Optimal Foraging Ecology and Diet Choice

-- The need to acquire energy to maintain homeostasis is a universal property of life

-- Natural selection

We expect to see adaptive behaviors that permit individuals to efficiently and effectively acquire and utilize energy

Foraging under predation risk – there is a fundamental tradeoff between acquiring energy and avoiding predation

Red KnotCalidris canutus

Tidal mudflat foragers

Ruddy turnstoneArenaria interpres

Inshore foragers

Differences in predator escape?

• Knots – advanced warning and collective flight maneuvers• Turnstones – little warning, find cover, every turnstone for itself

At the Netherlands Institute for Sea Researchthe animal caretaker kept track of knots’ abilitiesto make 90 degree turns into the aviary…..

> 160 g, knots compromise their flight abilities

Flight performance increases with an increase in the ratio of:

Pectoral Muscle Mass/Body Mass

So how do you increase flightperformance?

Body Building to defy death

Red-eyed tree frog Agalychnis callidryas

http://sites.bu.edu/warkentinlab/video-library/

Rain and snake have differentvibrational signatures

Signal Detection Theory (see Box 42, p111 in your textbook)

Patchiness&

The Ecology of FEAR

Quitting Harvest Rates&

Giving-up Densities (GUDs)

0

10

20

30

Foo

d le

ft be

hind

15 10 20 10 30 10

No significant differences

Prediction #1 – Differences in initial patch quality will not influence the giving-up rule, i.e., at a constant quitting harvest rate

It is a “No Regrets Strategy”

0

1

2

3

Foo

d le

ft be

hind

underbush

in theopen

vipers

owls

lights

vipers &lights

0

100

200

Qui

tting

har

vest

rat

e

300

400

500

Aug July

openbush

Dec - Aprrattlesnakes hibernating

Prediction #2 – Increases in individual foraging costs will result in higher quitting harvest rate

Prediction #3 – As the value of energy decreases organisms should be less willing to exposed themselves to risk

Exchange rate of survivorship and energy

Exchange rate of time and energy

QHR = P + MOC + C ____ F e

Harvestrate

Predationcost

Missed opportunity

cost

Metabolic cost

P F e

Hazardous Duty Pay

0

2

4

6

Foo

d le

ft be

hind

safe saferisky risky

10

10

Forest edge

10

10

10m

50m add 50g ofsunflowers

seeds

Perceived risk of predation Survivor’s Fitness

The value of energy/foodi.e., marginal fitnessgain from foraging

The Fear Equation (Joel Brown)

Signaler Receiver (‘intended’)

(sender) (recipient)

INFO

INFO

Recipient - Eavesdropper

Alarm calls and Eavesdropping

Bushbuck

Grey duiker

QHR = P + MOC + C ____ F e

Harvestrate

Predationcost

Missed opportunity

cost

Metabolic cost

P F e

Hazardous Duty Pay

Islands of Fertility

500

435

371

300

Bushbuckbark

Silent

Rank

Giv

ing-

up d

ensi

ty

Proportion of time vigilant

Mean durationof scan (sec)

COGNITIONHow should squirrels change their behavior

in the perceived presence of a cache robber?

- False-caches- Cache less often - Cache in remote/hidden locations- Frequent recaching

**Reduce the Future Value of food

Squirrels devalue cacheable food in the perceived presence of jays (i.e., reduce the future value of cacheable food)

Cacheable NutsFuture Value

(cached 54 of 55)*

Non-cacheable NutsNo Future Value

(ate 52 of 55)*

* Kotler et al. 1999

Food spoils and ripens….hence, a food that stores well has higher future value

Detecting changes in Future Value

QHR = P + MOC + C __Fe

____ F e

F e

will result in QHR or GUD

Compare GUDs on cacheable food With and Without the perceived presence of jays while holding GUD on non-cacheable food fixed(i.e., compared to a fixed currency)

P = predation costMOC = missed opportunity costC = metabolic costQHR = quitting harvest rate F/e = marginal value of energy

~75m

~100m station of two trays

Speaker (jay or winter birds)

~25m

Cachable food= hazelnuts in the shell

Non-cachable food= hazelnuts with shell

removed

~75m

~100m ~25m

Jay Near Jay FarCONTROL

GUD (# cachable nuts remaining)

3

5

7

9

Control

Blue jay

Away Near

• Squirrels devalue cacheable food in the perceived presence of jays

Results