Lecture 4 - optimal foraging Flashcards
why does natural selection favour animals that behave most efficiently?
because for example individuals that forage optimally will maximise energy intake while minimising handling time
who pioneered optimality modelling and what is it used for?
john maynard-smith
- used to determine how animals can best optimise (best source of action) their behaviour
what is optimality logic?
- selection will favour animals that forage most efficiently
how can you quantify the rate at which an animal obtains energy?
divide the caloric value by the time to find, process (e.g. open a mussel) and eat something
How do Northwestern crows predate whelks ?
- they drip the whelks from 5m onto rocks to crack them open
- small whelks are unprofitable so they only select large ones
- they continue to drop the whelk until it breaks
what gives an insight into the strategy of the northwestern crows?
measurements of drop height on the number of drops needed to crack whelks of different sizes
what were the 3 predictions of the northwestern crow experiment?
1) large whelks should break more easily at 5m than small whelks
2) whelks dropped at <5m should be less likely to break, whelks dropped at >5m should be more likely to berak
3) the chances of a whelk breaking should be independent of number of times its dropped
what were the results of the experiment on northwestern crows whelk strategy?
1) bigger whelks require fewer drops to crack
2) dropping from 5m is almost as good as greater heights
3) there doesnt seem to be any resistant whelks so if a whelk has not cracked after say 5 drops it is probably just lucky so its not appropriate to abandon whelks that do not crack
describe mismatch?
When a hypothesis based on cost benefit logic is found to be incorrect this can lead to further insights
what are the 4 further insights from mismatch
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
predictions can be made about the optimal size of food items that should be taken by an animal however its not always the case - give an example of this
oystercatchers were found to not select the largest mussels (appear to be behaving non-optimally) - optimum size for mussels that can be opened is 50mm- the larger mussels were more difficult to open
describe the mismatch foraging of leaf cutter ants?
- the larger ants reduced their daytime foraging to limit attacks from parasitic flies
describe the diet of moose
moose need to eat energy rich forest leaves and sodium rich aquatic vegetation
moose behave optimally in the bounds of 3 constraints what are they?
1) an energy constraint
2) sodium constraint
3) a rumen constraint
- that means they dont eat the highest/ expected for each food source because they have to have a balance between the 3 constraints
what is charnovs marginal value theorem
- foraging environments tend to be patchy
- when foraging animals need to decide when to move from one patch to another - the theorem predicts how animals should forage in a patchy environment
what is the idea charnovs marginal value theorem is based on?
the idea that animals should move from one patch to the next (or return to their young with food) when the patch at which they are feeding becomes unprofitable - depends on the quality of the patch and the time taken to travel between patches (or to and form their young)
on the marginal theorem graph what does the loading curve show?
the diminishing returns of continuing to feed on a patch
what does the tangent to the loading curve show?
indicates the optimal time for an individual to forage in th§e patch
what does increasing travel time predict?
that an individual should spend longer in the patch
describe Kacelnik (1984) experiment on starlings?
- Starlings get diminishing returns as they forage because it is harder to find food when carrying prey.
- Starlings trained to feed from artificial patches with diminishing returns placed at 8m - 600m from nest
- experiments found that he starlings forage optimally when collecting food for their young
the MVT is restrictive, describe 4 assumptions of it
1) travel time between patches is known
2) travel time and patch time have equal energetic costs
3) patch profitability is known
4) no predation or competition etc
describe an experiment teting the assumption do travel costs= patch costs?
- great tits (Cowie 1997)
- great tits expend more energy during travelling time than during patch time
- cowie adjusted for this and then observed travel and foraging times that were closer to those predicted by the model
describe the experiment testing the assumption ‘patch profitability is known’
Lima (1984) - Downy woodpecker - when faced with patches of unknown profitability they sampled the patches and are thereby able to maximise their energy intake by minimising their search costs
why are optimality models good for studying behaviour?
1) they provide testable quantitative predictions that can be used to test whether our theories for why animals are behaving in particular ways are correct
2) they involve explicit assumptions -
3) they illustrate the generality of decision making
things to do when the model fails to predict observations?
1) Ignore it (count as acceptable error)
2) Accept animal is sub-optimal
3) Re-build model
when animals dont behave in the way the models predict we can rebuild our models to incorporate constraints or alter assumptions and thereby learn more about the behaviour
