4: Optimal foraging Flashcards
why can we make precise predictions on behaviour?
behavioural ecology has strong theory
what is the optimality logic?
selection will favour animals that forage most effectively
what is optimality modeling used for? (3)
- used to determine the best course of action for an animal
- insights into optimal foraging (often graphically)
- predict how and animal should optimise its own food intake or food provisioning to young per unit time
what ideas did John Maynard Smith introduce?
ideas from economic theory and applied these models to animal behaviour
- developed optimality modelling
in a Zach study 1979 what was the study and what were the observations ? (3)
whelk choice by North western crows in USA
- always select large whelks (3.5-4.4cm)
- drop them from 5m onto rocks to break them open and eat body inside the shell
- keep dropping the same whelk until it breaks
in a Zach study 1979 what were the predictions? (3)
- large whelks should break easier at 5m than small whelks
- whelks dropped at <5m should be less likely to break but if >5m no more likely to break
- chances of whelk breaking should be independent of number of times its dropped - each time its dropped it has the same chance of breaking
in a Zach study 1979 after dropping whelks from a tower on the beach from different heights what were the results found? (6)
- large whelks take fewer drops to crack (5 compared to 18 for small)
- larger whelks have more calories
- 5m is the optimal height with 5.6 being the min energy expenditure
- if drop from too high then whelk may be stolen before reaching it
- chance of whelk breaking not affected by number of previous drops
- optimal behaviour by dropping from 5m and using the same whelk until it breaks
what can a hypothesis based on cost benefit logic that is incorrect lead to?
further insights
why may a hypothesis based on cost benefit logic be incorrect? (4)
- animal may not have been well designed by selection (not yet evolved to changing environment)
- observations may have been inappropriate so need to re-assess experimental design
- important factor may have been omitted from the model
- assumptions may not have been valid for the species studying
describe the predictions of the oystercatcher study on constraints on foraging
predicted to select large mussels that yield the most food
what were the results of the oystercatcher study on constraints on foraging
- birds selected mussels smaller than predicted as cant open the largest ones
- if only mussels that can be opened are considered then the optimum size is 50mm which matches observations
what do moose need to eat and why must they carefully select what they eat?
energy rich low sodium deciduous forest leaves or sodium rich low energy aquatic vegetation surrounding lakes
- plants may be deficient in nutrients
in the moose what can set a limit on the total food it can process daily?
stomach space- rumen constraint
In Belovsky 1978 optimal foraging approach on moose what was found? (5)
- energy gained from either lots of aquatic vegetation or a little terrestrial
- cant just exist on aquatic plants
- only a small area satisfies all constraints
- constraints include energy, sodium and rumen
- diet lies trying to maximise energy intake
what is the general economic model also known as?
- what does it predict?
Charnovs marginal value theorem
- how animals should forage in a patchy environment
what do foraging environments tend to be?
patchy with food disturbed in clumps
what are 2 examples of a patchy foraging environment?
- hummingbirds move from bush to bush to collect food
- swarm of krill is a patch for humpback whales
what is the loading curve in MVT?
- diminishing returns of continuing to feed in a patch
- rate of food intake decreases over time as the patch may become depleted or the animal overloaded with food
what is the optimal patch time in MVT and how does it vary?
- if didn’t take long to reach the patch there will be a steeper tangent to the curve
- longer travel time means animal should spend longer in the patch to maximise energy intake
what happens if an animal leaves a patch before or after its optimal time?
the rate of energy intake is lower
if you plot travel time against time spent in a patch what is the curve?
curve of diminishing return
what are the 4 main assumptions of the MVT?
- travel time between patches is known (unless searching fo next flower in a sparse patch)
- travel costs = patch costs (true for hovering hummingbird but not seed eater )
- patch profitability is known
- no predation
what did Kacelnik discover in 1984 about what starlings get as they forage and why?
diminishing returns
as harder to find food when carrying prey
- more it carries the less efficient it is at probing for more
what did Kacelnik discover in 1984 about what starlings feed on and how does their optimum prey number to collect differ between taking a long or shorter travel time?
leatherjackets- daddy longlegs larvae
- longer = 7 prey
- shorter = 4/5
what was Kacelnik 1984 set up for starlings?
trained to feed from mealworms from artificial patches with diminishing returns placed at 8-600m from nest
- dropped mealworms successively slower to create diminishing returns
what did Kacelnik discover in 1984 for how the starling load size changed in the experiment?
increased with increasing distance from the nest
Cowie 1977 tested the MVT assumptions using great tits- what was done/found? (5)
- expend more energy during travel time 30 patches with 5 experimental trees
- different spacing of trees varied travel time between patches
- travel and foraging times closer than predicted by the model
- differences in travel/patch costs influence foraging behaviour
what was the Lima 1984 study on Downy woodpeckers to test MVT assumptions? (8)
- trained them to forage for seeds from logs each with 24 holes
- logs were either empty or with seeds
- birds sample different patches to work out profitability
- 0 or 24 seeds 1.7 looks
- 0 or 6 seeds 6.3 looks
- 0 or 12 seeds 3.5 looks
- observed means close to predicted
- used information during foraging to maximise energy intake and minimise search costs
what do optimality models used to study behaviour provide?
testable quantitative predictions
- so can test theories of an animal’s behaviour
what do optimality models and behaviour involve?
explicit assumptions - can alter model to learn more about subtle behavioural differences
what do optimality models and behaviour illustrate?
the generality of decision making - can be applied to different species and not just based on foraging behaviour (e.g. how many eggs should be laid)
what are the 3 responses when a model fails to predict observations?
- ignore it and count as error
- accept animal is sub optimal
- rebuild model
how is the rate at which an animal gains energy quantified?
dividing caloric value by time taken to find food
how may leafcutter ants appear to be acting non-optimally?
reduced daytime foraging by larger ants due to attacks from parasitic flies
