Lecture 4: Optimal Foraging

Question 1

optimal foraging is a balance between the

Answer 1

costs and benefits in question

–benefits of calorific intake and cost of time and costs it has getting it

Question 2

optimality logic =

Answer 2

selection will favour animals that forage most efficiently

Question 3

optimality modelling is used to

Answer 3

determines the best course of action for an animal e.g. maximising food intake or offspring provisioning rate per unit time

Question 4

john maynard smith linked to

Answer 4

optimality modelling, brought economic idea of costs and benefits

Question 5

Whelk Choice by Northwestern Crows OBSERVATIONS by Zach 1979

Answer 5

• Crows always chose large whelks (3.5-4.4cm)
• drop them from about 5cm onto rocks to break them open
• they keep dropping a whelk until it breaks

Question 6

Whelk Choice by Northwestern Crows PREDICTIONS by Zach 1979

Answer 6

• large whelks should break more easily at 5m than small
• whelks dropped at <5m should be less likely to drop, dropped at >5m should not be more likely
• chance of whelk breaking should be independent of the number of times its dropped

Question 7

Whelk Choice by Northwestern Crows EXPERIMENT by Zach 1979

Answer 7

Drop whelks from tower on beach

Question 8

Whelk Choice by Northwestern Crows EXP RESULTS by Zach 1979

Answer 8

• large whelks broke more easily at 5m
• took around 4/5 drops, way less than smaller
• 5m optimum drop height
• found drops and breaking to be independent

Question 9

When a hypothesis based on cost benefit logic is found to be incorrect this can lead to further insights.

Answer 9

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

Question 10

Oyster catchers mistaken study, found that oyster catchers were choosing mussels smaller than predicted BECAUSE

Answer 10

large mussels were impossible to open (model A and model B)

Question 11

Moose Belovsky 1978: foraging is strongly affected by

Answer 11

• ->Sodium requirements
• moose feed in two habitats, deciduous forest (high energy, low sodium), lakes (high sodium, low energy)
• graph plotting both areas to determine optimal model (energy constraint, rumen constraint, sodium constraint) –> trying to gain as much energy with just eating enough sodium

Question 12

nutrient quality of food is often more important for __ than ___

Answer 12

herbivores rather than carnivores (as must ensure they’re getting enough nutrients, e.g. Moose)

Question 13

Charnov:

Answer 13

Marginal Value Theorem

• animals feeding in patchy environments (when to move from one patch to another)
• tangent to loading curve = optimal time to leave

Question 14

foraging environments tend to be

Answer 14

patchy

Question 15

when animal arrives at patch of food

Answer 15

• has high food quality
• loading curve (arc ^ ending upwards)
• -when do they give up on this patch and move onto next?

Question 16

consequences of animal leaving patch too early/late

Answer 16

• too early: waisting time travelling (miss out on food)

- too late: waisting time at patch

Question 17

Charnel’s Marginal value theorem: if travel time between patches varies then we’d expect

Answer 17

different optimal time spent at patch (due to different tangent)

Question 18

loading curve =

Answer 18

line of diminishing returns

Question 19

optimal foraging: Starlings

-Kacelnik 1984

Answer 19

• prey leather jackets to feed chicks

- starlings get diminishing returns as they forage because it is harder to find food (probe) when carrying prey

Question 20

Kacelnik 1984 starlings experiment

Answer 20

• trained starlings to feed from artificial patches with diminishing returns placed at 8-600m from nest
• RESULTS: load size increased with distance from nest

Question 21

Assumptions of Marvel value theorem

Answer 21

• travel time between patches is known
• travel costs = patch costs
• patch profitability is known
• no predation

Question 22

MVT assumption: to travel costs = patch costs COWIE 1977

Answer 22

Great tits, experimental trees

–> expend more energy during travelling time than during patch time.

Question 23

MVT assumption: Is patch profitability known? LIMA 1984

Answer 23

Downy Woodpecker: trained to forage from logs each with 24 holes -empty or with seeds
–pretty close findings

Question 24

optimality models and behaviour entail:

Answer 24

• they provide testable quantitive predictions
• they involve explicit assumptions
• they illustrate the generality of decision making

Question 25

What to do when the optimality model fails to predict observations?

Answer 25

• Ignore it (count as acceptable error)
• Accept animal is sub-optimal
• Re-build model