Main Points · 1 Main Points 1) Metabolism and allometries continued 2) Tinbergen’s Four...

1

Main Points

1) Metabolism and allometries continued

2) Tinbergen’s Four Questions

3) Optimal Foraging Theory

-- key assumptions

-- example: heritability of foraging behavior in ground squirrels

-- diet choice

-- example: dietary specialization in sea otters

-- example: CSI special mammal edition

-- when to stop eating

Terms: search time, handling time, optimal foraging theory, marginal

value theorem, patch

Pre-reading: Monday 16 October = Emlen and Oring

Wednesday 18 October = Sawyer et al 2013

Metabolism and body size

• Trade-offs between body size, metabolism, and fitness

• Small individuals/species

-- high mass-specific metabolic rates

-- fast conversion of energy into offspring,

compared to ability to obtain energy

1.8 g Etruscan shrew 2.0 g bumblebee bat

3.0 g African pygmy mouse

(right)

2

Metabolism and body size

• Trade-offs between body size, metabolism, and fitness

• Large individuals/species

-- low mass-specific metabolic rates

-- slow conversion of energy into offspring,

compared to ability to obtain energy

700 kg polar bear 1500 kg gaur

3500 kg bush elephant

3

An optimal body size?

Brown et al. 1993 4

An optimal body size?

Brown et al. 19935= smallest mammal

on landmass

= largest mammal

on landmass

An optimal body size?

Brown et al. 19936

An optimal body size?

Brown et al. 19937

8

Tinbergen’s Four Questions

Dynamic

(takes into account history)

Static

(explains only the current)

9

Tinbergen’s Four Questions

Dynamic

(takes into account history)

Static

(explains only the current)

Proximate

(how organism

functions)

Ultimate

(why organism

has evolved a

particular way)

10

Tinbergen’s Four Questions

Dynamic

(takes into account history)

Static

(explains only the current)

Proximate

(how organism

functions)

Ultimate

(why organism

has evolved a

particular way)

Mechanistic Developmental

Functional Phylogenetic

11

Tinbergen’s Four Questions

How/why do mountain lions hunt deer?

Question 1 = mechanistic answer

-- Question: how do mountain lions recognize deer as

prey?

-- Answer: deer trigger neural responses that stimulate

hunting.

12

Tinbergen’s Four Questions

How/why do mountain lions hunt deer?

Question 2 = developmental answer

-- Question: how are mountain lions able to hunt deer?

-- Answer: mountain lions learned to capture deer from

observation.

13

Tinbergen’s Four Questions

How/why do mountain lions hunt deer?

Question 3 = functional answer

-- Question: why do mountain lions hunt deer,

specifically?

-- Answer: mountain lions hunt deer to meet their

metabolic requirements.

14

Tinbergen’s Four Questions

How/why do mountain lions hunt deer?

Question 4 = phylogenetic answer

-- Question: why do mountain lions prefer to hunt deer?

-- Answer: natural selection has optimized mountain lions

to specialize on deer.

15

Basics of Foraging

16

Basics of Foraging

• Two components of foraging

17

Basics of Foraging

• Two components of foraging

-- searching/finding = search time

18

Basics of Foraging

• Two components of foraging

-- searching/finding = search time

-- subduing/pursuit/digesting = handling time

Optimal Foraging Theory

• Optimal Foraging = processes through which

animals maximize energy acquired per unit time,

energy, and risk involved in finding food.

• Key assumption: foraging behavior is transmitted

from parents to kids. Natural selection favors

animals that maximize energy gain; there are two

ways that this can occur:

-- through learning

-- through inheritance of optimally foraging

parents

19

Optimal Foraging Theory

• Test of OFT assumption:

-- calculated “optimal” diet of adult female

Columbian ground squirrels, based on plant

availability

20

Optimal Foraging Theory

• Test of OFT assumption:

-- calculated deviations between observed diets (what

squirrels actually ate) against calculations of “optimal

diets”

-- compared kids’ deviations to mom’s deviation

21

Optimal Foraging Theory

Mom’s deviation from prediction

Kid

’s d

evia

tio

n f

rom

pre

dic

tio

n

Ritchie. 1987.22

Optimal Foraging Theory

Mom’s deviation from prediction

Kid

’s d

evia

tio

n f

rom

pre

dic

tio

n

Ritchie. 1987.23

Optimal Foraging Theory

Mom’s deviation from prediction

Kid

’s d

evia

tio

n f

rom

pre

dic

tio

n

Ritchie. 1987.24

Optimal Foraging Theory

Mom’s deviation from prediction

Kid

’s d

evia

tio

n f

rom

pre

dic

tio

n

• Discussion Q: From the graph below, what can we

conclude about if and how foraging behavior is

transferred from mom to kids?

Hint: think in terms of

learning versus

inheritance.

If foraging behavior were

entirely learned (or entirely

inherited), would these

graphs look different?

How?

Ritchie. 1987.25

26

Optimal Foraging Theory

• Two decisions required of optimal foragers

27

Optimal Foraging Theory

• Two decisions required of optimal foragers

1. what do I include in my diet?

2. when do I leave a “patch”?

28

Diet Choice

• What do I include in my diet? Should depend on:

-- ease of searching (finding) and handling

(subduing/pursuing/digesting)

29

Diet Choice—Reintroduced Sea Otters

site 1 site 2 Tinker et al. 2008.

ott

er

den

sit

yp

rey d

en

sit

yfo

od

in

take

-- site 1 = sea otters close

to carrying capacity;

resources limiting

-- site 2 = sea otters

recently reintroduced;

resources abundant

30

Diet Choice—Reintroduced Sea Otters

site 1 site 2 Tinker et al. 2008.

ott

er

den

sit

yp

rey d

en

sit

yfo

od

in

take

-- site 1 = sea otters close

to carrying capacity;

resources limiting

-- site 2 = sea otters

recently reintroduced;

resources abundant

31

Diet Choice—Reintroduced Sea Otters

site 1 site 2 Tinker et al. 2008.

ott

er

den

sit

yp

rey d

en

sit

yfo

od

in

take

-- site 1 = sea otters close

to carrying capacity;

resources limiting

-- site 2 = sea otters

recently reintroduced;

resources abundant

32

Diet Choice—Reintroduced Sea Otters

site 1 site 2

site 1 site 2

site 1 site 2

Tinker et al. 2008.site 1 site 2

ott

er

den

sit

yp

rey d

en

sit

yfo

od

in

take

33

Diet Choice

• What do I include in my diet? Should depend on:

-- ease of searching (finding) and handling

(subduing/pursuing/digesting) prey

-- forager’s state (i.e. how desperate am I)?

34

Diet Choice—the Man-Eaters of Tsavo

• In 1898, between 30-135 humans killed by lions in

southern Kenya while constructing Kenya-Uganda

railway.

35

Diet Choice—the Man-Eaters of Tsavo

• Both individuals were shot and donated to

Chicago Field Museum in 1898, where they

currently are on display.

36Yeakel et al. 2009.

Diet Choice—the Man-Eaters of Tsavo

37Yeakel et al. 2009.

Diet Choice—the Man-Eaters of Tsavo

Lion bone

Lion hair

38Yeakel et al. 2009.

Diet Choice—the Man-Eaters of Tsavo

Taita (human) bone

Taita (human) hair

39

Optimal Foraging Theory

• Two decisions required of optimal foragers

1. what do I include in my diet?

2. when do I leave a “patch”?

Optimal Foraging Theory

• Marginal Value Theorem =

an animal should remain in a patch until the energy

gain from that patch has declined to the average

gain for the habitat.

40

The Marginal Value Theorem

• What is a patch?

41