BIO120 Lecture03

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Lecture 3: Physiological ecology of

animals: heat balance

1. Example of one environmental challenge tophysiology: Heat balance/thermal ecology ofanimals

a.

Modes of heat gain and loss; homeostasis

b.

Size, shape, insulation, evaporative cooling

c. Tradeoff principle and adaptive compromises(example of weasel body shape)

Copyright James D Thomson

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Radiationheat transfer by electromagneticradiation

Conductiondirect contact with substrate (e.g.,

feet lose heat to ground)

Convectionheat transfer mediated by movingfluid (usually air or water)

Evaporationefficient cooling from wet surfaces

Redistributioncirculatory system redistributesheat among body parts, esp. core toappendages

One selected limiting factor:

heat budgets


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Size matters to heat balance (and other

balances of gains and losses)

Homeostasis and surface area:volume ratio

Surface area determines equilibration rate

Volumeprovides the inertia

Radius: 1 2 3

SA/V: 3 1.5 1

Equilibrates most slowlyEquilibratesquickly


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Sizematters

Bergmanns rule: Homeotherms tend to

be larger at higher latitudes (colder)

Helarctos malayanus65 kg, short fur

Ursus americanus275 kg, medium fur

Ursus maritimus650 kg, long fur

All WikipediaCopyright James D Thomson

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Fossil record: horses shrank during two past

episodes of climate warming, grew during ice ages


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An exception to Bergmann

s Rule?

National Geographic


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Shapematters:

Allens rule: extremities reduced in cold

climates

Sphere has least SA:V, so why shouldnt

homeotherms be spheres in cold climates?

Sometimes SA is needed for function

Sometimes particular shapes are neededfor function

Tradeoffs and adaptive compromises


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Maximum SA:V ratio?

Chrysopelea gliding snake, Borneo;

restricted to warm tropics

National Geographic, Tim Laman


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Minimum SA:V ratio?

Pika, Ochotona princeps: alpine tundra rabbit;

restricted to cold habitats; note spherical shape,

reduced ears (for a rabbit)

National GeographicCopyright James D Thomson

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Variation in appendages: arctic and

desert hares

Lepus arcticus (Art Wolfe) Lepus californicus (www.pestproducts.com)


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What else matters? Insulation more

important than size/shape

www.dinosaur-museum.org

mercury.bio.uaf.edu


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Thick insulation: Half-sheared sheep

National GeographicCopyright James D Thomson

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What else matters? Shaving! Can aquatic

mammals use fur for insulation? Drag is a drag.

When shaving is not enough:Michael Phelps, 16 22 Olympic medals

HGH?

Anti-drag

suit


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Thick insulation: Cross-section of seal

Blubber

Guts

Musculature42%

58%of cross-sectional

area


f

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Hair and feathers provide

adjustableinsulation

Video clip, Clarks Nutcracker on a cold

morning in Colorado


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What else matters? Convective

cooling enhanced by vascularization

Lepus californicus(National Geographic) L. americanus (JDT)Copyright James D Thomson

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Another way to provide well-

vascularized surface area for cooling


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What else matters? Countercurrent

circulation to limbs conserves heat

Arteries and veins should be appressed in appendagesto conserve heat; separated in appendages designed to

shed heat (Compare Ricklefs Fig. 3.24)

Countercurrent flow maintains gradient, so heat isalways flowing from outgoing blood to incoming blood

Outside (0!"

Body (35!" 30 20

5 10

15

Body (35!"30 15

25 10

0

Vessels not appressed,returning blood is chilled Vessels appressed,returning blood is warmerCopyright James D Thomson

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What else matters?

Convection enhanced by evaporation

/www.bluegina.com


?

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What else matters?

Convection enhanced by evaporation

/www.bluegina.com


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Extra slide if time: Range dependence on other organisms:saguaro, gila woodpecker, cactus wren, elf owl

www.southwestbirders.comCopyright James D Thomson

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Reconciling an apparent paradox:

weasels are small predators, short-furred,very long and thin


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Weasel in winter = ermine: active all year;

camouflaged for snowy environment

23Copyright James D Thomson

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24Henry VIII: Low SA / V Mustela erminea: High SA / V

Holbein


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25Henry VIII: Better? Mustela erminea: Worse?Copyright James D Thomson

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Ecology53(5): 939-943 (1972)

Weasel WoodratWarm

((Cold))Curls into flat disk Curls into ball


So the weasel body plan is well suited

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So, the weasel body plan is well-suitedfor warm climates!

M.erminea

!making their actual distribution paradoxical!


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28Mustela frenataand Thomomys talpoides, Rocky Mountain Biological Lab, D. Inouye photosCopyright James D Thomson

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Typical weasel prey:

Pocket gopher,Thomomys talpoides

Seldom leaves

underground burrows;mostly eats roots, tubers

So, the paradoxinvolves

the requirements of theweasels predatory

lifestyle


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Example of a tradeoff:

Being long and thin makes weasels subject to

thermal stresses (costly)!

!but allows them to be better predators

(beneficial).

Because they are long and thin, we infer that the

fitness gainsof being a good hunter offset the

fitness costsof an expensive metabolism Phenotypes of all organisms are riddled with

compromises dictated by tradeoffs


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Two reasons why natural selection

produces deeply imperfect organisms

Tradeoffs

Being good atxmay necessarily imply being

bad at y

Constraints

Selection builds on what is already there,especially existing developmental programs

Tinkering, yes; fundamentally fresh redesign,

no

31Copyright James D Thomson

BIO120 Lecture03

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