OPTIMAL FORAGING

Question 1

How do animals maximise their fitness?

Foraging

Answer 1

• Foraging as efficiently as possible.
• Animals should balance the benefits (calorie intake) against the cost (time / energy expended) to maximise food intake per unit time.

Question 2

What did John Maynard Smith introduce into animal behaviour?

Answer 2

Economic theory

Question 3

How did Zach test foraging behaviours of notherwestern crows in 1979?

Answer 3

• Whelk Foraging
• Tested by dropping whelks from different heights
• 5 - 5.6 metres - best height to drop whelk (dropping times and energy expenditure)
• Crows choose large whelks, drop from 5m and stuck with the whelk until it broke
• Crows choose optimal sized whelks and drop them from a optimal height

Question 4

When a hypothesis based on cost benefit logic is found to be incorrect this can lead to further insights. What are these?

Answer 4

1. The animal may not have been well ‘designed’ by selection
2. The observations may have been inappropriate
3. An important factor may have been omitted from the model
4. The assumptions may not have been valid for the species being studied

Question 5

How are oystercatchers an example of a mismatched study?

Answer 5

Study found that oystercatchers were feeding on smaller mussels than prediction by optimal foraging.

Question 6

Why was the oystercatcher study mismatched?

Answer 6

• Was later found that large mussels couldn’t be opened by the oystercatchers.
• Taking this into consideration the new prediction is closer to reality when only considering mussels that can be opened.

Question 7

How does nutrient intake constrin moose foraging?

Answer 7

Moose need to eat aquatic vegetation rich in sodium and/or energy rich forest leaves.
There is also the effect of satiation

Question 8

What are the competing constraints on optimal foraging a moose faces?

Answer 8

• Energy constraint
• Sodium constraint
• Rumen constraint

Question 8

Outcome of study on moose optimal foraging

Answer 8

• Belovsky plotted a graph showing the optimal foraging of moose within the constraints (energy, sodium & rumen).
• Found that moose were within the triangle of optimal foragin
• Moose maximise their energy output over sodium intake.

Question 9

What does the Charnov’s marginal value theorem test?

Answer 9

• Time spent foraging optimally
• Patchy foraging environments

Question 10

Charnov’s marginal value theorem

Answer 10

• Foraging environments tend to be patchy
• Loading curve - curve of diminishing returns
• Longer the travel time = longer the animal should spend at the foraging site to optimise life/energy.

Question 11

Optimal foraging: Starlings collecting leather jackets (theory)

Answer 11

Starlings get diminishing returns as they forage because it is harder to find food when

Question 12

Hoe was the optimal foraging time of Starlings collecting leather jackets tested?

Answer 12

• Kacelnik (1984)
• Starlings were trained to eat mealworms from a tray.
• Generated loading curve by dropping mealworms onto a tray more slowly each time.
• Simulated diminishing returns
• Altered distance of tray from nest.

Question 13

Results from optimal foraging in starling study

Answer 13

• Load size increases with increased distance from the nest
• Close correspondence between predicted and observed load size

Question 14

What are the restrictive assumptions of the marginal value theory?

Answer 14

• Travel time between patches is known
• Travel costs = patch cost
• Patch profitability is known
• No predation

Etc…..

If assumptions are violated model needs to be altered to take these into consideration

Question 15

Testing assumptions: Cowie tested travel time / patch costs. What did he show?

Do travel costs = patch costs?

Answer 15

• That identifying a mismatch between orginal and observed data Cowie showed that differences in trabel and patch costs affects an individuals foraging behaviour.
• By adjusting the model to take that into account, the fit was closer.

Question 16

Is patch profitability known? Woodpecker study

Lima 1984

Answer 16

• Foraging logs with 24 holes - empty or with seeds.
• Woodpeckers used information gained during foraging to maximise net energy gain

Question 17

What do Optimality models and behaviour show?

Answer 17

1. They provide testable quantitative predictions
2. They involve explicit assumptions
3. They illustrate the generality of decision making

Question 18

What to do when the model fails to predict observations?

Answer 18

1. Ignore it (count as acceptable error) (cop out)
2. Accept animal is sub-optimal (cop out)
3. Re-build model (best option)