Advanced Higher Biology

UNIT 2Environmental

Biology

Introduction to EcologyThe study of ecology is a scientific discipline thatattempts to understand the interactions betweenorganisms and their environment. This Unit considers the biological processes that result in the flow of energy and circulation of materials in ecosystems.Emphasis is placed on the process of decompositionbecause of its key role in recycling materials.The interactions within ecosystems are studied by consideration of the abiotic and biotic factors that affect ecosystems. We will also look at the consequences of such interactions as well as human impact on the environment.

(a) CIRCULATION IN ECOSYSTEMS

1. Energy 1. Energy (Energy fixation & Energy flow)(Energy fixation & Energy flow)

2. Circulation of 2. Circulation of nutrients nutrients (Decomposition, (Decomposition, Nutrient Cycling – N & Nutrient Cycling – N & Ph Cycles)Ph Cycles)

Energy Fixation• Photosynthesis is fundamental to

energy flow through an ecosystem. It is achieved by the autotrophic organisms that convert the energy of sunlight into chemical energy. Energy fixation is achieved by photosynthesis.

• All organisms require energy to carry out cellular activity, growth and reproduction. They obtain that energy from the food they eat.

NutritionAUTOTROPHSThe term autotrophic ('self-feeding') defines organisms which are able to use external sources of energy in the synthesis of their organic food materials.

PHOTOAUTOTROPHS : use light energy, via photosynthesis, to make their organic molecules

CHEMOAUTOTROPHS : use energy from breakdown of inorganic molecules to synthesis complex organic molecules

HETEROTROPHS

Heterotrophic ('other-feeding') organisms obtain their energy by breaking down substances obtained from the bodies of other organisms.

HERBIVORES [= HERBIVORES [= Primary Consumers]Primary Consumers]: feed only on green plants

CARNIVORES CARNIVORES [Secondary/tertiary [Secondary/tertiary Consumers]Consumers]: feed only on other animals

OMNIVORESOMNIVORES: feed on both plants and animals

SAPROTROPHS Saprotropic (‘decay-feeding’) organisms obtain

their nutrients from non-living organic matter,

usually dead and decaying plant or animal matter,

by absorbing soluble organic compounds. Since

saprotrophs cannot make food for themselves,

they are considered a type of heterotroph.heterotroph. They

include most fungi (the rest being parasites);

many bacteria and protozoa; animals such as

dung beetles and vultures; and a few unusual

plants, including several orchids.

Productivity

• PRIMARY PRODUCTIVITY: The amount of light energy converted into chemical energy by autotrophs in an ecosystem during a given period of time. Measured by the rate of accumulation of BIOMASS BIOMASS

(dry weight of vegetation)(dry weight of vegetation) in the ecosystem [usually expressed as per unit area in a given time e.g. g/m2/yr]

• GROSS PRIMARY PRODUCTIVITY (GPP): the total primary productivity

HOWEVER:HOWEVER: Remember that plants not only photosynthesise, they also respire. Therefore not all the material produced is stored (and available as food for the primary consumers). Some of it is used for cellular respiration and other metabolic activities by the plant itself.

Net Primary Productivity

• The energy available to the next level in a food chain or food web is the gross primary productivity (GPP) minus the energy used by the plant during respiration (R) and is called the NET PRIMARY PRODUCTIVITY (NPP)

• This can be written as an equation: This can be written as an equation: NPP = GPP - RNPP = GPP - R

• Net primary productivity (NPP) is of interest because it represents the chemical energy available to the primary consumers (herbivores) and is the beginning of the flow of energy through an ecosystem.

Factors affecting productivity

• The same as those affecting photosynthesis!– Light Intensity– Temperature– Rainfall– Soil Water/Nutrients

– CO2 concentration

Energy Flow

• Energy fixation and productivity are the basis of ecosystem productivity. In this section the aim is to discuss how that energy flows through an ecosystem, and to consider the efficiency of that energy flow.

Ecological Niches

• There are three basic niches (or feeding relationships) in the flow of energy through an ecosystem: producers (autotrophs), consumers (heterotrophs) and decomposers (saprotrophs).

Energy in an Ecosystem FLOWS from the SUN to Autotrophs (Producers) then to Heterotrophs (Herbivores) that eat the Autotrophs, then to Heterotrophs (Carnivores) that feed on other organisms.

Trophic Levels• Feeding relationships and therefore the flow of energy

can be represented as a food chain. Each link in the chain is called a trophic level (‘trophic’ meaning ‘feeding’)

• Each trophic level is the same number of steps from the Sun:

- ProducersProducers (Autotrophs) are the 1st Trophic Level

- HerbivoresHerbivores are the 2nd Trophic Level

- CarnivoresCarnivores are the 3rd/4th/5th Trophic Levels

• Most Animals (carnivores) feed at more than one Trophic Level

• In most ecosystems the feeding relationships (and the transfer of energy) are represented more accurately by a food web

Food Web

Energy Transfer & Efficiency

• The leaves only use some of the light energy which shines on them for photosynthesis.

• The rest is …

Consider this simple food chain:

REFLECTEDREFLECTED off the leaves

TRANSMITTEDTRANSMITTED through the leaves or

belongs to WAVELENGTHSWAVELENGTHS that cannot be used.

Energy Transfer & Loss• BUT, only about 1%1% of the light energy striking a plant

is converted into net primary productivitynet primary productivity and available to be eaten by the caterpillars.

• Only a proportion of this energy (that contained in the leaves and shoots) is consumed by the caterpillars, where most of it is used in respirationrespiration and heatheat production, and some is egested as wastewaste.

• Only a small fraction (about 10%10%) is used for growthgrowth and available to the next trophic level, the sparrow.

• Similarly only about 10%10% of the energy the sparrow receives from the caterpillars is available to be passed on to the next trophic level (the eagle)

Ecological Efficiency• The ecological efficiencyecological efficiency is the ratio of net productivity (ie

the amount of energy) at one trophic level to net productivity at the level below

NPP (trophic level x) : NPP (trophic level x -1)

• Ecological efficiencies vary depending on the organisms involved but usually range from 5-20%.5-20%.

• This means that 80-95%80-95% of the energy at one level never transfers to the next.

• Because energy diminishes at each successive trophic level, food webs rarely contain more than 4 or 5 trophic levels.

This is the reason why, generally speaking, the biomass of and the number

of organisms in each trophic level decrease as you move along a food chain

Pyramids of numbers, biomass and productivity

• In an ecosystem, productivity, biomass and numbers of organisms tend to DECREASEDECREASE at each trophic level in a food web.

• This information can be quantified and illustrated diagramatically as ecological pyramids

Pyramids of Number• Numbers of organisms in a given

area in a given time are counted and then grouped into trophic levels.

• Pyramids of numbers typically show a broad base of producers and a successive decrease in number of animals at each level

• There are several situations that show inverted pyramids of numbers. For example, a tree, as the primary producer, supports large numbers of insects, which in turn are the food source of large numbers of birds or other predators

Pyramids of Biomass• Each block = total dry mass of

organisms at that trophic level.

• At each level the biomass

decreasesdecreases. Normally a pyramid of biomass would have a broad base, getting narrower at each succeeding level.

Occasionally, however, inverted pyramids of biomass can be found where the primary consumers outweigh the primary producers. E.g. In aquatic ecosystems the primary producers are algae. They are very productive and have a high turnover rate. This means that they grow in numbers rapidly but are also eaten in large numbers by zooplankton and small fish. Thus at any given time the biomass of the producers will be less than that of the primary consumers.

Pyramid of Productivity• Size of each block is proportional to the productivityproductivity of

(or energy available at) each level.

• The producers form the foundation of the pyramid

Qu: Look at the inverted pyramid of mass found in a marine phytoplankton food chain. Would the pyramid of productivity for this food chain be inverted or upright?

Pyramid of Productivity• Size of each block is proportional to the productivityproductivity of

(or energy available at) each level.

• The producers form the foundation of the pyramid

Qu: Look at the inverted pyramid of mass found in a marine phytoplankton food chain. Would the pyramid of productivity for this food chain be inverted or upright?

Circulation of Nutrients• Despite an inexhaustible influx of energy in the

form of sunlight, continuation of life depends on recycling of essential chemical elements. These elements are continually cycled between the environment and living organisms as nutrients

are absorbed and wastes released. • The cyclingcycling of nutrients from the

decompositiondecomposition of dead or decaying matterdead or decaying matter, provides essential elements required for metabolic processes, such as photosynthesis, and constructing fundamental organic molecules, such as amino acids and nucleic acids.

The role of soil in decomposition

• Soil consists of 2 main components…

– INORGANICINORGANIC

– ORGANIC ORGANIC

• OxygenOxygen and moisturemoisture, trapped in the spaces (pores) between the soil particles, are required by micro-organisms to decompose materials.

Dead/Decaying organisms, parts of organisms, faeces and urine

derived from weathering of rocks. Type determined by relative proportions of SAND, SILT and CLAY particlesvery important agriculturally.

The structure of soil • The structure of soil is vital to nutrient recycling

in terrestrial ecosystems

Organic litter : plant/animal debris

Topsoil containing humus : roots, invertebrates, micro-organisms

Leaching of nutrients from the soil

Subsoil : rich in minerals & organic material, some roots

Weathered rock : sand, gravel, clay

Impermeable Bedrock

Soil fauna• Wide variety including…

– FUNGIFUNGI– BACTERIABACTERIA - - [Insert Soil micro-organisms

table]

– INVERTEBRATESINVERTEBRATES - - worms, woodlice, spiders, nematodes, larvae

• Essential to soil productivity - directly affect quality of soil

Rhizosphere• The area where plant rootsplant roots and soilsoil come

into contact.

• There are large numbers of micro-micro-organismsorganisms here that differ in species composition.

• The major micro-organisms found are the bacteria whose growth is stimulated by various nutrients released by the plant roots. In exchange, the by-products of microbial metabolism that are released into the soil stimulate plant growth.

Decomposers and Detritivores

• These organisms feed on waste or dead organic matterwaste or dead organic matter such as dead leaves, dead bodies, or waste products, decomposing it by producing enzymes to break it down. Action of detritivores increases the activity of decomposers:-

DETRITIVORES :DETRITIVORES :• Detritus eating soil

invertebrates e.g. Earthworms, woodlice, spiders and nematodes.

• Physically reduce detritus particle sizes to produce humus [FRAGMENTATIONFRAGMENTATION= Larger surface area for decomposers to work on!]

• Enhance fertility of the soil by incorporating leaf surface litter into the soil

• PHYSICAL DECOMPOSITIONPHYSICAL DECOMPOSITION

DECOMPOSERS :DECOMPOSERS :• Fungi & Bacteria • Use waste materials as

energy, carbon & nutrient sources

• Carry out respiration to release CO2

• Chemically breakdown [using ENZYMESENZYMES] detritus (decaying matter) to release inorganic ions (mineralisation)

• CHEMICAL DECOMPOSITIONCHEMICAL DECOMPOSITION

Detritus Food Chain

• A food chain based on dead dead organic materialorganic material

• A food chain containing a primary producer which is a soil soil invertebrateinvertebrate e.g. Earthworm.

• A Detritus food chain is essential to the energy flow of an ecosystem.

Decomposition• The breakdown of dead organic

matter(involving both physical and biological processes) with the release of inorganic nutrients into the soil.

• These nutrients are then available for uptake by plants and other primary producers– Undecomposed material = LITTER LITTER

[DETRITUS][DETRITUS]

– Completely decomposed matter = HUMUSHUMUS

Humus• Completely decomposed material• Dark brown in colour• Composition varies depending on which

organic molecules are present

• Improves aeration, water and nutrient retention; and so soil structure

Humus content = soil fertility

Mineralisation

• Occurs at the same time as humus is being formed

• Process which changes essential mineralsessential minerals e.g. N, P and S from – Organic Organic Inorganic compounds Inorganic compounds e.g.

ammonium, orthophosphate and sulphate

• Results in nutrients and minerals being released from dead organisms into a food chain

Rate Of Decomposition

• This varies within different biomes and is dependent on several factors:

– Type of organic matter– Number and types of decomposers

and detritivores– Environmental conditions i.e.

temp, moisture etc

The Carbon Cycle

Carbon is removedremoved from the atmosphere by fixation during photosynthesis and returnedreturned by respiration, decomposition & burning

fossil fuels

The Nitrogen Cycle1)1) FIXATIONFIXATION : the reduction of atmospheric nitrogen to

ammonia by CYANOBACTERIACYANOBACTERIA. Rhizobium fix nitrogen in the root nodules of legumes. Catalysed by enzyme complex NITROGENASE. LEGHAEMOGLOBIN is a molecule made by both the plant and the bacteria which limits the amount of O2 reaching the bacteria. This is important as nitrogen-fixing is an anaerobic process

2)2) NITRIFICATIONNITRIFICATION : the conversion of ammonium to nitrite to nitrates by NITROSOMONAS and NITROBACTER. Nitrates and ammonium are assimilated by plants into proteins and amino acids. They are lost by leaching and denitrifying bacteria. Aerobic process.

3)3) DENITRIFICATIONDENITRIFICATION : returns nitrogen to the atmosphere

4)4) AMMONIFICATIONAMMONIFICATION : the decomposition of organic nitrogen to ammonia

Water saturation of the soil affects the cycling of nitrogen.

i.e. H20 = O2 anaerobic/aerobic affect different stages of cycle

The Nitrogen Cycle

The Phosphorus Cycle• Phosphorus is a major element

of ATP, Nucleic Acids, Phospholipids

1) PHOSPHATEPHOSPHATE added to the soil by the weathering of rocks

2) Taken up by primary producers incorparated into molecules

3) PHOSPHORUSPHOSPHORUS is taken up by consumers

4) PHOSPHORUSPHOSPHORUS returned to the soil by decomposition (faeces/detritus)

• Phosphate is a limiting factor in the productivity of aquatic ecosystems as it has LOW SOLUBILITY (needed by ALGAE!)

• Phosphate enrichment can lead to eutrophication (as can excess Nitrogen)

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(b) INTERACTIONS IN ECOSYSTEMS

1. Biotic Interactions 1. Biotic Interactions (Predation, Grazing, Competition) (Predation, Grazing, Competition)

2. Symbiotic Relationships2. Symbiotic Relationships (Parasitism, Commensalism, Mutualism) (Parasitism, Commensalism, Mutualism)

3.3. Costs,Benefits & Costs,Benefits & Consequences Consequences of these of these interactionsinteractions (Interactions between species, Interactions with (Interactions between species, Interactions with the environment)the environment)

Biotic Interactions

• This is the interaction between living things living things

–Predator/prey relationships –Plant/herbivore relationships–Competition –Symbiosis

Abiotic Interactions• These are interactions that exist

between the organismsorganisms and the environmentenvironment :

- Temperature - Light - Pressure - Salinity - Water availability - pH - Nutrients - Exposure to wind or waves

Density Independent Factors

• These are factors which reduce the population numbers independently of the population density

The proportion that dies could be the same whether the population is dense or not

- Forest Fire - Floods - Volcanic eruptions - Prolonged drought - Acid rain

Density Dependent Factors

• These are all biotic interactions• These cause the population to

decrease when the population is high and increase when the population is low

- Predation - Competition - Disease

Inter-specific and Intra-specific Interactions

• These interactions are always involved in competition

INTERINTER is competition between species e.g. GRAZING, PREDATION AND PARASITISM

INTRAINTRA is competition within the speciese.g. TERRITORIAL BEHAVIOUR, DOMINANCE, MATING, RESOURCES

Predation• In a predator/prey relationship both

the species can benefit • Predators obtains food • Reduced numbers in prey means more

resources for those individuals that are left

• Both the predator and prey population is governed by one another, however the exact nature of this can differ

Predator-Prey Relationship

The pattern between the two can be groupedinto 4 types:

1) Stable coexistence: where both populations remain stable 2) Cyclical variations: regular increases and decreases occur in the populations3) Erratic swings: large scale “blooms” can take place at an irregular time, due to unstable populations of prey or predator, where a small change in the environment can have a major effect on the animal.4) Extinction : due to over hunting of prey

Predator-Prey Relationship

One of these 4 patterns will occur depending on a variety of factors:

– The CARRYING CAPACITYCARRYING CAPACITY of the habitat (the maximum number of individuals that can be supported by a particular ecosystem on a long term basis)

– The PREY REPRODUCTION RATEPREY REPRODUCTION RATE

– The PREDATOR REPRODUCTION RATEPREDATOR REPRODUCTION RATE – The degree of FLEXIBILITYFLEXIBILITY of the predator

in it’s ability to respond to changes in the prey population

Flexibility of the Predator

• If the prey increased, the predator would naturally eat more, but this only happens if the predator is not eating it’s maximum number of prey

• If the increase in prey is long term, then there will be an increase in the predator offspring that survive from reproduction as there is more food available and therefore less competition for food

• If the prey population becomes very large there are two possible fates of interaction:

• STABLE COEXISTENCESTABLE COEXISTENCE : – Predators prevent prey from

exceeding the carrying capacity– To do this predators must reproduce

quickly compared to prey and to eat more when there are more prey

• CYCLICAL VARIATIONSCYCLICAL VARIATIONS : – Here the predators are less responsive

to fluctuations, due to slow reproductive rate or have reached a maximum level of feeding

Cycling• Cycling results due to time lags,

which are the responses of the predator to the change in population numbers of the prey.

• The prey increases, then in some time the predator population increases

• As the predator population rises their prey population begins fall

• The lack of food reduces predator number …………… and so on!

Case Study: Snowshoe Hare and the Canadian

Lynx• The information on the populations

of both animals appears to give the perfect predator/prey relationship in a cycling effect

• However, there are many other factors to consider, proving only that an ecosystem is a complicated network of interactions

Predator/Prey Cycle

The Role of Predators in Maintaining Diversity

in Ecosystems• When different species are competing for the

same resources, one will succeed at the expense of another

• The weaker species will be lost from the habitat [COMPETITIVE EXCLUSION][COMPETITIVE EXCLUSION]

• If, however, predation reduces the numbers of strong competing species, the weaker species have more of a survival chancesurvival chance

• This increases the DIVERSITY OF THE ECOSYSTEMDIVERSITY OF THE ECOSYSTEM. The more diverse an ecosystem the more stable it becomes, i.e. tends towards a climax community

Defences against predation

• During the process of evolution, predators have evolved ways to make them more successful at catching their prey (e.g. claws, fangs, poisons).

• Similarly, prey organisms have evolved adaptations to help them avoid being caughtcaught or eateneaten by predators

Prey Defences

•3 main adaptations:

• CamoflageCamoflage- Crypsis- Disruptive colouration

• Warning Warning ColourationColouration• MimicryMimicry

Camoflage• An adaptation in form, pattern,

colour or behaviour which enables the animal to escape detection by predators by blending in with it’s surroundings

• Two interrelated but logically distinct mechanisms for this are:– CRYPSIS CRYPSIS : : the ability of an organism to ‘blend

in’ with it’s environment – DISRUPTIVE COLOURATIONDISRUPTIVE COLOURATION: allows an otherwise

visible organism to remain indiscernible from the surrounding environment by ‘breaking up’ it’s outline

Cryptic Colouration

• Blend into the background !

• The animal's colours are a random sample of the backgroundExamples: peppered moths, peppered moths, chameleonschameleons

Disruptive Coloration• Disruptive patterns

(spots/stripes/markings) break up an animal's outline

• Forming a pattern that does not coincide with the contour and outline of the body makes it difficult for other animals to see it!

Warning or Aposematic Coloration

• This is a form of coloration which discourages a predator from eating an organism

• There is often a sting, poison, or painful bite associated to it.

• Animals learn these colours by trial and error

• Red, black and yellow are common colours and are called aposematic colours (meaning ‘away signal’)

• Many individual share the same pattern [convergent evolutionconvergent evolution]

• This prevents young from having to try many combinations to learn all of the animals not to eat

• This convergent evolution is a form of mimicry

Batesian mimicry• Involves a palatable, unprotected

species (the mimic) that closely resembles a dangerous, poisonous or protected species (the model) and therefore is similarly avoided by predators

The scarlet king snake on the left is the mimic, and the coral snake on the right is the poisonous one

SCARLET KING SNAKESCARLET KING SNAKE CORAL SNAKECORAL SNAKE

"Red on yellow, kill a fellow. Red on black, won't hurt Jack."

Mullerian mimicry• Involves two unpalatable species

that are mimics of each other with conspicuous warning coloration (aposematic coloration)

Grazing• Grazing is a form of INTERSPECIFIC INTERACTIONINTERSPECIFIC INTERACTION

• A ‘GRAZER’‘GRAZER’ = any species that moves from one ‘victim’ to another feeding on part of it without actually killing it outright e.g. grasshoppers that jump from plant to plant, chewing a portion of the leaves as they go

• Grazers, like predators, can both INCREASEINCREASE or DECREASEDECREASE species diversity depending on the intensity of the feeding of the grazers and on the type of plant being grazed

• As an ecosystem tends toward a climax community, the process can be stopped or diverted away from the natural succession

• This can be unnatural by implementing agriculture OR naturally by grazing animals

• Grazing animals favour grasses as these species are more vigorous competitors due to low growing points

• Shrubs have meristems at the tips of shoots, which are easily eaten by grazers

Apical and Basal Meristems

• Meristem = point of growth in a plant

• Grasses have BASAL MERISTEMSBASAL MERISTEMS (growing points under the soil)

• Shrubs have APICAL MERISTEMSAPICAL MERISTEMS (growing points at the tips of shoots), which are easily eaten by grazers

Overgrazing• When overgrazing occurs, this prevents

the build up of leaf litter • Leaf litter is important in starting bush

fires by lightning. Bush fires remove the shrubs from the ecosystem, but grasses thrive as they have basal meristems

• Therefore if an grassland is overgrazed, shrubs will become more dominant, thus again reducing diversity

• Many shrubs are not palatable to grazers, therefore they move away from the habitat

Grassland Habitats• These habitats provide an area of land

which has a huge diversity of organisms living in it

• If you remove a grazing animal, e.g. rabbits in Britain, the whole diversity soon disappears as the area becomes a wooded community

• Woods lack diversity of plants, which in turn effects animal diversity, thus species can be lost from the ecosystem

• Woodland areas have a different soil type which is permanently changed after a wood has been there

Competition• Competition is where 2 or more organisms need

the same resource, and the resource is limited • This does not always result in fighting or

confrontation !• Where there is competition, one or both of the

organisms will lack the resource • When the resource is required by different

species, and there is a lack of the resource, then the two organism’s niche overlaps

• If the resource is unlimited then the overlapping of their niche is not a problem. The GREATERGREATER the overlap in the niche the MORE CHANCEMORE CHANCE there is for competition

Interspecific vs Intraspecific competition

• INTERSPECIFICINTERSPECIFIC competition is competition between organisms of two different species

• INTRASPECIFICINTRASPECIFIC competition is competition between organisms of the same species

• Interspecific competition is not as intense as intraspecific competition, due to organisms of the same species having the greatest overlap in niches

Exploitation and Interference Competition

• All competitions between organisms can be grouped as EXPLOITATIONEXPLOITATION or INTERFERENCEINTERFERENCE competition

• EXPLOITATIONEXPLOITATION is when all individuals have the equal access to the resource, but they differ in how fast or how efficiently they can exploit it

• INTERFERENCEINTERFERENCE is when certain individuals are able to restrict or prevent access of others to the resource and so control the use of it

Exploitation Competition

• There are two possible outcomes from this competition: – They will co-existco-exist – One of the two will be excludedexcluded

• In theory, if there is enough overlap in their requirements, one species will always have a slight advantage and will succeed at the expense of the other

Gause’s experiment with Paramecium

The two species of Paramecium used by Gause grew well by themselves but P. caudium was out competed by P. aurelia when the two were grown together

Interference Competition

• In this case on organism will often show AGGRESSIONAGGRESSION to prevent another organism sharing a resource, e.g. territorial behaviour of the robin. The territory contains just enough resources for the breeding pair

• In plants, this can be seen in the ability for some to GROW QUICKLYGROW QUICKLY and block the sunlight out for others e.g. by growing in a lateral manner

Fundamental Niche and Realised Niche

• The FUNDAMENTAL NICHEFUNDAMENTAL NICHE is the theoretical niche containing all of the required resources for an idealistic life

• This cannot exist as there a huge network of interactions with other species, and each species will try and exploit the resources

• The actual resources which a population uses are its REALISED NICHEREALISED NICHE

Case Study of Barnacle populations

Semibalanus balanoides Habitat – low tide mark to the lowest high tide mark as they have little toleration to desiccation

Chthamalus stellatus Habitat – found in areas of rocks which may be exposed to air for long periods, as they can survive some period of desiccation

East Coast of Scotland

West Coast of Scotland

Resource Partitioning

• Species that share the same habitat and have similar needs frequently use resources in somewhat different ways - so that they do not come into direct competition for at least part of the limiting resource

• This is called RESOURCE PARTITIONINGRESOURCE PARTITIONING

The Competitive Exclusion Principle

Early in the twentieth century, two mathematical biologists, A.J.Lotka and V. Volterra developed a model of population growth to predict the outcome of competition

Their models suggest that two species cannot compete for the same limiting resource for long. Even a minute reproductive advantage leads to the replacement of one species by the other

The Damaging Effects of Exotic Species

• The Rhododendron ponticum is a shrub which was introduced to Scotland

• It is successful competitor in acidic soils, many soils in the Scottish Highlands are acidic

• It creates a dense canopy of leaves, which shades smaller shrubs, and therefore is a good INTERFERINGINTERFERING competitor

• In its native habitat it has grazers as they have evolved together, however in Scotland the sheep and rabbits do not eat it

These invasive, non-native species are a major threat to the environment because they ... can change an entire habitat, placing ecosystems

at risk crowd out or replace native species that are

beneficial to a habitat damage human enterprise, such as fisheries,

costing the economy millions of dollars Other examples:

• The zebra mussel, accidentally brought to the United States from southern Russia, transforms aquatic habitats by filtering prodigious amounts of water (thereby lowering densities of planktonic organisms) and settling in dense masses over vast areas. At least thirty freshwater mussel species are threatened with extinction by the zebra mussel

[HANDOUT / RESEARCH][HANDOUT / RESEARCH]

The Importance of Survival for Weak

Competitors• Species diversitySpecies diversity is important to all ecosystems • The diversity provides flexibility when the

environment changes • Therefore competitors change when the

environment changes • A less competitive species survives as they can

adapt its niche slightly, and therefore maintain a presence

• They are a valuable reserve for an alternative ecosystem. Without an alternative, if the environment were to change then the stability of the environment would be in jeopardy

Symbiotic RelationshipsSymbiotic Relationships

-- ParasitismParasitism

-- CommensalismCommensalism

-- MutualismMutualism

SYMBIOSISSYMBIOSIS refers to relationships between organisms of DIFFERENTDIFFERENT species that show an intimate association with each otherSymbiotic relationships provide at least ONEONE of the participating species with a nutritional advantage3 types of symbiosis have been recognised depending on the nature of the relationship:

Parasitism• Interaction in which one

organism, the parasite, derives nourishment from the other organism, the host

• Parasites are therefore chemoautotrophs

• This relationship is detrimental to the host, however a true parasite does normally not kill its host

Obligate vs Facultative• Most parasites are OBLIGATEOBLIGATE - that is they must

live parasitically and die when their host dies

• Obligate parasites also have very few specialised structures for feeding or locomotion

• Some fungi are FACULTATIVEFACULTATIVE parasites since they can continue to feed saprophytically once their host has died

• Fewer facultative parasites have evolved as they must form complicated systems to detect, take in and digest food. Due to natural selection they would be at a disadvantage to obligate parasites.

Parasite TypesECTOPARASITESECTOPARASITES - remain external to

the hoste.g. ticks, fleas, leeches

ENDOPARASITESENDOPARASITES

- live inside the body of the host

e.g. liver flukes, tapeworms, malarial parasites

MICROPARASITESMICROPARASITES

• They are small and have a short generation time e.g. viruses, bacteria and protozoans [Plasmodium spp]

• The duration of infection is short compared to the life span of the host

MACROPARASITESMACROPARASITES

• Longer generation time and tendency to persist causing continual reinfection e.g. roundworms tapeworms and fungi

• Intermediate hosts more common

Parasite Transmission• Many parasites complete their entire lifecycle on or

in a single host organism• However, many alternate between 2 or more host

species, specialising on a different host species at each stage in their lifecycle

• 2 general types of transmission:– VERTICALVERTICAL: from mother offspring e.g. HIV– HORIZONTALHORIZONTAL: between members of a population

• Direct Contact e.g. Headlice• Resistant Stages e.g. Liver fluke• Secondary host species / Vectors e.g. Mosquitoes

Parasite Transmission Case Study: MALARIACase Study: MALARIA

• Malaria is a mosquito-borne disease caused by a parasite Plasmodium falciparum, P. vivax, P. ovale and P. malariae

• People with malaria often experience fever, chills, and flu-like illness

• Left untreated, they may develop severe complications and die

• Almost 85% of the world's malaria occurs in sub-Saharan Africa

• Each year 350-500 million cases of malaria occur worldwide, and over one million people die, most of them young children in sub-Saharan Africa

Humans are the INTERMEDIATE HOST and RESERVOIR of the parasite, and the mosquito is the DEFINITIVE HOST and VECTOR.

Female anopheline mosquitoes become infected only if they take a blood meal from a person whose blood contains mature male and female stages of the parasite.

A cycle of development and multiplication then begins with union of the male and female gametocytes in the stomach of the mosquito and ends with parasites, called sporozoites, in its salivary glands, which are infective to humans.

The time required for the complete maturation of the parasite in the mosquito varies and depends on the Plasmodium species and external

temperature.

Lifecycle of Malaria Parasite

1

2

3

The gametocytes are ingested by the female mosquito in a bloodmeal from an infected human.

The gametocytes fuse to produce a zygote.The zygote secrete a cyst containing sporozoites

formed from meiotic divisions

Sporozites enters the liver cell and during the next two weeks the intracellular parasite reproduces by mitosis

within a liver cell to form as many as 200,000 merozoites!

On maturation, the merozoites rupture the liver cells and are are released into the blood where they invade human

red blood cells

In the red blood cells, the parasite matures asexually to produce another 10-20 merozoites which in turn can rupture the red blood cell and invade more liver

cells or red blood cells

[Animation]

Evolution of Host/Parasite relationship

• Most parasitic relationships are very specific and complex

• The parasite and the host have co-evolved

• This means that the host has developed a defence mechanism e.g. immune system or hydrochloric acid in the stomach, to prevent the parasite from causing any harm if it has entered the body.

• The longer the relationship has existed, the more host specific the parasite becomes

Modification of Parasites

STRUCTURALSTRUCTURAL- Absence/degeneration

of feeding and locomotory organs

- Highly specialised mouth parts as in fluid feeders e.g. aphids

- Boring devices to aid entry into host

- Attachment organs e.g. hooks or suckers

- Resistant outer covering

- Degeneracy of sense organs associated with the constancy of the parasites environment

PHYSIOLOGICALPHYSIOLOGICAL- Exoenzyme production

to digest host tissue external to parasite

- Anticoagulants

- Chemosensitivty to reach optimum location in hosts body

- Production of anti-enzymes

- Ability to respire in anaerobic conditions

REPRODUCTIVEREPRODUCTIVE- Hermaphrodites

- Enormous numbers of reproductive bodies cysts and spores

- Resistant reproduction bodies when external to the host

- Use of secondary hosts as vectors

Host Responses to Parasite Infection

• Organisms respond to parasites in different ways:– Vertebrate hosts infected with microparasites mount an

immunological response

– Vertebrate hosts infected with ectoparasites have other behavioural strategies e.g.

• Preening or grooming each other to remove ectoparasites e.g. chimpanzees. • Move away from the infected area e.g. caribou move to higher altitudes during

the summer months when the mosquito population is particularly dense to avoid attacks

– Plants respond to parasitic infection in several ways:

• e.g. in tobacco plants, if just one leaf is infected with the tobacco mosaic virus, there is an increase in the defensive chemicals throughout the plant-protects the plant from a variety of parasites and from the effects of grazing by herbivores. In addition, the plant will often kill the cells in the area that has been infected by the parasite, causing localised cell death. This deprives the parasite of its source of food and prevents parasitic spread to other cells.

Some particularly Some particularly nasty parasites ...nasty parasites ...

Cymothoa exigua

Biting Your Tongue, So You Don’t Have To!

Leucochloridium paradoxum

A parasite for sore eyes!

Sacculina carcini: Reasons You Shouldn’t

Pick up a Hitchhiker

Screw

worms: Causing Trouble Right out of the Hatch

Koch’s Postulates• There may be several different organisms growing in an infected

sample, although most will have appeared after the initial disease has weakened the host.

• Koch's postulates need to be satisfied in order to identify the organism that is causing a disease

• Koch was one of the original researchers into tuberculosis, in the 19th century. In an attempt to define what an infectious disease actually is, he formulated his famous postulates, which now bears his name. Basically if,

1. An organism can be isolated from a host suffering from the disease ANDAND

2. The organism can be cultured in the laboratory ANDAND

3. The organism causes the same disease when introduced into another hostANDAND

4. The organism can be re-isolated from that host THENTHEN

The organism is the cause of the disease and the disease is an infectious disease

Commensalism• An interaction between species where

neither species is dependent on the other for its existence, but in this case only ONEONE of the partners benefits from the association

• In the strictest truth very few of these relationships exist, as it is very unlikely the two organisms can live together without them affecting each other

• Most examples of commensalism relationships are feeding or protection

Commensalism : An Example

PORCELAIN ANEMONE CRABS PORCELAIN ANEMONE CRABS AND THEIR HOST ANEMONESAND THEIR HOST ANEMONES

- These crabs are primarily suspension-feeding animals, and they use their large basket-like feeding appendages to sweep the water to get their food

- They don't harm the anemones, but they benefit by gaining protection from their host. Few fish will hazard getting eaten by an anemone simply for the chance to snack on the crab

Mutualism• An interspecific

interaction that benefits BOTHBOTH species

• They exchange food or provide shelter or protection, but may still be able to live an independent lifeIn return for shelter, the clownfish cleans the anemones, chasing away their predators and dropping scraps of food for the anemone to eat

Mutualism: examples

There are many different examples of mutualistic relationships:

• Plants and microbes e.g. rhizobium in root nodules

• Protists and fungi e.g. lichen

• Terrestrial plants and insects, e.g. pollination

• Animals and protists/bacteria e.g. ruminants, corals

• Animals and other animals e.g. crocodile and plover bird

• All orchids depend on fungi called mycorrhizae at some point during their life cycle

• The fungi grow partly on the root and aid the plant in the uptake of nutrients

• The fungi benefit as they ingest some of the food from plant photosynthesis

• Most plants have to search through the soil with their roots to find nitrogen which is a critical nutrient required for growth

• Legumes, however, form symbiotic relationships with Rhizobium bacteria

• The Rhizobium live in little nodules in the roots of the legumes and fix atmospheric nitrogen into ammonium or nitrate, forms of nitrogen that can be used by the plant i.e. Rhizobium turn air into fertiliser!

                                                                        

•The plant benefits because it gains nitrogen. •The bacteria benefit because they get sugars and nutrients to survive

[ HANDOUT! ]

The Costs, Benefits and Consequences of

Interactions-- Interaction between species Interaction between species

-- Interactions with the environmentInteractions with the environment

We have studied various types of biotic interaction that exist between species in an

ecosystem. Now we are going to look at these interactions again, but this time we are going

to concentrate on the COSTS, BENEFITS and CONSEQUENCES that these interactions have to

the different species

Interactions between species: SUMMARYSUMMARY

Type of I nteraction Overall Eff ect on Population Density

Competition -/ -

Predation +/ -

Parasitism +/ -

Commensalism +/ 0

Mutualism +/ +

Effects of Host Health and Environmental

Factors• In most symbiotic relationships, a STABLESTABLE

relationship exists between the two species involved

• This is perhaps most important in parasitic relationships where it is necessary that the host, although affected in a negative way by the relationship, nevertheless remains healthy enough to be able to tolerate the parasite without being affected too seriously. If it is, it may die, which would be detrimental both to the host and to the parasite

• However, this stable balance in a parasite/host relationship can be changed by either:– Health and development of the host (BIOTICBIOTIC factor)

or

– Environmental conditions (ABIOTICABIOTIC factors)

• These factors are crucial in altering the balance of an ecosystem

• In general if the health of the organism is good then it will hardly feel the effects of some of the environmental factors such as cold and wet conditions

• However if an organism is weak, then these factors will be detrimental e.g. HIV infection, overcrowding in seedlings, Botyritis infection in raspberries

Examples• People who are HIV positive and whose immune system is

therefore compromised, tend to be more at risk from opportunistic infections like pneumonia and tuberculosis than individuals whose immune system is healthy

• Seedlings which are grown in overcrowded conditions tend to grow spindly and weak and are more at risk of infections (which can pass more quickly from one individual to another in overcrowded conditions) than ones given more space. This is why gardeners 'thin' their crops of seedling plants, so that those which remain will have a better chance of growing into healthy adult plants, producing more, larger blooms etc.

• Soft fruits such as raspberries are prone to a parasitic fungal infection called Botrytis. However, how badly the fruit is affected by the parasite is dependent in part by how humid the environment is

The management of symbiotic relationships

• THEREFORE, host health and environmental conditions, such as overcrowding and humidity, can alter the balance of host/parasite interactions

• Humans can MANAGEMANAGE these factors to change the balance in favour of the host species in a variety of ways:

– by improving the quality of the host environment (e.g. reducing overcrowding) and

– by using DRUGSDRUGS, PESTICIDESPESTICIDES and HERBICIDESHERBICIDES.

Drugs

• An example of the use of drugs to alter the balance in the hosts favour is the use of anti-fungal ointment and powder in the treatment of athlete's foot - a common fungal infection in humans

• Also many farmers regularly include antibiotics in their animals' feed to prevent infection and so speed up the rate of growth of the animals. This activity is controversial, however, as it may be partly responsible for the evolution of antibiotic resistant bacteria

Pesticides

• Pesticides are chemicals used by farmers to kill insects and other animals which feed on or otherwise adversely affect crops and reduce the size of the crop yield

Herbicides• Herbicides are chemicals used by farmers to kill

other plant species which compete with the crop plants for resources such as space, light and water

• Such competition again, would reduce the growth of the crop plants and therefore also reduce the yield

• In order to prevent the crop plants being harmed by herbicides, selective herbicides are use

• These target specific types of plant - there are some which affect broad-leaved plants while leaving narrow-leaved plants unaffected while others do the opposite

Interactions with the environment

The Change of the Natural WorldThe Change of the Natural World• An organisms interaction with its environment can

change very quickly: e.g. rain, wind, sunlight, cloud cover

• Or more slowly on a monthly basis: e.g. seasons

• Longer timescales – continental drift and other geological effects, ice ages etc.

• All organisms within their lifespan have evolved ways to adjust to these changes

• However, changes can cause stress to the organism, where the condition is outside of their normal physiological range

• Despite changes in their external environment, organisms must maintain a constant internal environment : HOMEOSTASISHOMEOSTASIS

• Therefore, organisms must adapt to maintain a constant internal environment, or become restricted within a very small habitat

• Organisms have evolved a variety of BEHAVIOURALBEHAVIOURAL and PHYSIOLOGICALPHYSIOLOGICAL mechanisms to enable them to maintain homeostasis and deal with these changes :

BEHAVIOURALBEHAVIOURAL PHYSIOLOGICALPHYSIOLOGICAL

AVOIDANCEAVOIDANCE REGULATION & ADAPTATIONREGULATION & ADAPTATION

TOLERANCE & RESISTANCETOLERANCE & RESISTANCE

Behavioural Responses - AVOIDANCE

• Changes in an organism's behaviourChanges in an organism's behaviour which can be observed and which help them to survive changes in their environment– desert mammals being nocturnal and living in underground

burrows during the day to escape the heat of the desert sun

– Hibernation or migration to avoid low temperatures in winter e.g. swallows, whales, wildebeest

– Deciduous trees lose leaves in the low light intensity periods

– Sheep huddle in cold conditions

– Some animals adjust themselves to a particular position e.g. bees use wings to cool the hive

All avoidance usually involves a considerable investment of energy from the individuals concerned, but is beneficial

in the long-term

Physiological Responses

• Changes in the way an organism's body Changes in the way an organism's body functionsfunctions to enable it to survive in changing circumstances

• Many of these responses enable an organism to show a certain tolerance to the changes in its environment

Examples: – The camel's body tissues are very tolerant to dehydration -

it can lose up to 30% of its body water and still survive. In humans a 10% water loss causes kidney failure

– We shiver, hairs stand up, go pale etc in response to cold

– Wilting in plants

– Growing a thick coat of fur

• Information on a physical response to an environmental change can be turned into a RESPONSERESPONSE CURVECURVE

• This allows you to identify the optimum conditions and the range in which the organism will survive

• Response curves vary with SPECIESSPECIES, , STAGE OF LIFESTAGE OF LIFE and HEALTHHEALTH of organism when exposed to the stress

• It also varies with the TYPETYPE and INTENSITYINTENSITY of the stressful situation

Response curve

Although organisms can tolerate a range of external environmental changes, they function most efficiently at certain optimum

environmental conditions. An organism's responses to a changing environmental factor can be studied in the laboratory and a tolerance,

or performance, curve can be produced

Adaptations in Plants • There are two types of plant that have

adapted to controlling water concentrations in different habitats – XEROPHYTESXEROPHYTES

– HYDROPHYTESHYDROPHYTES

• Xerophytes are adapted to habitats where transpiration rates are high. These could be hot dry habitats which lack soil water (desert) or exposed windy habitats (moorland)

• Hydrophytes are adapted to living in submerged or partly submerged conditions in aquatic habitats

XEROPHYTES

• Sunken stomatal pits• Succulent tissues

• Leaf reduced to spines

• Long roots

• Stem with rounded shape

• Reversed stomatal rhythm

• Thick, waxy cuticle

• Rolled leaves

• Hairs

HYDROPHYTES• Aquatic plants have a problem

of obtaining oxygen

• The hydrophyte overcomes this problem by having air filled cavities

• Oxygen formed in photosynthesis is held within these air spaces

• Reduction of xylem is a further adaptation

• Water provides support for the plant, therefore the use of xylem in support is not required

• Any xylem found is located in a central column for maximum flexibility

Homeostasis• Process of maintaining constant internal environment

• Maintains INTRAcellular and EXTRAcellular fluids at a relatively constant ionic and osmotic compositions despite fluctuations in external conditions

• Abiotic factors e.g. water, light, temp., soil nutrients etc largely determine what organisms live there, homeostasis has enabled organisms to inhabit a diverse range of environments and to exist within narrow physiochemical ranges

• When this external environment CHANGESCHANGES there are 2 basic patterns of response:– CONFORMATIONCONFORMATION : change in internal environment with the external

environment– REGULATION : REGULATION : maintenance of internal environment regardless of

changes in the external environment

Conformation• Where internal variables fluctuate DIRECTLYDIRECTLY with the

external environment• Survival depends on the cellular resistance to damage

Osmoconformers : Marine invertebrates, such as crabs, shrimp and jellyfish.They are isosmotic and their body fluids are isotonic with their environment (conc. of solutes in the extracellular fluids is equal to that of the surrounding seawater). Therefore, no osmotic gradient exists, so no water enters or leaves the body of the organism. Osmoconformers do not alter their internal solute concentration

Poikilotherms : Animals whose body temperature varies with the surrounding environment. These are usually ectotherms (cold-blooded) that absorb heat from the surrounding environment e.g. snakes, lizards and marine fish

Regulation• Where the internal variables are maintained at levels

DIFFERENTDIFFERENT from their environment. This requires significant ENERGY COSTENERGY COST

Osmoregulators : e.g. freshwater organisms, terrestrial animals, body fluids are not isotonic with the environment and so need to use energy to regulate their internal osmolarity by excreting excess water or taking in additional water.They use a variety of osmoregulatory mechanisms to do this.

In hypotonic environments : they GAIN water by osmosis

In hypertonic environments : they LOSE water by osmosis

Homeotherms : are animals that maintain a constant body temperature. These are usually endotherms (warm-blooded) that derive heat from metabolism e.g. mammals, insects, birds

Habitat occupation of conformers &

regulators• CONFORMERSCONFORMERS can only survive in habitats

which provide their particular environmental conditions, although they conserve energy by not regulating

• REGULATORSREGULATORS use a lot of energy to carry out their homeostatic activities. However, the huge advantage they have is that they can colonise a range of different habitats since they can maintain their internal environment - thus can exploit habitats which conformers cannot!

Dormancy• Period in the life of an organism

during which the metabolic activity is greatly reduced

• This allows the organism to survive:– Bad environmental conditionsBad environmental conditions

– Severe resource shortageSevere resource shortage

• It can also allow for dispersal or internal change

Predictive vs Consequential

• 2 types of dormancy exist:

– PREDICTIVEPREDICTIVE : occurs in advance of adverse conditions e.g. hibernation

– CONSEQUENTIALCONSEQUENTIAL : occurs in response to prevailing conditions e.g. seed dormancy due to draught

Dormancy forms• RESTING SPORESRESTING SPORES : found in a wide diversity of forms.

Temperature and draught resistant stages exist in bacteria, fungi, plants and lower animals

• HIBERNATIONHIBERNATION – a period of inactivity in mammals associated with animals physiological changes resulting in a lowering of metabolic rate to conserve energy during periods of environmental extremes e.g. polar bear, dormice

• AESTIVATIONAESTIVATION – a period of inactivity associated with hot, dry periods [usually summer] during which the organism remains in a state of torpor with reduced metabolic rate e.g. lung fish

• DIAPAUSEDIAPAUSE – a form of dormancy typically found at a specific stage in an insect life history and involving complete cessation of growth and development together with suspended metabolism. This is controlled by hormones

AESTIVATION : ExampleAESTIVATION : Example

• African and South American lungfish are capable of surviving seasonal desiccationseasonal desiccation of habitats by burrowing into mud and aestivating throughout the dry season

• Changes in physiology allow the lungfish to slow its metabolism to greater than 1/60th1/60th of the normal metabolic rate, and protein waste is converted from ammonia, to less-toxic urea, (normally, lungfish excrete nitrogenous waste as ammonia directly into the water)

(c) HUMAN IMPACT ON THE ENVIRONMENT

Changes to EcosystemsChanges to Ecosystems(Changes in complexity, Effects of Intensive (Changes in complexity, Effects of Intensive Food Production, Effects of Increased Food Production, Effects of Increased

Energy Energy Production, Pollution)Production, Pollution)

Changes in Ecosystem Complexity

• Communities are always changing, usually from simple to more complex in a process called ECOLOGICAL SUCCESSION

• Succession is not affected by seasons and is the relatively orderly and repeatable series of changes in the types of species which occupy a given area through time

• It often begins with unstable, immature communities (pioneering, opportunistic, r-strategists) and proceeds to more mature, stable communities dominated by K-strategists

Types of Succession

• ALLOGENIC SUCCESSION:ALLOGENIC SUCCESSION: species composition is disturbed by environmental factors unrelated to the organisms present e.g. Hurricanes, forest fires, flooding, climate changes

• AUTOGENIC SUCCESSIONAUTOGENIC SUCCESSION: the changes in environmental conditions which leads to changes in species composition in an ecosystem are caused by the biological processes of the organisms themselves e.g. trees shading and killing plants underneath that require high sunlight [Includes Primary & Secondary Succession]Primary & Secondary Succession]

Allogenic Succession

• Serial replacement of species, driven by changing external changing external geophysical processesgeophysical processes

• Examples:– silt deposition in a pond, changing it

from an aquatic to a terrestrial habitat– increasing salinity of a sea– climate change

Autogenic Succession

• Change of species driven by biological processes changing biological processes changing conditions and/or resourcesconditions and/or resources

• Examples:– organisms living, then dying, on bare

rock– trees shading and killing plants

underneath that require high sunlight

Primary Succession

Primary SuccessionPrimary Succession::

• Occurs on barren habitats e.g. rock, sand, clay, ice this means that there is NO NO SOILSOIL present

• Pioneering organisms colonise and modify the environment until new niches occur

• Slow process - may take thousands of yearsTimeUnstable

PIONEERCommunity[lichens, mosses]

Stable CLIMAXCommunity[Trees]

Secondary SuccessionSecondary SuccessionSecondary Succession::

• Occurs where an existing community has been cleared by some disturbance. TOP TOP SOIL PRESENTSOIL PRESENT

• Disturbance can be either natural e.g. forest fire, hurricane or man-made e.g. deforestation, agriculture

• Faster than primary succession

• Pioneer communities tend to be annual plants

Time

In 1850, Connecticut was almost entirely open land cleared for farming or timber. Today, Connecticut has been mostly reforested through the process of secondary succession as farming has left the state since the 1800's

This area has not been cleared in over fifty years. These trees

represent the CLIMAX COMMUNITY for the rainfall, temperature and soil of this

area

This area has not been has not been mowed in about ten years. Shrubs and evergreen trees have moved in. These

are the INTERMEDIATE species

This area has been mowed within the last year. The plants are all annuals or herbaceous perennials.

These are the PIONEER species

Pioneer Species• Pioneer species initiate recovery

following disturbance in both primary AND secondary successions

• Pioneers "pave the way" for later colonists by altering the biotic and abiotic environment:– soil quantity, quality & depth

– increased moisture holding capacity

– light availability

– temperature

– exposure to wind

• Examples: Lichens and mosses

3.3. DEGRADATIVE DEGRADATIVE (HETEROTROPHIC)(HETEROTROPHIC) SUCCESSION:SUCCESSION:

• Sequence of changes associated with DECOMPOSITIONDECOMPOSITION processes

• When organisms die and begin to decompose, a repeated sequence of species appears, characteristic of the organism

• Since no autotrophs (green plants) are involved in this process, it is also known as HETEROTROPHIC HETEROTROPHIC

SUCCESSIONSUCCESSION

Example:When an animal dies, bacteria immediately start breaking down the organic materials. This produces a smell which attracts insects such as flies who lay their eggs on the body. Within a few hours the flies' eggs have hatched and the larvae (or maggots) begin to feed on the animal's soft tissue. Several types of beetle also feed on the dead remains, lay eggs and, when hatched, these larvae will feed on the dead remains as well. Now spiders begin to approach, not to feed on the dead animal, but to feed on the insects which are on the animal's body. The fact that degradative succession always occurs in the same sequence is used by forensic entomologists. These scientists can tell approximately when a victim died because of which insects inhabit the body when it is found

Changes in the complexity of ecosystems

• As succession takes place, the ecosystem tends to become more COMPLEXCOMPLEX and more STABLESTABLE

• Human activities, as well as natural disasters, can reduce the complexity in ecosystems. This reduction in complexity is shown by, for example, a reduction in the number of species present, a decrease in the number and variety of habitats and niches and a decrease in the complexity of food webs

CHANGES IN ECOSYSTEM COMPLEXITYCHANGES IN ECOSYSTEM COMPLEXITY

Increase in complexity shown by:

Number of species

Population size

Biological Productivity

Habitat/Niche Variety

Complexity of Food Webs

Loss of complexity caused by:MonocultureEutrophicationToxic PollutionOxygen depletion

AUTOGENIC SUCCESSIONALLOGENICSUCCESSION

DEGRADATIVE SUCCESSION

Geophysical Forces(e.g. Climatic Extremes)

Associated with Decomposition

Primary Secondary

Barren Land

Colonisation by PioneerSpecies e.g. moss, microbes

Disturbance of Existing Community

Intensive food production

• In 1999, the human population reached 6 billion• It is estimated that by 2050 this figure will increase to

9.4 billion• Sustaining this huge and ever increasing population

would not be possible without agriculture. According to the World Health Organisation, over 3.5 million tonnes of food are required every day to provide the minimum calorific intake for today's population and this needs to increase by 83,000 tonnes daily to accommodate the increasing population

• Since only 11% of land surface is suitable for agriculture, the growing demand for food can only be achieved by increasing productivity

Effects of intensive food production :

MONOCULTURE• Agriculture or forestry in which a single

species is cultivated over a large area for ECONOMIC EFFICIENCYECONOMIC EFFICIENCY

• With increased mechanisation and additional use of FERTILISERSFERTILISERS and PESTICIDESPESTICIDES, farmers can manage larger areas of land

• Crops are selected for their PRODUCTIVITYPRODUCTIVITY (speed of growth/yield) or DISEASEDISEASE RESISTANCERESISTANCE

Problems With Monoculture

• The farmer is dependant on fertilisers, fuel, machinery and seed

• Biodiversity is reduced to maximise crop yield by:

• REMOVAL REMOVAL ofof HEDGES HEDGES – loss of shelter– loss of shelter• USE ofUSE of HERBICIDES & PESTICIDES HERBICIDES & PESTICIDES• FERTILISERS FERTILISERS (can be toxic to other (can be toxic to other

species)species)

• By removing natural trees, shrubs etc nutrients can easily leak out of the soil : LEACHINGLEACHING

• Simplified ecosystems are vulnerable to difficulties as they represent dense numbers of HOSTSHOSTS of parasitic or disease-producing organisms

• E.g. the Irish potato famine of the 1840s was due mainly to the crop’s susceptibility to a particular mould

• Advantages due to diversity and physical separation are lost

RESULTS IN:- Potential for mass explosion of pests- Over reliance on PESTICIDES- This can lead to genetic resistance in pest species … loss of control!

Eutrophication• As a result of human

activities, sometimes waterways can be polluted by EXCESSEXCESS NUTRIENTSNUTRIENTS such as NITRATESNITRATES and PHOSPHATESPHOSPHATES

• These activities include: – runoff of animal waste from

farms

– leaching of fertilizer from agricultural areas

– the addition of untreated sewage

• This leads to an explosion in the growth of algae producing algal blooms

Oxygen Depletion• Although these algal blooms may increase

oxygen levels in the water during the day, OXYGEN DEPLETIONOXYGEN DEPLETION will occur at night as a result of RESPIRATIONRESPIRATION

• As the algae die they accumulate at the bottom of the lake, greatly increasing the number of decomposer organisms, which deplete the oxygen levels further

• This leaves little oxygen for larger animals which die

• Eventually species diversity in the water is drastically reduced

Toxic pollution

• Pesticides and herbicides also contain substances which are toxic to organisms other than those they are intended to kill

• As well as these substances, many industrial sites are polluted with toxic heavy metals such as LEADLEAD, , CADMIUMCADMIUM and MERCURYMERCURY

Major types of Toxic Pollutants

• A variety of these toxic chemicals, including unnatural synthetics, have been and are dumped into ecosystems

• Many cannot be degraded by microbes and persist for years or decades

• Some are harmless when released but are converted to toxic poisons by reactions with other substances or metabolism of microbes

• Organisms acquire toxic substances along with nutrients or water, some of which accumulate in their tissues.

Biological Magnification

• This is the process by which toxins e.g. mercury, poisons, become more and more concentrated with each successive link in a food chain

• BiomagnificationBiomagnification results from biomass at each trophic level being produced from a much larger biomass ingested from the level below. The top-level carnivores are usually most severely affected by toxic compounds released into the environment

Example: DDT

• The pesticide DDT was used to control mosquitoes and agricultural pests

• DDT persists in the environment and is transported by water to areas away from the point of application

• Because it is soluble in lipids and collects in fatty tissues of animals, the concentration is magnified at each trophic level and reached such high concentrations (10 X 106 increase) in top-level carnivorous birds that calcium deposition in eggshells was disrupted

• Reproductive rates declined dramatically since the weight of nesting birds broke the weakened shells

Nuclear Waste

• The release of radioisotopes by nuclear accidents and the unsafe storage of nuclear wastes also present a serious environmental threat

• These contaminants can last for many years due to long half-lives and are also subject to biological magnification

Biological Monitoring• An INDICATOR SPECIESINDICATOR SPECIES gives

information about the environment in which it is living

• Species that are known to be sensitive to certain environmental conditions or pollutants can be used to determine the state of an ecosystem by their presence or absence from it

• Although all species indicate something about the environment in which they live, a few key species are generally used as indicator species e.g.

Biochemical Oxygen Demand (BOD)

• Oxygen depletion caused by aerobic decomposition seriously affects the freshwater ecosystem

• The extent of this pollution can be assessed using the BIOCHEMICAL OXYGEN DEMAND (BOD)BIOCHEMICAL OXYGEN DEMAND (BOD) test that measures the amount of dissolved oxygen in water

• The BOD test is a mandatory water quality test used to estimate the amount of biodegradable organic material there is present in water

• A HIGH BODHIGH BOD indicates a HIGH LEVELHIGH LEVEL of organic pollution in the water. As there is a significant amount of organic matter present in the water a lot of oxygen is required by the micro-organisms to degrade it. A LOW BODLOW BOD indicates a LOW LEVELLOW LEVEL of organic pollution in the water. Less oxygen is required by the micro-organisms because less organic matter is present in the water

The mass of dissolved oxygen, in grams per cubic metre or milligrams per cubic decimetre, taken out of solution by a water sample incubated in

darkness at 20°C for five days

BOD of a river

Increase in Energy Needs

• The biological world is driven on almost entirely on SOLAR RADIATIONSOLAR RADIATION captured by plants

• Major sources of primary energy for humans: FOSSIL FUELS, NUCLEAR FUELS FOSSIL FUELS, NUCLEAR FUELS and and HYDROPOWERHYDROPOWER

• Each form of energy generation has its own environmental consequence

• Renewable energy sources harness energy without depletion e.g. SOLAR, SOLAR, WIND, WAVE, HYDROGEN, BIOMASS WIND, WAVE, HYDROGEN, BIOMASS ENERGY PRODUCTIONENERGY PRODUCTION

Environmental Consequences

• Intensive production of potentially toxic waste

• Fossil fuels are finitefinite and must be conserved• Burning of fossil fuels produce many

polluting gases:– SULPHUR DIOXIDESULPHUR DIOXIDE– NITROUS OXIDENITROUS OXIDE– CARBON DIOXIDECARBON DIOXIDE– WATERWATER– METHANEMETHANE– CFCsCFCs

• The release of ‘greenhouse gases’ increases the vital, natural greenhouse effect leading to global warming and thus climatic change

ACIDIC GASES

GREENHOUSE GASES

The Greenhouse Effect• The greenhouse effect is a natural

phenomenon and is responsible for maintaining the planet’s temperature 33°C higher than would otherwise be the case, thus allowing life to exist

• It is caused when sunlight reaches the Earth’s surface, which is converted into heat. This heat is re-radiated back into space in the form of infra-red radiation

• Although visible light passes through the atmosphere, some of the infra-red radiation is absorbed by the so-called greenhouse gases

• Carbon dioxideCarbon dioxide is the more important greenhouse gas

• Its contribution is more than all the other greenhouse gases put together

Relative contribution of gases to the greenhouse

effect

Because of the huge increase in the production of greenhouse gases in the last 150 years or so, the greenhouse effect is

increasing and this is thought to be contributing to GLOBAL GLOBAL WARMINGWARMING. Why is this important?

                                                                                    

              

Global Warming• The biological effects of the resulting climate

change will have an profound effect on ecological niches and the species that live in them

• Rising global temperatures will bring changes in:

– Weather patterns (warmer temps, wetter winters, drier summers, less snow)

– Polar ice caps melting leading to rising sea levels & flooding of coastal areas

– Increased frequency and intensity of extreme weather events (hurricanes, floods, droughts)

– Food shortages– Increased spread of disease e.g. malaria

Climate change is already happening!

• Globally, the ten hottest years on record have all occurred since the beginning of the 1990s

• Current climate models predict that global temperatures could warm from between 1.4oc to 5.8oc over the next 100 years, depending on the amounts of greenhouse gases emitted and the sensitivity of the climate system

Example: CORAL BLEACHING• An example of the effect of increasing temperature on

organisms is exemplified by the phenomenon known as coral coral bleachingbleaching

The zooxanthellae provide the coral polyps with nutrients produced by photosynthesis which, along with the nutrients the polyps gain by preying on tiny planktonic organisms, enables the coral to grow and reproduce quickly enough to produce reefs. The coral in turn provides the algae with a protected environment and a steady supply of carbon dioxide for photosynthesis. The tissues of the corals themselves are transparent - their colours come from the zooxanthellae living inside them.

Under stress e.g.rise in sea temp, corals expel their zooxantheallae, which leads to a lighter or completely white appearance, hence the term "bleached"

The corals that form the structure of the great reef ecosystems of tropical seas depend on a symbiotic relationship with photosynthesizing unicellular algae called ZOOXANTHELLAEZOOXANTHELLAE that live within their tissues

End of UNIT 2 !!!

• Watch DVDs:An Inconvenient Truth’ : Climate ChangePlanet Earth: The FutureBlue Planet : Deep Trouble

• NAB & A/B Test: Thursday 19th Feb