Higher Biology

1
Higher Biology

• Adaptation
• Part 5

2
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.

3
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
gt
Energy Used up
4
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

5
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.

6
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).

7
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.

8
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.

9
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.

10
Bees

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

11
Economics of foraging

• Foraging is economic when
• E.g.

Energy Gain
gt
Energy Used up
Energy used in finding, catching eating food
risk of being killed by a predator during feeding
Energy Gain
lt
12
Economics of foraging

• Factors that affect foraging include
• Time- search time -to locate
• pursuit 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.

13
Economics of foraging

• 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.

14
Economics of foraging

• 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.

15
Economics of foraging

• Density and size of prey -
• There is an optimal size of prey which will
  provide a net energy gain.

16
Economics of foraging

• 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.

17
Competition

• Competition occurs when resources are in short
  supply.
• There are 2 types of competition
• Interspecific
• Intraspecific

18
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.

19
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.

20
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.

21
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.

22
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.

23
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.

24
Advantages of Dominance hierarchy

• Aggression between members becomes ritualised.
• Real fighting is kept to a minimum.
• Serious injury is normally avoided.
• Energy is conserved.
• Experienced leadership is guaranteed.
• The most powerful animals are most likely to pass
  their genes onto the next generation.

25
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.

26
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
• Larger prey can be tackled and so more food can
  be gained.
• All members, including the subordinate, benefit-
  although the dominant ones will get the larger
  share of food.

27
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.

28
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.

29
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