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
Transcript
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)
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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
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Tinbergen’s Four Questions
Dynamic
(takes into account history)
Static
(explains only the current)
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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)
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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
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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.
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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.
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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.
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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.
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Basics of Foraging
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Basics of Foraging
• Two components of foraging
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Basics of Foraging
• Two components of foraging
-- searching/finding = search time
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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
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Optimal Foraging Theory
• Test of OFT assumption:
-- calculated “optimal” diet of adult female
Columbian ground squirrels, based on plant
availability
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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
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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
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Optimal Foraging Theory
• Two decisions required of optimal foragers
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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)
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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
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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
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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
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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)?
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Diet Choice—the Man-Eaters of Tsavo
• In 1898, between 30-135 humans killed by lions in
southern Kenya while constructing Kenya-Uganda
railway.
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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
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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
