Higher Biology

AdaptationPart 5

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Adaptation 5

By the end of this lesson you should be able to:

Explain what foraging behaviour is. Explain the purpose of search patterns to animals. Describe the economics of foraging behaviour. Understand what is meant by optimal foraging. Know the difference between interspecific and intraspecific competition. Explain the advantages of dominance hierarchy. Explain the advantages of co-operative hunting. Explain territorial behaviour in animals in relation to competition for food.

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Foraging behaviour Foraging is the term given to the ways in

which animals search for food. Searching for food requires energy. It is important that the energy gained from

the food is greater than that involved in finding/catching it.

Foraging behaviour has evolved so that

Energy Gain > Energy Used up

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Search Patterns Some animals have evolved specific search

patterns to help them find food with the least energy cost to themselves.

E.g. Planaria Ants Bees

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Planaria

This is a type of flatworm which lives in ponds and streams and feeds on the remains of dead animals!

They are able to move about freely and change direction.

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Planaria

They tend to move about randomly in the absence of food- to increase the overall area covered and so the chance of them finding food.

Can detect chemicals coming from dead animals using chemoreceptors so move towards them (down a concentration gradient).

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Ants

Ants leave the colony and wander about backwards and forwards searching for food.

As soon as an ant finds a food source, it immediately makes its way back to the colony, marking its trail with scent.

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Ants

Other ants can then follow the trail and reinforce the scent marks as long as the food lasts.

As the scent marks quickly fade, no energy is wasted following old trails.

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Bees

Bees are social insects and the colony is dependent on a regular food supply.

Once a worker bee has located a good food source, she returns to the hive and performs a waggle dance which indicates the distance and direction of the food to other workers.

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Bees

The duration of the dance indicates the richness of the food and will reduce as the richness of the food reduces.

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Economics of foraging Foraging is economic when:

E.g.

Energy Gain > Energy Used up

Energy used in finding, catching

& eating food; risk ofbeing killed by a predator

during feeding

< Energy Gain

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Economics of foraging

Factors that affect foraging include:

1. Time- search time -to locatepursuit time -to chase, catch & kill

If the search time is short and pursuit time is long, then animals tend to be selective e.g. lions can easily find herds of zebra, however to catch one would take time, so the lion would select an older or weaker zebra as its prey.

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Economics of foraging

1. Time- If the search time is long but pursuit time is short, then animals tend not to be selective.

e.g. an anteater may take ages to find an ant colony, however once it has, it tries to eat as many ants as it can, as quickly as possible.

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Economics of foraging

2. Density and size of prey - If the density of prey is low then

predators will be less selective about what it eats. (& vice versa)

If the prey is small and will not yield much energy then predators will be less selective about what it eats.

If the prey is large then more energy will be spent in catching the prey and it may not be economical.

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Economics of foraging

2. Density and size of prey - There is an optimal size of prey which

will provide a net energy gain.

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Economics of foraging

3. Risk of injury - It can be better for herbivores to

settle for food in poorer ecosystems rather than foraging in a food-rich area which exposes them to attack by predators.

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Competition

Competition occurs when resources are in short supply.

There are 2 types of competition:1. Interspecific2. Intraspecific

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Interspecific Competition

This is between individuals of different species which occupy the same ecological niche.

Usually one species ousts the other and so the loser must migrate or face extinction.

E.g. red and grey squirrels rainbow trout and native brown trout Usually a compromise is reached where

the rivals might eat different foods, or eat at different times of day. Etc.

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Intraspecific Competition This is between individuals of the same

species which occupy the same ecological niche.

The members of the same species will need exactly the same resources.

Intraspecific competition is even more intense than interspecific competition.

Intraspecific competition can be reduced by types of social behaviour.

e.g. dominance hierarchy, co-operative hunting, territorial behaviour.

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Dominance hierarchy This is the type of behaviour occurring

in higher animals living in social groups. It is based on aggressive behaviour

between individuals which results in a ranking order, where the higher rank animals dominate those of a lower rank.

E.g. in birds like hens or pigeons one bird will emerge as being dominant and will peck and intimidate others in the group.This creates a pecking order.

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Dominance hierarchy Another example in mammals is

wolves. Wolves hunt in packs and dominance

hierarchy exists amongst the females. When there is plenty of food- the

dominant female mates and allows others to mate as well.

However when food is scarce- the dominant female will mate, but allow fewer of the others to mate.

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Dominance hierarchy This ensures that the dominant females

young will have enough food and be more likely to survive.

The dominant individual ensures its high rank by a system of aggressive or threat displays.

E.g. raising head and staring at other animals

baring their teeth raising their ears fur, ears & tail upright.

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Dominance hierarchy All these gestures make the wolves

appear larger and more threatening. The other individuals show subordinate

displays. E.g. lowering eyes and head covering their teeth lowering their ears fur, ears & tail lowered.

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Advantages of Dominance hierarchy

1. Aggression between members becomes ritualised.

2. Real fighting is kept to a minimum.3. Serious injury is normally avoided.4. Energy is conserved.5. Experienced leadership is guaranteed.6. The most powerful animals are most

likely to pass their genes onto the next generation.

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Co-operative hunting Predatory animals may hunt co-

operatively to optimise energy gain. Prey will be larger and less energy will

be used to secure the kill. The kill will then be shared between all

members of the group, even subordinate members.

Subordinate members will therefore gain more food by foraging alone.

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Co-operative hunting E.g. wild dogs communicate with each

other using calls and body postures. They hunt in packs of 6-30 animals,

roaming over large areas in search of prey like gazelle or zebra.

Advantages:1. Larger prey can be tackled and so more

food can be gained.2. All members, including the subordinate,

benefit- although the dominant ones will get the larger share of food.

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Territorial behaviour A territory is an area that an animal

defends, usually against members of its own species.

The territory has to contain enough food for himself and eventually a mate and their young.

Territories are defended aggressively by social signals.

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Territorial behaviour E.g. a robin sings to proclaim the

boundaries of its territory. Male lions defend the pride against

intruders- they mark boundaries with urine and patrol them regularly.

The size of a territory depends on the species of animal and the resources available.

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Adaptation 5

Can you do it?

Explain what foraging behaviour is. Explain the purpose of search patterns to animals. Describe the economics of foraging behaviour. Understand what is meant by optimal foraging. Know the difference between interspecific and intraspecific competition. Explain the advantages of dominance hierarchy. Explain the advantages of co-operative hunting. Explain territorial behaviour in animals in relation to competition for food