Finding food

Question 1

why forage?

Answer 1

basic requirement for life
- cell metabolism

improve body quality
- status ornaments

feed breeding partner

feed offspring

Question 2

economics of foraging

Answer 2

maximise profits and minimise loss

Question 3

time budget equation

Answer 3

time budget

= searching time + handling time

Question 4

handling time equation

Answer 4

handling time
= no. of prey taken in time T
x time spent handling 1 prey item

Question 5

number of prey taken in time T equation

Answer 5

number taken
= area searched
x prey density
x time searching

Question 6

searching time equation

Answer 6

searching time
= number of prey taken in time T/
(area searched x prey density)

Question 7

complex time budget equation

Answer 7

time budget

= (Ha/ a H) + (Ha*Th)

Question 8

assumptions of budget time equation

Answer 8

all animals are identical
- same handling time

no variation in any of the parameters in space/time

no interactions between animals
- no prey excluding others

Question 9

how is the environment patchy?

Answer 9

vary in:

food density

predator no.s

size + type of prey
- may exclude each other

Question 10

how many items should a parent collect?

• best type of foraging
• too few
• too many

Answer 10

= optimal foraging

wasted time + energy on flying to food patch
-> not delivering much profit

lose prey items whilst foraging
+ increased risk of predation

Question 11

marginal value theorem (MVT)

Answer 11

considers economic costs of altering the value of another factor (e.g. energy costs)

Question 12

MVT in animal behaviour

- 3 axes on graph

Answer 12

loading curve
= no. of items taken to offspring

searching time
= time spent in food patch

travel time
= time spent between nest + food patch

Question 13

MVT in animal behaviour

• optimal searching time
• longer travelling time means…?
• longer searching time means…?

Answer 13

time that delivers highest profit at lowest travelling time

more time spent gaining nothing

results in some gain
-> gain increases with searching time

Question 14

marginal value equation in animals

Answer 14

marginal value
= food intake/
(travel time + searching time)

Question 15

how can the optimum time be altered?

Answer 15

change travel time
- longer travel time means longer optimum searching time + need to take more prey

change shape of gain curve

Question 16

when will optimal foragers spend longer in a patch of resources?

Answer 16

more profitable patches

as distance between patches increases

when whole environment in less profitable

Question 17

optimality models

• similar to
• key components

Answer 17

quantitative economic cost/benefit analyses

>constraints
>behavioural options
>'currency' 
- may be maximised e.g. food intake 
- may be minimised e.g. risk of predation

Question 18

optimality models

- pros

Answer 18

make testable + quantitative predictions

use explicit assumptions

general
- may be applicable to different organisms + behavioural situations

Question 19

optimality models

- cons

Answer 19

selection of constraints, behavioural options + ‘currencies’ may be incomplete/ hard to quantify
- e.g. predation risk often uses surrogate measures

if observed behaviour different to expected, how can discrepancy be explained?
- wrong model
OR
- animals behave non-optimally?

-> come up with new model with new constraint + hypothesis

Question 20

testing support for competing hypotheses

e. g. bird + mussels
- hypotheses

Answer 20

predicted:
prey on big mussels as most profitable

observed:
not many big mussels were taken

so rejected hypothesis

Question 21

testing support for competing hypotheses

e. g. bird + mussels
- what happened next?

Answer 21

made additional observations:

large mussels potentially excluded as too big + hard to open (encrusted with barnacles)

Question 22

trade off between starvation and predation

Answer 22

animals need to feed BUT also avoid being eaten

Question 23

trade off between starvation and predation

e.g. prey selection in 3-spined sticklebacks

Answer 23

presence of predator:
fish attack prey less frequently even if high prey density

2 competing factors from fish POV:
> probability of seeing prey again
> if they make an attack on prey, predator will see and eat them

Question 24

trade off between starvation and predation

e. g. body mass in birds
- benefits of energy reserves

Answer 24

fuel for foraging breaks

buffer against unfavourable foraging conditions

insulate body from environment

Question 25

trade off between starvation and predation

e. g. body mass in birds
- costs of energy reserves

Answer 25

acquisition
(time, energy, risk of injury)

maintenance (mass-dependent costs)

metabolic expenditure

pathological conditions
e.g. pulmonary stress

decreases locomotor performance

• > fly slower + less agile
• > increases predation risk

Question 26

trade off between starvation and predation

e. g. body mass in birds
- study of small passerine birds + sparrow hawks

Answer 26

absent hawks
= high body mass of small birds

increasing hawks
= decreasing body mass

established hawks
= low body mass

Question 27

how can we combine the various measures of performance into one?

what does this link?

Answer 27

reproductive success
= fitness
e.g. no. of offspring produced over life-time

foraging behaviour
predation risk
mating success
reproduction