Optimal Foraging Flashcards
What are the two perspectives of optimal foraging?
Individual and group
Why is optimal foraging such an important aspect of behaviour?
Energy - need a positive energy balance where input exceeds output
What are some energy inputs?
Feeding
What are some energy outputs?
Homeothermy Homeostasis Resource defence Sex Rearing offspring
How do animals minimise energy output?
Feeding efficiently through optimal foraging
Which two factors may affect individual economic decisions?
Food quality (size, nutrition, number) Time (searching, handling, commuting)
What is an example of when an animal has had to make economical decisions?
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
What two things do the optimum number of prey depend upon?
Search time and commuting time
How was the hypothesis “change in commuting distance changed the optimum number of prey” tested?
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
What is the marginal value theorem?
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.
What does the marginal value theorem predict?
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
Give an example that illustrates the marginal value theorem?
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
Give an example of how an individual’s prey choice affects foraging?
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
What was the prey choice take home message?
- If large prey are abundant, eat nothing else
- Abundance of small prey is irrelevant
- As availability of big prey increases from a low value, the predator should make a sudden switch to eating just big prey.
What are the three benefits of foraging in groups?
- Information about where food is
- Defence of food source
- Predator avoidance
What is an example of where forager groups have shared information about where food is?
Oyster catchers attract other oyster catchers as there is an obvious source of food
What is an example of where forager groups have had better defence of food source?
Ravens in groups can better defend a carcass from another predator; naive birds follow knowledgable ones and possibly locations are advertised in soaring displays
What is an example of where forager groups have had better predator avoidance?
Vigilance in pigeons and goshawks - goshawks strike rate decreased with increasing flock size because larger flocks spotted the goshawk earlier and took flight
Why not cheat (as an individual in the group) and spend no time scanning?
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)
What is an example where working in groups has increased the repertoire of prey?
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
What is an example of a disadvantage of foraging in groups?
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
What is the simplest form of resource competition?
Exploitation
What is a simple model of exploitation?
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
What is ideal free distribution?
If animals are free to go where they do best, density of competitors should match that of the resource
What is an example of an ideal free distribution model where competitors may be unequal (some better adapted at feeding/defending)?
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.
Where is the best place for the aphids to settle on the leaf?
The midrib where all the nutrients enter and leave the leaf
