Optimal Foraging

Question 1

What are the two perspectives of optimal foraging?

Answer 1

Individual and group

Question 2

Why is optimal foraging such an important aspect of behaviour?

Answer 2

Energy - need a positive energy balance where input exceeds output

Question 3

What are some energy inputs?

Answer 3

Feeding

Question 4

What are some energy outputs?

Answer 4

Homeothermy
Homeostasis
Resource defence
Sex
Rearing offspring

Question 5

How do animals minimise energy output?

Answer 5

Feeding efficiently through optimal foraging

Question 6

Which two factors may affect individual economic decisions?

Answer 6

Food quality (size, nutrition, number)
Time (searching, handling, commuting)

Question 7

What is an example of when an animal has had to make economical decisions?

Answer 7

Optimal load carrying in starlings - central place foraging: the starling should take back as much food from each trip to maximise the rate of food delivery to its young

Question 8

What two things do the optimum number of prey depend upon?

Answer 8

Search time and commuting time

Question 9

How was the hypothesis “change in commuting distance changed the optimum number of prey” tested?

Answer 9

Known number of birds in a wood, commute length and food patch richness
Used nest boxes, electronic balances and automatic food dispensers to mathematically calculate the predicted load size and compare with what actually happened - Shorter travel time = small load

Question 10

What is the marginal value theorem?

Answer 10

Patches do not all contain the same amount and quality of food
An optimality model that usually describes the behaviour of an optimally foraging individual in a system where resources are located in discrete patches separated by areas with no resources. Due to the resource-free space, animals must spend time traveling between patches.

Question 11

What does the marginal value theorem predict?

Answer 11

Stay on patch until marginal rate of intake = average intake rate across patches
Greater time between patches = stay longer
Generally poor quality patches = stay longer

Question 12

Give an example that illustrates the marginal value theorem?

Answer 12

Grey tits - alter the amount of food and food distance between feeders and measure the amount of time spent at each feeder and the travelling time

Question 13

Give an example of how an individual’s prey choice affects foraging?

Answer 13

Shore crab - mussel trade offs - small mussels (easily opened but little energy return ) and big mussels (long opening time and big energy return) - needs to be an intermediate optimum prey

Question 14

What was the prey choice take home message?

Answer 14

1. If large prey are abundant, eat nothing else
2. Abundance of small prey is irrelevant
3. As availability of big prey increases from a low value, the predator should make a sudden switch to eating just big prey.

Question 15

What are the three benefits of foraging in groups?

Answer 15

1. Information about where food is
2. Defence of food source
3. Predator avoidance

Question 16

What is an example of where forager groups have shared information about where food is?

Answer 16

Oyster catchers attract other oyster catchers as there is an obvious source of food

Question 17

What is an example of where forager groups have had better defence of food source?

Answer 17

Ravens in groups can better defend a carcass from another predator; naive birds follow knowledgable ones and possibly locations are advertised in soaring displays

Question 18

What is an example of where forager groups have had better predator avoidance?

Answer 18

Vigilance in pigeons and goshawks - goshawks strike rate decreased with increasing flock size because larger flocks spotted the goshawk earlier and took flight

Question 19

Why not cheat (as an individual in the group) and spend no time scanning?

Answer 19

Because once they have eaten it is safer for them as well to scan (meerkat sentinels can scan closer to the burrow as well which is also safer)

Question 20

What is an example where working in groups has increased the repertoire of prey?

Answer 20

Bottlenose dolphin - catch fish by working together and making mud nets that surround the fish; when fish try to jump over the mud, they jump straight into the dolphin’s mouth

Question 21

What is an example of a disadvantage of foraging in groups?

Answer 21

Prey startling and competition - jacks fish; while feeding in group increases the average number of prey caught but the benefits are not equally distributed - fish at the front startle prey so ones behind don’t catch as much

Question 22

What is the simplest form of resource competition?

Answer 22

Exploitation

Question 23

What is a simple model of exploitation?

Answer 23

Two adjacent habitats, one rich in food, the other poor
The two habitats will fill up as animals alternate between the two, each going where they get the best return; reward per individual: ideal free distribution

Question 24

What is ideal free distribution?

Answer 24

If animals are free to go where they do best, density of competitors should match that of the resource

Question 25

What is an example of an ideal free distribution model where competitors may be unequal (some better adapted at feeding/defending)?

Answer 25

Cottonwood aphids settles on leaf and plugs in to leaf tissue
Produces young parthenogenetically
Number of offspring is determined by how well the female feeds
Big leaves provide richest supply of sap and are occupied first.

Question 26

Where is the best place for the aphids to settle on the leaf?

Answer 26

The midrib where all the nutrients enter and leave the leaf