Unit 1 Environment and Response

Learning Outcomes – On completing this unit you should be able to: Explain the contribution that responses to environmental factors make towards the

survival of individuals and species Define and give examples of abiotic and biotic environmental factors Define key terms relating to the environment and the reaction of living things to

environmental factors

ENVIRONMENTAL FACTORS The environment is all the external conditions affecting the life of an organism. The

environment is made up of non-living (abiotic) and living (biotic) factors, many of which are constantly changing. For the individual and also the species to survive they must be able to respond to changes within their environment.

Abiotic Factors

These are the physical factors such as gravity, light, temperature, water, sound, wind, fire and substrate. How an organism responds to abiotic factors is a major factor in its survival. A plant shoot may grow up way from the gravitational pull and towards light so that it can take full advantage of the sunlight for photosynthesis. A slater may respond to light or low humidity in a way that reduces water loss.

An environmental cue or signal that starts a process is usually an abiotic factor such as day length that initiates the flowering process in some plants. A visual cue might be trees near a bee hive that the bees use to find their way home.

Biotic Factors

Interactions with other organisms of either the same (intraspecific) or different (interspecific) species happen in many different ways.

Intraspecific interactions include: Competition for resources where the demand is greater than the supply, for example,

food, nesting sites, space, water, nutrients Cooperation such as wolves hunting in a pack, or slaters clumping to reduce water loss. Aggression, for example a Pukeko defending its territory Reproduction, for example, pair bonding behaviour in birds

Interspecific interactions include: Competition for the same resources, although this is not usually as intense as between

members of the same species Cooperation which means that members of each species benefits, this is called

mutualism, for example, stinging ants protecting South American vines. The ants benefit from the sugary secretions produced by the plant.

Exploitation is where the members of one species benefit at the expense of another. This includes predators catching and eating prey, herbivores grazing on plants and parasitism.

Commensalism which means “taking without harming” is where one organism benefits while the other is neither harmed nor helped. For example epiphytes which live on the branches of trees and gain the advantage of being closer to the light and perhaps more rainfall, while the tree is apparently unaffected.

Summary of interspecific interactions

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Interaction Effect on species 1 Effect on species 2Predation of species 2 by species 1

Beneficial (+) Harmful (-)

Mutualism + +Commensalism of species 1 with species 2

+ No effect (0)

Parasitism by species 1 of species 2

+ -

Competition between species 1 and 2

- -

Each organism has its own role within the community of plants, animals and micro-organisms where it lives. This is called its ecological niche and includes what it eats, what eats it, how it responds to all the varying environmental factors. This is different from its habitat, which is where it lives, its physical surroundings. For more details of ecology refer to Biology year 12 in this series.

ADAPTATIONS

Plants and animals have physical, physiological (functional) and behavioural adaptations to environmental factors. The development of melanin in the human skin is a physiological adaptation to the hot sun whereas seeking shade is a behavioural adaptation. Adaptations are features that help an organism survive.

Natural Selection will weed out those that are less well adapted for the environment in which they live.

Relatively rapid responses to environmental changes are called “behaviour” in animals. These responses in both plants and animals are caused by the organism detecting an environmental change (stimulus) using a receptor such as eyes in an animal or a light absorbing pigment in plants, the message that has been received being transferred to the part of the organism that will respond such as the legs of an animal or the expansion zone in a plant shoot, where the response will take place

TYPES OF BEHAVIOUR Animal behaviour can be divided into two main types: innate which means “born with”

and learned which results from experience. Innate behaviour is controlled by the genes although the behaviour may be modified by

experience. Examples are reproductive, cooperative, and group behaviour. Learned behaviour may also be under some genetic control because how well an

organism learns is usually genetically controlled. Examples are trial and error, conditioned, insight and habituation behaviour.

Key Points Summary

The environment is all the external conditions affecting the life of an organism. The environment is made up of both abiotic and biotic factors Biotic factors are made up of interactions with members of the same species

(intraspecific) or different species (interspecific) Living organisms have physical, physiological and behavioural adaptations to

environmental factors. These features help them survive Animal behaviour can be divided into innate and learned.

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Unit 1: Environment and Response

ASSESSMENT ACTIVITY

Matching key terms with descriptions

a) Where an organism lives, its physical surroundings

mutualism

b) The role of an organism within its ecological community

Learned behaviour

c) Relatively rapid responses in animals to changes in the environment

intraspecific

d) Physical environmental factors such as light, gravity

interspecific

e) Living environmental factors such as other animals

Innate

f) Interactions with organisms of the same species

Habitat

g) Interactions with organisms of another species

environmental cue

h) Interaction between organisms where one benefits while the other is not affected

environment

i) Features that help an organism survive Ecological nichej) Cooperation between members of two different species where both benefit

Commensalism

k) Animal behaviour that is learnt by experience

biotic

l) Animal behaviour that is “in-born” and genetically controlled

Adaptations

m) All the external conditions affecting an organism

Behaviour

n)A signal that starts a process such as exposure to long days initiating flowering

abiotic

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Unit 1: Environment and Response

ANSWERS

Matching key terms with descriptions

a) Where an organism lives, its physical surroundings

habitat

b) The role of an organism within its ecological community

ecological niche

c) Relatively rapid responses in animals to changes in the environment

behaviour

d) Physical environmental factors such as light, gravity

abiotic

e) Living environmental factors such as other animals

biotic

f) Interactions with organisms of the same species

intraspecific

g) Interactions with organisms of another species

interspecific

h) Interaction between organisms where one benefits while the other is not affected

commensalism

i) Features that help an organism survive adaptations j) Cooperation between members of two different species where both benefit

mutualism

k) Animal behaviour that is learnt from experience

learned behaviour

l) Animal behaviour that is “in-born” and genetically controlled

innate

m) All the external conditions affecting an organism

environment

n) A signal that starts a process such as exposure to long days initiating flowering

environmental cue

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ANIMAL BEHAVIOUR AND PLANT RESPONSES

The environment includes both living (biotic) and non-living (abiotic) factors that affect the lives of plants and animals.Both can act as stimuli which produce responses in living organisms.

ABIOTIC FACTORS: these are the physical factors e.g.

Light (photo-) e.g. colour, intensity, direction - produce diurnal rhythms, reproductive cycles, photosynthesis in plants Gravity (geo-) orientation in space, direction of growthTemperature (thermo-) this may affect the speed of reactions within organisms, and determine the range where a species can liveWater (hydro-) e.g. humidity; soil moisture; water current, speed, salinity, turbidity; average rainfall. All plants and animals need water!Chemicals (chemo-) e.g. essential mineral nutrients, carbon dioxide, oxygen, also poisonsTouch (thigmo-) living things need to respond when they come up, against a solid object!Sound e.g. pitch, loudness, range, may be communication, response to danger, used for tracking preyPressure especially important to living things in the ocean, up in the air.Wind e.g. velocity, direction, gustinessSubstrate e.g. rock, sand, mud, silt - important for burrowing animals and plantsFire in most environments fires have always started naturally by lightning or volcanic action.

BIOTIC FACTORS

Intraspecific Interactions - with individuals of the same species.

e.g. competition for the same resource such as light, food, space, water, breeding sites reproduction - availability of mates, competition for a mate, courtship, pair bond

formation, parental care aggressive interactions including territory formation and hierarchies co-operative interactions - e.g. group formation for defence, hunting

Interspecific relations - interacting with individuals from other species e.g.

competition for the same resources such as food, water , space, light (competition is never as intense as between members of the same species - why?)

Animal/plant relationships e.g. browsing, grazing Succession - replacement of one species by another over time Stratification - vertical relationship with other organisms ( in space) Animal/animal and plant/plant relationships e.g. mutualism, commensalism, antibiosis,

exploitation (predation and parasitism) and competition

(check you know what these mean, p. 3 Designs of Life)

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BEHAVIOUR

This is an organism’s response to signals (stimuli) from the environment (both biotic and abiotic).

Environmental stimulus

Receptor detects stimulus

(Communicating system e.g. nerves, hormones)

Co-ordinating system

Other info

Effector responds e.g. muscles contract

It’s all in the timing

Individual organisms need to synchronise their activities with environment including other organisms.

It is a waste of time being ready to mate when all the other members of your species are not! Even if you are a plant, it may be a waste of time producing flowers, if no other plant of your species is doing it.

So ... organisms need to tell the time!

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BIOLOGICAL TIMING

Organisms, even unicellular, have internal clocks which can measure the passage of time. Many of the cyclic behaviours we see are governed by these internal clocks which are generally ‘reset’ (the process is called entrainment) by environmental cues (called zeitgebers) such as night/day, day/night length.

These cyclic behaviours continue even if we keep the environment the same e.g. continuous night. They are called ‘endogenous rhythms’. The cyclic behaviour occurring in the absence of external cues is termed ‘free running’.

Some cyclic behaviours may be only determined by changes in the environment. These are called ‘exogenous’.

Circadian rhythms are responses to day and nightPeriod of cycle about a day

Circannual rhythms are responses to..................................Period of cycle .............................................

Circalunar rhythms are .......................................................Period of cycle...............................................

Types of circadian rhythms:

Diurnal which means active during the day timeNocturnal which means...................................................Crepuscular .....................................................................

*Look up examples showing each type

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ORIENTATION RESPONSES

Tropisms: growth towards or away from a unidirectional stimulus Taxes: movement of the whole organism towards or away from a unidirectional stimulus Nastic response: response of plants to a stimulus unrelated to direction e.g. opening and

closing of flowers ( not strictly an orientation response?) Homing: returning of the organism to the home area Migration: Annual mass movement of animals from breeding areas to non-breeding

areas.

* Try the self check p6-7

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ANIMAL BEHAVIOUR AND PLANT RESPONSES SEMINAR

Choose an example of an animal behaviour or plant response to the environment. Describe the stimulus, the behaviour/response, the mechanism. Use a named example to illustrate. Prepare short, written notes for the class, followed by 2-3 questions.

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HOW DO PLANTS TELL THE TIME?

Plants show many circadian responses such as opening and closing of flowers, timing of nectar secretion, lowering of leaves etc. Some are control by an endogenous rhythm such as the lowering of leaves in beans.

Annual rhythms e.g. flowering, dormancy, abscission of leaves (falling off).

Plants need to know when to start initiating the production of flower buds, which happens quite a time before the time of flowering. Some plants flower in the spring, some in the summer and some in the autumn. Some plants (generally from the tropics) flower all the year round.Plants determine when to flower by measuring the length of darkness (night). This is done by a pigment called PHYTOCHROME which exists in two forms:Red light absorbing (P665)Far-red light absorbing (P725)

(called P665 as the most effective light absorbed was 665 nm)

When the P665 form absorbed red light (or normal sunlight which contains a high concentration of red) it is quickly change to the P725 form. This form slowly changes back to the P665 form in the dark. When scientists shone far red light (725nm) on the P725 form it quickly changed back to the P665 form. But this doesn’t happen in nature.

Day or red light(rapid)P665 P725

Far-red light (fast)

Night (slow)

It seems that the slow conversion of the P725 form back to the P665 form at night is what the plant is using as a timing device. The day is long enough, P725 accumulates and “long day” plants flower (those that flower in the summer), if the night is long enough all the P725 is changed to P665 and “short day” plants flower.

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Do plants relate to other plants?More often than you might think!

Allelopathy (= other suffering) Plants stop other plants growing near them and competing for resources by secreting poisonous substances. e.g. Walnut trees and Macrocarpa.

Seed dispersal allows the parent plant to reduce competition with and between their offspring. (revise this)

Stratification Vertical layers, the dominant species affects the conditions of other plants etc. (Revise this)

Epiphytes (e.g. of Commensalism) Plants grow on other trees and get more light and space etc. The host plant is not affected.

Plant parasites live on other plants and grow small “roots” called haustoria into the phloem of the host to get food. To be a obligative parasite the plant will not make its own food, e.g. dodder that grows on gorse. Hemiparasites also make their own food and have green leaves e.g. mistletoe

Lianas Climb up tall trees for the same reasons as epiphytes. They get advantages of height without having to expend the energy to grow their own strong trunk.

Relationships with fungi or bacteriaPlants not only have relationships with other plants but also members of other groups (check classification)

Mutualism e.g. legumes and Rhizobium bacteria that infect root nodules and fix atmospheric nitrogen. This also benefits other plants living nearby.e.g. many plants especially trees such as pine trees have mutualistic relationship with mycorrhizal fungi which infect the roots and send hyphae into the soil where they help the plant take up nutrients and food. The plant supplies protection and food. Uninfected plants do not grow very well.

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Do plants have relationships with animals?......... all the time

All animals depend on plants .. they either eat plants or they eat animals who have eaten plants, or have eaten animals that have eaten animals who have eaten plants!!

Some examples of herbivores are: Grazers eat pasture e.g. cows, browsers eat leaves of trees and shrubs e.g. giraffes Pollen feeders e.g. bees and birds Fruit eaters e.g. humans, birds, bats, rats.

Defence strategies!

Plants have developed many ways to defend themselves. e.g. thorns, divarication, toxic, bad tasting or sticky chemicals, stings, low growing points, seeds with hard shell or prickles etc.

Co-operating with animals Pollination by insects, birds, bats etc. Protection e.g. stinging ant colonies may protect a tree. Animals such as birds living in a

cactus may get protection from a plant. Seed dispersal e.g. seeds with small hooks or fruit eaten and seeds deposited with “compost”.

Some plants are completely dependent on one species of animal for pollination or seeds dispersal. If this animal becomes extinct so will the plant.

Some plants eat animals!These plants mostly live where nitrogen is in short supply such as bogs (no oxygen! and O2 is needed to fix nitrogen) or cracks in rocks and they use the protein from the animals to gain nitrogen e.g. sundew, Venus flytrap.

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ANIMAL RESPONSES TO THE ENVIRONMENT

1. What is an animal? ............................2. What is a mammal? ............................

Not all animals detect and respond to the same stimuli we do. A dog’s primary sense organ is it’s nose whereas for us it’s eyes!

3. Earthworms have no ears, eyes or nose. How do they manage to detect stimuli? ...........................................................................

PhotoreceptorsNot all photoreceptors are “eyes”. Earthworms just have photosensitive cells in their skin. There are two main sorts of eyes: eyes like ours that have a lens and provide a clear image. Some of these (like ours and other primates as well as birds) have colour vision but most mammals do not do not. The other main type of eye is a compound eye such as in insects. These have many separate parts called ommatidia each of which has a lens and it is thought that compound eyes produce a mosaic view of the words.

Heat (thermo) receptors

Some animals have special receptors which pick up infrared rays from warm objects e.g. snakes can get a good enough picture to attack prey just using infrared.

4. How do we detect heat? .............................

Mechanoreceptors (detecting touch, pressure, gravity, stretch , movement etc.)

Human skin has tactile (touch) receptors, internal organs have stretch receptors. Our inner ears contain gravity receptors. Other groups of animals have similar receptors.

Fish have a lateral line that responds to pressure changes in the water such as waves, currents and sound waves.

Chemoreceptors (smell and taste)

Detection of chemicals in air or water.

5. How are chemicals used by animals ? ......................................................................................................................................................

6. What are pheromones?..........................................................................

Sound (auditory) receptors

7. What is sound? .......................................

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In mammals such as humans the sound waves set up vibrations in the eardrum, these are magnified about 20 times by the ossicles (3 small bones) which then set up vibrations in the fluid in the inner ear. These vibrations move tiny hairs which are connected to nerve cells which send the message to the brain. Sound higher than human hearing is called ultrasonic. Many animals can hear and can communicate in the ultrasonic range. e.g. bats, insects, dogs, whales. Whales can also communicate in very low sounds (infrasound) that carry for kilometres.

Electric fields

This seems to be mainly (only) species that live in water. Some species can stun their prey and others detect disturbances in their electric field. Useful in muddy water or very deep, dark water. All living things create very small electric fields.

Magnetic fields

Birds such as homing pigeons seem to use the magnetic field lines of the earth to navigate. Not certain about other groups of animals.

8. What are orientation responses in animals? .....................................

9. Check you know about:- Taxes, kineses, homing, migration, methods of navigation.

BIOLOGICAL CLOCKS IN ANIMALS

Animals (and plants) show regularly repeated behaviours. These are called rhythms.

1. What is the difference between an exogenous rhythm and an endogenous rhythm? .......................................................

Revise/learn biological rhythms p 48-59 Designs of Life

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The Human Biological Clock

The Pineal gland (Master gland) secretes melatonin in the dark.

SCN are in the hypothalamus and are connected to the eyes. It is thought that they help reset the human biological clock.

The human biological clock, when free-running, has a day of about 251/2 hours, so it needs to be reset each day. It is mostly reset by light which resets the SCN (suprachiasmatic nuclei). This then tells the pineal gland to start or stop making the sleep inducing hormone, melatonin.

Circadian rhythms in humans

Humans have many rhythms such sleep/wake, body temperature changes, heart rate, pain perception, learning efficiency and many more. Read and make short notes about these e.g. p 49-56 “Designs of Life”

Lunar cycles, Yearly cycles , Hibernation, Aestivation, Reproductive cycles. Find out about these with 2-3 named examples of each.

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ANIMAL RESPONSES TO THE BIOTIC ENVIRONMENT.

These can be interspecific or intraspecific,aggressive or co-operative.

Aggressive Intraspecific behaviour

Aggression is belligerent behaviour that arises from competition.

1. Find out why animals fight and why it doesn’t usually lead to death. Use named examples. (p60).............................................

TerritoriesMany animals have territories. A territory is the area around their home/nest. Often there is a larger area surrounding the territory called the ‘home range’ where the animal will go regularly to find food etc.

2. Find out at least 8 reasons why having a territory is an advantage................................

Territories may be defended all year round or only in the breeding season.

3. Animals generally mark their territories. Give four named example of how this may be done...........................................................

Human territories ..is this the source of wars?Humans are naturally tribal or group living animals. Originally we lived in groups of less than 100 people and we knew each member individually. If the group was attacked everyone rushed to the defence. We also have family territory and personal space.

4. Do humans, like other animals, have rituals and territories that reduce the chance of damaging aggression? If so, what are they? and how do they affect our daily lives?

Hierarchies

Many social animals, including humans to a certain extent, have linear dominance relationships called a ‘pecking order’. This is where the top animal picks on the next in line and so on. Once the ‘pecking order’ has been worked out it is usually maintained by posture and displays rather than physically. Body language in cats, dogs, seagulls and pukekoes when meeting other animals can tell a lot about their social position.

1. Find out at least 2 named examples of animal hierarchies and explain how scientists use a chart to determine the order of dominance.

2. What are 2 body posture behaviours you have noticed in humans, and their ‘meaning’?

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Co-operative Intraspecific behaviour

Group formation can benefit a species in many ways;

Hunting e.g. wolves, lions, wild dogs. Defense - some animals can watch for danger while others feed e.g. baboons, prairie

dogs. Predators may be less likely to attack a group. Protection of weaker members e.g. dolphins help mothers and babies during birth and

help the injured.

1. How do baboons work together in a group and how does it benefit the species?

........................................................................

Social insects have a very specialised type of grouping where individuals are specialised for certain jobs either by having specialised body parts e.g. soldier ants or by taking on different jobs as they go through their life cycle e.g. worker bees. Honey bees have been closely investigated as they are very important to humans. Some bee larvae are fed royal jelly by the workers and these develop into queens. The first one to hatch kills the others. The new queen only mates once with a drone (male bee) and then spends the rest of her life laying eggs. Fertilised eggs turn into female bees (workers or new queens) unfertilised eggs become drones whose cells are all haploid. The queen controls the activities of the hive by pheromones which is passed from bee to bee.

Other groups.

Clumping e.g. woodlice to conserve moisture, birds to conserve heat

Flocking or shoaling of some birds and fish may confuse predators.

Breeding groups e.g. penguins, gulls , gannets. The safest spot is in the middle!

Courtship and pair bonding Courtship rituals are a way to reduce the chances of being attacked for coming to close and pair bonding is a way to make sure that the relationship lasts long enough to bring up the offspring safely. Some animals such as albatrosses and swans my mate for life. This reduces the amount of time and energy spent finding a new mate each season.

1. Find some named examples of courtship and pair bonding behaviour. .........................

Parental care is another type of co-operative behaviour. For a species to survive each generation must bring up the new generation.

Some species have no parental care but compensate by producing huge numbers of offspring e.g. most fish.

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Other species produce only a few offspring but invest much time and energy in feeding and protecting their young and in some cases e.g. humans, spending time teaching them the behaviour they need to survive.

Many species are part way between.

2. What are the disadvantages and advantages of producing thousands of offspring but not providing parental care? Think about the energy expended compared with the gains.

3. What about a small number of offspring and good parental care?

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INTERSPECIFIC RESPONSESAggressive responsesCompetition between animals is usually for resources such as food, water, breeding sites etc. The more scarce these become the more intense the competition.1. What is the ecological niche of an animal? ..........................................................

2. Explain how Gause’s principle relates to interspecific competition. .........................................................................

Predator/Prey relationships

In many interspecific interactions one animal is the predator and the other animal is trying not to be the prey!

Predators generally weed out the weaker and less well adapted prey and have a role in “improving” the gene pool as well as preventing the species over-running their own food source as happens with rabbits. If predators wipe out their prey they are cutting off their own food source.

Investigations of predator relationships are important when considering the effects of reducing prey numbers e.g. with RCD and rabbits. What else will the predators of rabbits such as feral cats, stoats and weasels eat (native birds?)

There are 3 major variables: Density, size and reproduction rate of the prey The predator/prey ratio Whether the predator would eat different prey if there is little food compared with what

it eats when there is plenty of food. e.g. feral cats might eat mostly rabbits when there are plenty but might eat native birds and their eggs if there are few rabbits.

Many factors need to be considered which mostly relate to how much energy is expended by the predator compared with how much it gains.

1. How are these factors involved in the energy balance? weather, size of predator and prey, endurance of the predator, social system. ........................................................................

Adaptations for getting other animals for food

1. Let the prey come to you! Find named examples for each of these:- Sifting the environment, Dangling bait, Making a web or trap, Lying in ambush....................................................................

2. Moving around to catch your prey. Prey usually don’t want to be caught and eaten and find many ways to avoid this fate. Predators need adaptations to cope!

Find named examples showing how predators cope with prey that are:-a) packaged or hidden to avoid being eaten......................................................b) large or in big groups.....................

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c) Give some examples of animals that use tools to catch their prey.............................

3. Or you could be a parasite!

Give some named examples of parasites. Explain the difference between a parasitoid and a parasite. ...........................................................................

4. Or you could just go to the supermarket and buy some sausages!

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HOW DO PREY STOP THEMSELVES BEING EATEN?

Defense strategies!

1. CamouflageVisual camouflage is the most common. Find named examples of: countershading, disruptive colouration, camouflaging eyes........................................................................

2. Blend and bluffCryptic colouration hides the animal against its background as long as it keeps still. If it is discovered it needs a method of scaring off the predator while it escapes. Find 2 named examples ...................................................................

3. Startle the predator e.g. many caterpillars have eye spots away from their head often only exposed when attacked.

4. Pretend to be inedibleMany animals imitate the look and behaviour of something inedible to the predator e.g. looking like a leaf and swaying in the wind. This is really an example of camouflage. Find two named examples ..........................................................................

5. Mimic another animal!a) Batesian mimicry: this is when a harmless animal looks like a dangerous or poisonous one. Explain how a named example does this. .......................................

b) Mullerian mimicry: this is where several poisonous species have similar warning colouration. e.g. striped snakes This means if a predator tastes one and is sick it won’t touch any others that look the similar.

6. Warn predators that you are dangerous or taste awful (aposematic colouration) with stripes (e.g. snakes or wasps) or bright colours (e.g. Monarch butterfly )

7. Warn predators by making a sound (aposematic sound). Explain how a named example does this. ..........................................

8. Chemical warfare! Find three named examples that do this. ....................................

9. Curl up into an impenetrable ball. e.g. armadillos, hedgehogs.

10. Saved by the shell! Find two named example of animals who protect themselves with shells. .....................................................

11. If all else fails .. hide! Find two examples! .......................................................

12. Safety in numbers: there are so many of you that the predator can’t eat more than a few of you, so most escape. Find 2 examples. .......................................................

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Sometimes the large numbers also confuse the predators which may not be able to pick out an individual to catch. e.g. shoals of fish.

14. Final resort: pretend to be dead. Many predators only catch live prey! Find 2 examples. .......................................................

CO-OPERATIVE BEHAVIOUR

Of course most co-operative behaviour between animals is between closely related animals of the same species because they share most genes in common. (*Background reading “The selfish gene”)

However some animals co-operate with animals from another species. Find named examples of Mutualism (both benefit) and Commensalism ( one benefits, other not harmed “eating from same table”) .........................................................................

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Orientation Responses

Learning outcomes: Explain how animals sense and respond to environmental stimuli List examples of common stimuli Describe how examples of receptors detect stimuli Explain the biological significance of animal orientation responses such as taxes,

kineses, homing, migration and navigation.Animal Senses

Animal behaviour is an observable response, a strategy for survival, so that the individual will survive long enough to reproduce.

Changes within the body or in the outside world that can be detected by the organism are called stimuli (singular: stimulus). In more complex animals many stimuli are detected by sense organs such as eyes and ears and the stimulation of the sense organs is often the starting point of an observable response that we called behaviour.

Light (photo) detectors

Most animals have photoreceptors which are cells or contain cells that are sensitive to light. Some invertebrates such as earthworms just have photoreceptor cells in the skin particularly near the front end of the body. They can only detect the general intensity of light.

Arthropods, for example crayfish and house flies, have compound eyes made of many individual units. Compound eyes are very good at detecting movement but are not so good at forming detailed images.

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Sound (auditory) receptors

Sound waves are pressure waves through a medium such as air, water, or the ground. To detect these waves something needs to be moved as they pass by.

Fish have a lateral line system along their sides that contains hair cells with hair-like projections that end in a jelly-like membrane that moves as the pressure wave passes. The other ends of the hair cells are connected to nerve endings which carry the message to the brain. This lateral line system is not found in land vertebrates. Fish can also detect pressure waves from a greater distance with similar receptors in their inner ear.

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Land vertebrates also detect sound by means of similar hair cell receptors in the inner ear.Gravity Receptors

To detect gravity something needs to “fall” and this movement needs to trigger a nerve message.

Most invertebrates have statocysts that have hair cells with the hairs or cilia embedded in a gelatinous membrane containing chalky granules. These granules make the membrane heavy enough to move if the animal changes its position relative to the gravitational pull.

Vertebrates have a similar system in the inner ear.

Chemorecptors Chemorecptors are used in detecting chemicals in the air (smell) and in food and

liquids (taste). Chemicals used to communicate between members of the same species are called

pheromones. These are often used to attract members of the opposite sex as in moths and may be detected a number of kilometres away.

Heat (Thermo) ReceptorsOther Receptors

Animal Responses When the sense organs detect a stimulus they send a message via the nerves to the

Central Nervous System (CNS) (brain and spinal cord) which will respond by sending a message back to an effector organ such as a muscle or a gland which will bring about an observable response such as a movement or an increase in secretion.

Orientation Responses

An orientation response is one where the animal can position itself in relation to a certain fixed point or stimulus.

Orientation responses can be simple responses to abiotic factors such as light, humidity or touch or they can be much more complex often involving long distances such as migration or homing.

Simple orientation responses Taxis (plural: taxes) is the movement of the animal towards or away from a stimulus that

is unidirectional (coming from one direction only). They are highly stereotyped and genetically programmed.

For example the movement of an earthworm away from light would be called “negative phototaxis”

Other examples of taxes are chemo- (chemicals), geo- (gravity), thermo- (heat), hydro- (water), thigmo- (touch). For each one, the movement of the animal may be positive (towards the stimulus) or negative (away from the stimulus). A mosquito may show positive thermotaxis and move towards a human body!

Kinesis (plural: kineses) is the nondirectional or random movement response of an animal to a stimulus which may or may not be directional.

Orthokinesis is where the rate of movement speeds up as the intensity of the stimulus increases, for example, slaters will move faster, the brighter the light. This allows them to end up in a darker place because as soon as they reach darkness they slow down. This is an advantage because slaters become dehydrated very easily when exposed to warm sunlight and die. Kineses are NOT positive or negative.

Klinokinesis is where the rate of turning increases as the intensity of the stimulus increases. This often happens at the same time as orthokinsis.

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Complex Orientation Responses:

Migration

Animal migrations are regular, generally annual, movements of large groups of animals from a place where they breed to another place where they do not breed but usually just feed. They then move back again to their breeding place.

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Homing Homing generally refers to the ability of animals to find their way home, in particular,

over unfamiliar territory. Navigation – finding the way

Migrating and homing animals need to be able to find their way, often over thousands of kilometres of unknown territory. How do they do it?

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Tropisms

To explain tropisms scientists had to find what the stimulus was, what detected the stimulus, what transferred the message from the point of detection to the point of response and what the response was!

1. For phototropism find out:

The answers to each of the questions and how it was found out and who did it! Perhaps summarise your information in a table.

2. List the other main tropisms, what the response is to and what is known about the mechanism.

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