotic characteristics in ecosystems and relate them to the distribution of organisms

1 INVESTIGATIONS» tabulate data, calculate means, graph changes against time, evaluate the variability in measurements» identify the impact of humans in the ecosystems studied.

InformationAn examination of the physical characteristics of an ecosystem can provide a basis for understanding the interrelationships that exist within an ecosystem. In particular, it can help to explain the existence and extent of the ecosystem as well as the distribution and abundance of organisms within it.

The aims of this exercise are to provide experience in the use of a wide range of procedures that can be used in your field work to study physical environmental factors, and to use the data collected to explain the distribution of organisms in the ecosystems studied.

Ideally, these abiotic factors should be measured over a long period of time. Brief visits to ecosystems can sometimes provide very misleading data. Climatic factors, in particular, are best measured over many years or at least over the seasons. If it is not possible to visit your study area regularly throughout the year, additional data can sometimes be obtained from students who have studied the ecosystem in previous years.

35

30

25

20

15

10

5

0

1 2

3

4

5

woodland bare rock closed heath woodland closed forest

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85Distance (m)

Heig

ht (m

)

Key:

woodlandeucalypt

foresteucalypt

shrubs

ferns

grass

1,2,3,4,5sitesfor datacollection

Figure I1.1 Vegetation transect

49ECOSYSTEMS

Recording data» Make measurements at a number of randomly selected

sites along a transect (see Investigation 2) or at randomly selected sites throughout the area.

» On the transect diagram of the area, mark the sites where recordings were made (see Figure I1.1).

» Collect data on as many days as possible.» Indicate the time and date when the data were collected.» Construct a table to record your data (see Tables I1.1

and I2.1).

PART A TEMPERATURETemperature range

Materials» maximum/minimum thermometer

Method1 Use the maximum/minimum thermometer to measure

the maximum and minimum temperature each day.2 Collect data at a set time each day (e.g. 9 a.m.) and reset

for the following day.3 Record temperature range for each day and month.4 Calculate an average maximum and minimum

temperature for each month for which you have data.5 Use a graph to present maximum and minimum

temperature data.

Atmospheric temperature

Materials» thermometer

Method1 Use the thermometer to measure the temperature at

regular intervals throughout the day in the shade and in full sun.

Soil temperature

Materials» soil thermometer or laboratory thermometer

Method1 If you have a soil thermometer, push it into the ground

to its maximum depth. If you are using a laboratory thermometer, dig a narrow

hole almost as deep as the thermometer. Gently lower the thermometer into the hole and refill the hole, leaving the tip of the thermometer exposed.

2 Leave the thermometer in the soil for about 3 minutes.3 Check and record the temperature.4 Repeat as early as possible, in the middle of the day, and

as late as possible.

Questions1 Were there differences in the temperature recorded in the

ecosystem?2 Would it be more difficult for an organism to adapt to

an ecosystem with a varied temperature or to one with a fairly constant temperature? Why?

3 How does temperature influence water availability?4 How does temperature influence the water requirements

of organisms?5 Did the soil temperature vary as much as the

atmospheric temperature?6 Why do some animals live in burrows?

PART B LIGHT INTENSITYMaterials» light meter

Method1 Use the light meter to measure the light intensity at a

range of heights above the ground (e.g. ground level, hip level and eye level).

2 Repeat at set times in the morning, at midday and in the afternoon.

3 Rate the light intensity as very high, high, moderate or very low.

Questions1 Was the amount of cloud cover similar when the

measurements were made?2 (a) Were there differences between the light readings

in the ecosystem? (b) How can you account for the differences?

Table I1.1 An example of a table to record temperature data

TEMPERATURE (°C)

DATE TIME MAXIMUM MINIMUM

1/6/09 9 a.m. 20 8

2/6/09 9 a.m. 20 11

3/6/09 9 a.m. 15 7

4/6/09 9 a.m. 10 4


3 Was there less light available at ground or hip level than at eye level? How might this influence the growth of shrubs and grasses?

PART C RELATIVE HUMIDITYMaterials» wet and dry bulb thermometer (psychrometer)» relative humidity conversion chart

Method1 Use the wet and dry bulb thermometer and the

conversion chart to measure the relative humidity at regular intervals throughout the day.

2 Measure the humidity at different heights above the ground.

Questions1 (a) Were there differences between the humidity

readings in the ecosystem? (b) Were some areas generally more humid than the

other areas?2 How might humidity affect the rate of water loss from

organisms?3 Use a graph to record humidity for the period of your

study.

PART D RAINFALLMaterials» rain gauge

Method1 Use a rain gauge to measure rainfall each day.2 Collect the data at a set time each day (e.g. 9 a.m.) and

empty it for the following day.

Questions1 Were there differences in the rainfall in the ecosystem?2 How might rainfall affect other abiotic factors such as

humidity and soil moisture?3 How might rainfall influence the organisms in the

ecosystem?4 Research the mean annual rainfall and monthly or

seasonal rainfall in the ecosystems you studied. Graph the data to show the rainfall pattern over the year.

PART E WINDWind speed

Materials» anemometer or modified Beaufort scale (see Table I1.2)

Method1 Use the anemometer to measure wind speed at regular

intervals throughout the day.2 Measure the wind speed at different heights above the

ground (e.g. ground level, hip level and eye level).3 Note high and low readings if the wind is occurring in

gusts.4 Rate the wind speed as very high, high, moderate, low or

very low.

Wind direction

Materials» thin piece of cloth on a stick» compass

Method» Use the compass and cloth on a stick to determine the

wind direction.

Wind exposure

MethodRate the exposure to wind as very high, high, moderate, low or very low.

Questions1 (a) Were there differences between the wind readings

or exposure in the ecosystem? (b) Was one area more exposed to wind than the other?2 How might wind influence organisms in an ecosystem?3 (a) How might wind, rain and temperature interact to

make organisms colder? (b) What is meant by the chill factor?4 Was there any evidence of damage caused by winds

or of trees and shrubs leaning in a particular direction because of a pattern of prevailing winds?

5 Would trees find it more difficult to withstand high winds in areas with deep or with shallow soils? Explain.

Table I1.2 Modified Beaufort wind scale

OBSERVATION RATING

Smoke rises vertically or drifts gently; wind vane does not move.

very low

Wind felt on face; leaves rustle; wind vane moves.

low

Leaves and twigs constantly moving; raises dust; small branches move.

moderate

Large branches in motion; difficult to use umbrellas.

high

Whole trees swaying; twigs and leaves fall from trees.

very high

51ECOSYSTEMS

PART F SOILSoil pH

Materials» bottle, with holes in its lid, containing talcum powder or

barium sulfate» Petri dish» dropper bottle containing universal indicator» universal indicator pH colour chart

Method1 Collect a small sample of soil and place it on the Petri

dish.2 Sprinkle a layer of talcum powder (or barium sulfate) on

the soil.3 Add a few drops of universal indicator to the talc.4 Observe the colour and compare it with a colour chart to

find the pH.

Soil humus

Materials» trowel» 30 cm ruler

Method1 Carefully dig a hole in the soil.2 Use the ruler to measure the depth of the dark-coloured

topsoil layer.3 Observe the depth of the leaf litter and humus on top of

the soil.4 Rate the humus content as very high, high, moderate,

low or very low.

Soil moisture

(Use either Materials 1 or 2 and Methods 1 or 2.)

Materials 1» 1 strip of cobalt chloride paper per test

Method 11 Place a piece of dry (blue) cobalt chloride paper on a soil

sample.2 Note the time it takes to change from blue to pink.

(Cobalt chloride paper can be made by soaking filter paper in a cobalt chloride solution and then drying it. It should be kept in a dry, sealed container with some silica gel crystals.)

3 Rate the soil moisture as soggy, wet, damp, dry or very dry.

ORMaterials 2» plastic bag that can be sealed» glass Petri dish or evaporating dish» chemical balance» oven

Method 21 Collect a small soil sample.2 Place the sample in the plastic bag and seal it.3 In the laboratory, find the weight of the soil sample.4 Place it in the oven on low heat until it has dried out

completely.5 Reweigh the soil. (The difference between the weight

before and after heating provides a measure of the water content.)

Soil porosity

Materials» Petri dish» filter funnel» glass wool» 25 mL graduated measuring cylinder» beater or jar for water marked at 100 mL

Method1 Collect a sample of soil and thoroughly dry it on the

dish in the sun or in an oven on low heat.2 Pack a small amount of glass wool into the filter funnel.3 Gently pack some of the soil into the filter funnel on top

of the glass wool.4 Place the funnel over the graduated measuring cylinder.5 Add 50–100 mL of water and time how long it takes

for 10 mL of water to collect in the measuring cylinder. More water can be used if too little water passes through the soil.

(If you are going to compare soils from different sites, ensure that the same quantity of soil, water and glass wool is used for each test.)

6 Rate the soil porosity as very high, high, moderate, low or very low.

Soil mineral content

Materials» laboratory or commercial garden soil test kit. (Soil test

kits are available in most school laboratories or can be obtained from a plant nursery. These can be used to measure the content of a range of salts, including nitrates, sulfates and phosphates in soil.)


Method1 Follow the instructions given in the soil test kit.2 For each mineral, rate the soil as good, moderate or

poor.

Soil air content

Materials» small clear plastic jar or beaker» trowel

Method1 Place a sample of soil in a beaker of water and note the

rate at which air bubbles from the soil.2 When comparing different soils, use the same volume of

soil.3 Rate the soil air content as very high, high, moderate,

low or very low.

Questions1 Were there differences in the characteristics of the soils

in the ecosystem? Describe any differences.2 (a) Briefly explain how each of the soil characteristics studied might influence the organisms in the

ecosystem. (b) Was there any evidence that soil type influenced

the distribution of the vegetation types in the ecosystem?

3 How might soil porosity influence soil moisture content?4 (a) Was there evidence of rotting organic matter in

the soil? (b) How might this contribute to soil quality?5 You have measured many different abiotic factors in

your study. Others studying the same area might obtain data different from yours. How could you account for this variability in data? Consider a range of abiotic factors in your answer. Are some methods of measuring abiotic factors more accurate than others? Explain with examples.

PART G HUMAN IMPACTMethodWhile doing investigations in the ecosystem, record evidence of human impact, for example:» introduced species» erosion due to human activity» pollution.

QuestionHow might human impact influence the sustainability of the ecosystem studied?

INVESTIGATION 2: USING A TRANSECT TO STUDY THE DISTRIBUTION OF PLANTS

Students:» construct a transect to record data» describe and analyse the distribution of plants in an ecosystem» design a study to investigate factors influencing the distribution of plants in an ecosystem.

InformationIt is usually too time-consuming to show the position of every plant in an ecosystem on a map. However, it is relatively easy to show the distribution of the plants within a section of the ecosystem. One way of doing this is to record the plants along a cross-section or profile of the ecosystem. The line through the area along which this cross-section is taken is called a transect.

Materials» length of string marked with coloured adhesive tape at

5 m intervals (the string should be long enough to cross the area to be studied)

» compass» metre ruler» small stake (optional)

Method1 Select a compass heading that cuts across the

ecosystem.2 Tie the string to a rock, tree or stake.3 Walk through the ecosystem, gradually unrolling the

string. Use the compass to make sure that you are walking as near as possible to a straight line.

4 Draw vertical and horizontal axes on your page. Label the vertical axis ‘height’ and the horizontal axis ‘distance’ (see Figure I1.1). Mark out approximate units on the axes.

5 Draw a cross-section of the topography of your transect (see Figure I1.1).

6 At each 5 m interval along the string, note the plants that lie within 1 m along one side of the transect and estimate their height. (The plants need only be

53ECOSYSTEMS

identified in general terms, e.g. grasses, ferns, shrubs, trees. Bare rock or sand should also be shown.)

7 Use symbols to show these plants on the cross-section you have drawn (see Figure I1.1).

8 From the transect, identify sites where there appear to be different types of vegetation.

9 Number these sites on the transect.10 Measure and record the abiotic factors at these sites

and record the data in a table (see Table I2.1). (See also Investigation 1 for procedures.)

Questions1 Describe any variation in plant distribution you

observed.2 Try to explain these variations in plant distribution in

terms of: (a) variations in physical environmental factors (b) interrelationships between organisms.3 How might the variations in plant distribution influence

the distribution of animals? (For example, would tree- or grass-dwelling animals be able to inhabit all areas of the transect equally?)

4 Design an investigation to determine the factors that influence the distribution of one of the plants identified in the transect.

INVESTIGATION 3: USING QUADRATS TO MEASURE THE ABUNDANCE OF PLANTS IN AN ECOSYSTEM

Students:» use quadrats to study species abundance» describe and analyse the abundance of plants in an ecosystem» design a study to investigate factors influencing the abundance of plants in an ecosystem.

InformationThe aim of this exercise is to measure the abundance of a plant species within an ecosystem. Use either Method 1 or Method 2.

Table I2.1 Physical factors along the transect

PHYSICAL FACTOR SITES

1 2 3 4 5

Temperature (°C) max. min. soil

241323

2413—

241323

241323

241323

Relative humidity 54% 55% 59% 58% 82%

Wind speed direction exposure

moderateSWextreme

moderateSWhigh

moderateSWhigh

moderateSWhigh

——minimal

Light intensity eye level hip level group level

moderatemoderatelow

very highvery highvery high

very highvery highvery low

moderatemoderatevery low

lowlowvery low

Soil pH depth moisture humus air

6shallowdrylowmoderate

—none—very low—

5shallowsoggymoderatevery low

7shallowdampmoderatemoderate

7deepdamphighmoderate

Nutrients nitrates phosphates sulfates potassium

poormoderatemoderatemoderate

————

poorpoormoderatemoderate


goodgoodgoodmoderate


Materials» tape-measure or string marked at regular intervals with

adhesive tape» metre ruler

Method 11 Select the plant species of which you want to measure

the abundances.2 Choose a quadrat size suitable for the plant being

studied. (A tree may require quadrats of 10 m by 10 m or more. Grass may require quadrats of less than 1 m by 1 m.)

3 Note the size of the quadrat to be used.4 Use string with adhesive tape attached at appropriate

intervals, or a tape-measure, to mark out a square quadrat.

5 Count the plants that are members of the species under study.

6 Record the data in a table (see Table I3.1).7 Repeat steps 4–6 at a number of randomly selected sites

throughout the ecosystem or at sites along a transect.8 Estimate the total area of the ecosystem.9 Calculate the average number of plants per square

metre.10 To find the abundance, multiply the average number of

plants per square metre by the number of square metres in the whole ecosystem.

ORMethod 21 Use the transect from Investigation 2.2 In each 5 m interval along the transect, count the

number of plants of the species under study that are not more than 1 m away from one side of the string.

3 Record the data for each 1 m × 5 m rectangle (see e.g. Table I3.1).

4 Calculate the average.5 Estimate the total area of the ecosystem.6 Calculate the average number of plants per square

metre.7 To find the abundance, multiply the average number of

plants per square metre by the number of square metres in the whole ecosystem.

Questions1 Explain why the quadrat size chosen was appropriate.2 How could more accurate data be obtained?3 Would the same procedure be suitable for estimating

the abundance of bush rats in the ecosystem? Explain.4 (a) Did each quadrat contain a similar number of

plants? (b) How even does the distribution of these plants

appear to be? (c) If the abundance in each quadrat is very different: (i) how can these differences be explained?

Table I3.1 An example of plant abundance

ABUNDANCE DENSITY 25 m2

Sample number 1 2 3 4 5

Number of B. paludosa 12 10 5 13 10 10

Species under study: Banksia paludosaQuadrat size: 5 m × 5 m (i.e. 25 m2)Area of ecosystem: 5000 m2

Average number of B. paludosa per quadrat = 10

Average number per m2 = 10 25 m2

Abundance = average number of plants per m2 × area of ecosystem in m2

i.e. = 10 × 5000 m2

25 m2

= 2000

55ECOSYSTEMS

(ii) how should you report the abundance data in the ecosystem?

5 Design an investigation to determine the factors that influence the distribution of the plant species studied in this exercise.

INVESTIGATION 4: DISTRIBUTION AND ABUNDANCE OF ANIMALSStudents:» use tables to record field data» describe and analyse the abundance and distribution of animals in an ecosystem.

InformationThe distribution of animals within an ecosystem can be determined in a variety of ways. The distribution of invertebrates can often involve the trapping and killing of organisms such as insects. The aim of this exercise is to determine the distribution and abundance of a variety of animals with minimum disturbance of the ecosystem.

The procedures below can be carried out at a number of sites throughout the ecosystem. If they are carried out at regular intervals along a transect (see Investigation 2), you may be able to use data collected along the transect to help you to explain the distribution of animals. It may be necessary to move some distance from the transect line to avoid excessive disturbance of the area.

Materials» trowel» pair of gardening gloves» large sheet of white paper or cardboard» open tin can or small soil auger» sweep net» metal spatula or blunt knife

MethodNote any evidence of feeding patterns observed throughout this exercise, for use in Investigation 5.WARNING: Take care to avoid snakes, spiders and any insects that may sting or bite.

PART A LEAF LITTER1 Rake and turn the leaf litter in about 1 m2.2 Count the organisms present and identify them in

general terms.

3 Spread samples of leaf litter on white paper and watch for movement.

4 Record the data in a table (see Table I4.1).

PART B SOIL1 Remove the leaf litter from a small area.2 Press an empty tin can into the soil.3 Remove the can, lifting out the soil. If the soil does not

come out with the can, gently dig it out with a trowel.4 Spread the soil on a sheet of white paper.5 Count and identify organisms in general terms.6 Record the data in a table.

PART C ROTTING LOGS AND BRANCHES1 Use a trowel or stick to break open rotting logs or

branches.2 Count and identify the organisms in general terms.3 Record the data in a table.

PART D GRASSES, SEDGES AND SMALL SHRUBSFlying insects1 Using a sweep net, sweep the net in wide arcs with the

hoop just above the foliage.2 When the disturbed insects fly or jump in, turn the

handle so that the hoop folds up, closing off the opening to the net.

3 Count and identify the organisms in general terms.4 Record the data in a table.

Insects attached to plants1 Carefully examine the foliage of a range of shrubs and

grasses.2 Count and identify the organisms in general terms.3 Record the data in a table.

PART E BARK1 Use a metal spatula to lift small pieces of bark on

shrubs and trees.2 Count and identify the organisms in general terms.3 Record the data in a table.

Questions1 How could animal distribution and abundance be

measured more accurately?2 Many native mammals are nocturnal. How could these

be observed?


INVESTIGATION 5: FOOD WEBSStudents:» describe two trophic interactions found between organisms in the area studied» construct food chains and food webs to illustrate the relationships between member species in an ecosystem.

InformationWhen ecologists construct food webs, they often make detailed observations of organisms in the field over a long period of time, examine the stomach contents of dead animals and study animal droppings. With adequate reference materials, fur, feather and seed samples in stomach contents and droppings can usually be traced to the specific species of mammal, bird or plant that was eaten.

3 Were the animals evenly distributed across the different sites?

4 Try to explain the variation in distribution of at least two animals.

5 With reference to a specific animal, suggest how each of the following might have influenced its distribution and abundance:

(a) the availability of a resource (b) a physical environmental factor (c) an interrelationship with another organism.6 Design an investigation to determine the factors that

influence the distribution and abundance of an animal studied in this exercise.

Table I4.1 An example of an animal abundance and distribution record in leaf litter

ANIMALS OBSERVED SITE TOTAL

1 2 3 4 5

NUMBER OBSERVED

Skink 2

Spider A 1

Spider B 1

Amphipods 7

Native cockroach 1

White grub 1

Bull ant 3

Seed ant many

Slater 2

Comments

One skink lost its tail when disturbed.The amphipods were difficult to count because they jumped about very quickly.The white grub appeared to be an insect larva.The seed ants were moving very rapidly along a single line in great numbers. A nest was found near by.The slaters appeared to be dead.

57ECOSYSTEMS

The aim of this exercise is to construct a simplified food web. The exercise is best carried out while completing Investigations 1–3.

Materials» 10 plastic bags for droppings» dissecting needle» forceps» probe» Petri dish» dissecting microscope or hand lens» plastic gloves

Method1 Identify and record all the organisms you observe in the

ecosystem.2 Note any firsthand feeding you observe (e.g. honeyeater

feeding on eucalypt flowers, grasshoppers chewing on grass).

3 Note any secondhand evidence of feeding (e.g. half-eaten leaves, gnawed bark).

4 Collect animal and bird droppings.5 Pull apart droppings with probes, dissecting needle and

forceps.6 Examine the droppings’ contents under a dissecting

microscope or hand lens.7 Record the contents of the droppings in a table.8 Use the data collected and reference books to construct

a food web.

Questions1 List the types of food sources for which you would not

be able to find any evidence in animal droppings.2 List the types of materials that can be found in animal

droppings.3 Do animal droppings give an accurate view of the food

sources of animals? Explain.

MULTIPLE CHOICE1 The area of an ecosystem where members of a species are found is known as their: A distribution B biomass C habitat D abundance.2 Coral polyps often contain algae living within their tissues, which contribute to their spectacular

colours. The algae generally do not survive outside the polyp and the coral grows more slowly if the algae are not present. This association could be best described as:

A competition B commensalism C allelopathy D mutualism.3 The collective name for the members of a particular species living in an ecosystem is a: A population B habitat C family D community.4 The map in Figure E1.1 shows the distribution of the common brushtail possum. From this

distribution map, you could conclude that: A the abundance of the common brushtail possum is greater on the mainland than in Tasmania B the common brushtail possum is not evenly distributed throughout its range C changes in vegetation patterns have isolated populations of the common brushtail possum D none of the conclusions A, B or C is correct.

1 PRACTICE EXAMINATION QUESTIONS

Figure E1.1 Distribution of the common brushtail possum in Australia


59ECOSYSTEMS

5 The main role of bacteria in the ecosystem is to: A act as chemosynthetic producers B provide a food source for plankton-feeding aquatic animals C prevent overpopulation by causing disease D make minerals in dead organisms available to plants.6 Since people have been cultivating the land in Australia, the size of the deserts has been

increasing. Which of the following would be most likely to cause marginal crop or grazing lands to become permanent deserts?

A loss of nutrients to grazing animals B loss of minerals in harvested crops C erosion and loss of soil D insufficient use of organic fertilisers7 In a forest, five species of insect-eating birds are found. All of these species are able to survive.

One reason why all might be able to survive is because they: A eat the same type of insect B eat in different parts of the forest C have their populations kept in check by predators D feed off each other.8 The graph in Figure E1.2 indicates the loss of water by evaporation from three terrestrial

organisms. Which organism is most likely to inhabit a moist environment? A fly larva B crustacean C adult beetle D small lizard9 Figure E1.3 illustrates the appearance of birds in Kakadu National Park after fire. Which of the following birds would you most expect to arrive 4 days after a fire? A black kite B kookaburra C owl D galah

40

35

30

25

20

15

10

5

010 20 30 40 50 60

Temperature (°C)

Evap

orat

ion

rate

(mg/

cm2 /h

)

fly larva

smallcrustacean adult

beetle

smalllizard

1–3

min

1–3

days

1–3

wee

ks

3–4

wee

ks

Mor

e th

an4

wee

ks

Fire

Hot a

sh

Cold

ash

Suck

ers

Gras

s

Bird species

black kitewoodswallow

tree martin

pied butcherbirdgrey butcherbird

kookaburrared-backed kingfisher

forest kingfishertorresian crow

whistling kiteblack falcon

brown falcon

owlnight jar

magpie-lark

straw-necked ibis

red-tailed black cockatoo

partridge pidgeon

little corellanorthern rosella

galahquail

Figure E1.2 Evaporation of water from four animals Figure E1.3 Arrival of birds in Kakadu National Park after fire


10 Which of the following roles is not played by bacteria in an ecosystem? A matter recycling B energy recycling C nitrogen fixing D decomposition

SHORT ANSWER AND EXTENDED RESPONSE QUESTIONS1 The greenhouse effect results in the warming up of the atmosphere. This is mainly caused by

increasing concentrations of carbon dioxide in the atmosphere. From your knowledge of the carbon cycle:

(a) suggest two ways in which the greenhouse effect might be reduced (b) explain why some crop farmers see the increased carbon dioxide concentration as beneficial.

2 (a) What are figures (a) and (b) in Figure E1.4? (b) What information is conveyed by (a) but not by (b)? (c) What information is conveyed by (b) but not by (a)? (d) Identify the initial source of energy for this community.3 (a) What is a resource? (b) Briefly describe how a named resource affected the distribution of a named organism in an

ecosystem you have studied.4 (a) Identify the main role of decomposers in an ecosystem. (b) Give examples of two types of decomposers.5 A farmer decided to grow corn to feed his pigs, which he then sold. He argued that if he collected

the pigs’ droppings and used them to fertilise his corn, he could continue the process forever. (a) Explain the main flaw in the farmer’s reasoning. (b) What eventually happens to all the energy that enters this ecosystem?6 (a) Identify an ecosystem you have studied. (b) Describe the method you used to determine the abundance of an animal or plant. (c) Explain how the accuracy of your estimate could be improved.7 A student noticed that slaters appeared to be most abundant in moist, dark conditions where

humus was plentiful.

possum sheep rabbit

dingo

grasstree

(a)

(b)

possum sheep rabbit

tree grass

fox

dingo fox

Figure E1.4

61ECOSYSTEMS

(a) Write a hypothesis that attempts to explain the distribution of slaters in terms of one factor. (b) Design an experiment to test this hypothesis.8 A student made the following observations when studying a rock platform. Periwinkles, chitons and limpets grazed on green algae, which covered the rocks. The octopus

not only dined on small fish, which fed on zooplankton, but also competed with the starfish for limpets, periwinkles and mussels. The water abounded in phytoplankton and zooplankton. The zooplankton devoured the phytoplankton, while they themselves fell prey to the mussels and barnacles, which filtered the water to collect any microscopic organisms.

(a) Use this description to draw a food web for the community. (b) Identify a second-order consumer. (c) Identify one of the organisms that would be under the

greatest threat from biomagnification. (d) Explain one short-term consequence of the elimination of

mussels from the ecosystem. (e) Identify the organisms which would have the greatest

biomass in this community. Explain your reasoning.9 The graph shown in Figure E1.5 illustrates the annual Australian

catch of scallops. The arrows indicate the opening of new fishing grounds.

(a) Describe one trend you can infer from the data. (b) Assume you have been asked to manage the catch of

scallops. Suggest one strategy you would implement to ensure the catch could be sustained. Briefly outline how you would determine whether your strategy was successful.

10 Use the information presented in Figure E1.6 and Table E1.1 to account for the distribution of forest and heath.

11 Give an example of mutualism and explain how it is different from commensalism.12 During an investigation of an ecosystem, you studied evidence of human impact. Describe one

example of a human impact on an ecosystem, and explain how this impact has affected: (a) the diversity of species in the ecosystem (b) the sustainability of the ecosystem.

Scal

lops

cau

ght (

tonn

es)

Year1960 1970 1980 19901950

4500

4000

3500

3000

2500

2000

1500

1000

500

0

Great Oyster BayNorfolk Bay

Port Phillip BayNorth-east Tasmania

Lakes EntranceJervis Bay

Bass Strait

Figure E1.5 Annual Australian catch of scallops

35

30

25

20

15

10

5

0

1 2

3

4

5

woodland bare rock closed heath woodland closed forest

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85Distance (m)

Heig

ht (m

)

Key:

woodlandeucalypt

foresteucalypt

shrubs

ferns

grass

1,2,3,4,5sitesfor datacollection

Figure E1.6 Vegetation transect


Table E1.1 Physical factors along the transect

PHYSICAL FACTOR SITES

1 2 3 4 5

Temperature (°C) max. min. soil

241323

2413—

241323

241323

241323

Relative humidity 54% 55% 59% 58% 82%

Wind speed direction exposure

moderateSWextreme

moderateSWhigh

moderateSWhigh

moderateSWhigh

——minimal

Light intensity eye level hip level group level

moderatemoderatelow

very highvery highvery high

very highvery highvery low

moderatemoderatevery low

lowlowvery low

Soil pH depth moisture humus air

6shallowdrylowmoderate

—none—very low—

5shallowsoggymoderatevery low

7shallowdampmoderatemoderate

7deepdamphighmoderate

Nutrients nitrates phosphates sulfates potassium


————

poorpoormoderatemoderate


goodgoodgoodmoderate

Rate

of r

eact

ion

0

sunrise noon sunset sunrise

photosynthesis

respiration

Figure E1.7 Rates of reaction in a pond

13 The graph shown in Figure E1.7 compares the rates of photosynthesis and respiration in a pond on a sunny day. Water plants and one species of freshwater fish live in the pond.

(a) Explain why the rate of photosynthesis drops to zero at night, but the rate of respiration remains fairly constant.

(b) Estimate the times at which the most and least amounts of dissolved oxygen would be found in the pond.

(c) More fish were added to the pond. A short time later, the same number of fish died. Moreover, the fish died just before sunrise. Explain how this could be related to the rates of photosynthesis and respiration in the pond.

Documents

Biology In Context Module 1