Behavioural Economics Flashcards
Natural selection is..
iterative and competitive, producing behavioural phenotypes that represent the best achievable balance of costs and benefits.
Individuals are expected to evolve to behave optimally (within the bounds of ontogenetic constraints).
trade offs -
Individuals exhibiting sub-optimal cost-benefit balances (trade-offs) will leave fewer offspring.
All behavior…
…takes time which cannot then be allocated to other activities
…costs energy which cannot then be allocated to other activities
- If animals do try to carry out two types of behaviour at once, efficiency in both is lost
e. g. foraging / keeping watch for predators - The benefits of any behaviour are context-dependent = show temporal variation (daily, tidal, oestral, seasonal or developmental)
Optimality modelling in Behavioural Ecology -
- is based on cost-benefit analysis.
- makes quantitative predictions about behaviour.
- seeks to identify what trade-off between costs and benefits of a behaviour will maximise net fitness.
- uses models to generate testable hypotheses.
minimizing energy expenditure - Crow foraging strategies:
Crows in coastal areas feed on shellfish (whelks) - Whelks dropped onto rocks from height - to crack open
- How high should a crow fly up before dropping whelks? - flying uses energy that crow is trying to get from food
- Take off and vertical flight is very costly for birds
- experiments observed that crows open whelks using the minimum energy possible and drops are made after crow turns downwards to see where whelk lands
The functional approach:
- Comparing actions in terms of their contribution to future reproductive success
= hard to assess (tracking offspring of offspring…)➔ instead rely on simpler ‘currencies’
e. g.
- Net rate of energetic gain: 𝛾 (gamma)
- Foraging efficiency: 𝐸∕ℎ= (energy gained 𝐸 / handling time ℎ)
Net rate of energetic gain: 𝛾 (gamma)
Maximising 𝛾 means:
- maximising the amount of energy gained per unit time spent foraging; same as…
- minimising the time required to obtain a given amount of energy.
e. g. kestrel foraging -
- In summer, prey is more frequent…so perch hunting has higher gain rate
- In winter, flight hunting is by far the more common strategy…but perch-hunting still occurs depending on other constraints
𝛾 (net gain rate) =
energetic gain rate - energetic expenditure rate
prey size constraints -
- Larger food items contain more energy…
…but they may also take longer to catch and eat
𝐸∕ℎ= energy gained / handling time = Profitability
Prey size selection in redshanks:
- redshanks feed on ragworms - a range of sizes are always available… however sometimes birds only feed o n large worms, sometimes birds feed on large and small worms
Field observations suggested that small worms were rejected when large worms were common, but taken when large worms were rare.
➔ Experiments manipulating the encounter rate with large and small worms +
knowing their relative 𝑬∕𝒉 profitability predicts the point at which redshanks started taking small worms.
- large prey should always be eaten
- Small prey should be eaten provided that: Gain from eating small prey exceeds the gain from rejection and searching for a more profitable large prey item
including less profitable items in the diet depends solely on…
time spent searching - i.e., the abundance of the more profitable prey
A model of choice between large and small prey can be made if we know…
- the energy content of the two types of prey items
- their associated handling times and
- the time taken to search for the more profitable prey
Predictions of the model: deciding prey size
- The predator should either:
Specialise solely on prey type 1 (more profitable prey) OR
Eat both prey type 1 and prey type 2 (less profitable prey) as the are encountered
but it should not specialise on prey type 2 - The decision to specialise on type 1 prey depends on the time taken to search for the more profitable prey
- The switch from specialising solely on prey type 1 to generalising (eating both prey sizes as encountered) should be sudden, as the commonness of the best prey decreases: ➔ there should be no partial preferences.
A test of the prey choice model with great tits:
- Great tits offered large and small mealworms and a conveyor belt system controls encounter rates.
- Large mealworms contained twice the energy than small ones (𝐸1/𝐸2 =2)
- Encounter rate with large worms was changed throughout the experiment to span the predicted switch-point
- predicted to specialize on large worms
- observed not exactly same as expected because - Prediction assumes birds have perfect information
…but they are just guessing the abundances
Marginal Value Theorem: Maximising rate of food transfer -
Model used to determine how long individuals should persevere when experiencing diminishing returns for their efforts with increased time
e.g. Birds provisioning chicks are limited by the amount of food they can carry in their beaks.
The rate at which they can fill up their beaks decreases as the beak fills up.
Costs and benefits of small and large load sizes.
Assume starlings are efficient parents = maximise rate of prey transfer to nest =𝑓𝑜𝑜𝑑∕𝑡𝑖𝑚𝑒.
- also considers travel time back to nest and patch density
