OPTIMAL FORAGING Flashcards
How do animals maximise their fitness?
Foraging
- 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.
What did John Maynard Smith introduce into animal behaviour?
Economic theory
How did Zach test foraging behaviours of notherwestern crows in 1979?
- 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
When a hypothesis based on cost benefit logic is found to be incorrect this can lead to further insights. What are these?
- The animal may not have been well ‘designed’ by selection
- The observations may have been inappropriate
- An important factor may have been omitted from the model
- The assumptions may not have been valid for the species being studied
How are oystercatchers an example of a mismatched study?
Study found that oystercatchers were feeding on smaller mussels than prediction by optimal foraging.
Why was the oystercatcher study mismatched?
- 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.
How does nutrient intake constrin moose foraging?
Moose need to eat aquatic vegetation rich in sodium and/or energy rich forest leaves.
There is also the effect of satiation
What are the competing constraints on optimal foraging a moose faces?
- Energy constraint
- Sodium constraint
- Rumen constraint
Outcome of study on moose optimal foraging
- 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.
What does the Charnov’s marginal value theorem test?
- Time spent foraging optimally
- Patchy foraging environments
Charnov’s marginal value theorem
- 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.
Optimal foraging: Starlings collecting leather jackets (theory)
Starlings get diminishing returns as they forage because it is harder to find food when
Hoe was the optimal foraging time of Starlings collecting leather jackets tested?
- 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.
Results from optimal foraging in starling study
- Load size increases with increased distance from the nest
- Close correspondence between predicted and observed load size
What are the restrictive assumptions of the marginal value theory?
- 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
