Lecture 15

Question 1

how are ranges of tolerance related to homeostasis?

Answer 1

reactions occur (enzymes function) best at optimum temperature and osmotic conditions where fitness is maximised.

Question 2

what does an animal’s physiology reflect?

Answer 2

the climate and other conditions to which the organism is adapted

Question 3

compare the tolerance of temperate animals to tropical animals?

Answer 3

• temperate animals withstand colder temperatures than tropical animals
• temperate animals also tolerate a wider range of temperatures than tropical animals

Question 4

trends in seasonal temperature variation

Answer 4

low near the equator and increases with latitude

Question 5

heat balance in poikilotherms

Answer 5

most reptiles, amphibians, fish, invertebrates
- lack physiological means to deviate from environmental temperature (although they use behavioural means): their temperatures fluctuate

Question 6

heat balance in homeotherms

Answer 6

must regulate heat balance to keep internal temperature within a narrow range: many traits contribute to this

Question 7

why do poikilotherms have lower energy requirements than similarly sized homeotherms?

Answer 7

maintaining a constant internal temperature requires energy

Question 8

list the 5 modes of heat gain or loss

Answer 8

radiation
conduction
convection
evaporation
redistribution

Question 9

radiation

Answer 9

heat transfer by electromagnetic radiation

Question 10

conduction

Answer 10

transfer by direct contact with substrate (eg feet lose heat to ground)

Question 11

convection

Answer 11

heat transfer mediated by moving fluid (usually air or water)

Question 12

evaporation

Answer 12

efficient cooling from wet surfaces

Question 13

redistribution

Answer 13

circulatory system redistributes heat among body parts, esp. core to appendages

Question 14

how does size matter to heat balance?

Answer 14

• surface area determines equilibration rate
• volume provides the inertia

Question 15

draw a diagram for radius vs SA:V and equilibrium

Question 16

Bergmann’s rule

Answer 16

homeotherms tend to be larger at higher latitudes (colder)

Question 17

if a sphere has the smallest SA:V, why aren’t homethoerms always spheres in cold climates?

Answer 17

• sometimes SA is needed for function
• sometimes particular shapes are needed for function
• tradeoffs and adaptive compromises

Question 18

who has the maximum SA:V ratio?

Answer 18

Chrysopelea gliding snake, Borneo; restricted to warm tropics

Question 19

who has the minimum SA:V ratio?

Answer 19

American Pika, Ochotona princeps: alpine tundra rabbit; restricted to cold habitats; spherical shape, reduced ears for a rabbit

Question 20

Allen’s rule

Answer 20

homeotherms tend to have smaller appendages at higher, colder latitudes

Question 21

what other factors matter other than shape and size?

Answer 21

• insulation
• convective cooling enhanced by vascularisation
• evaporative cooling
• countercurrent circulation to limbs conserves heat

Question 22

describe how countercurrent circulation to limbs conserves heat

Answer 22

• arteries and veins should be appressed in appendages to conserve heat; separated in appendages designed to shed heat
• countercurrent flow maintains gradient, so heat is always flowing from outgoing blood to incoming blood

Question 23

draw a diagram for countercurrent circulation

Question 24

how is the skinny weasel in cold climates an example of a trade-off?

Answer 24

• being long and thin makes weasels subjects to thermal stresses (costly) but allows them to be better predators (beneficial)
• because they are long and thin, we infer that the fitness gains of being a good hunter offset the fitness costs of an expensive metabolism
• if they can get enough prey they can stay warm despite their heat-wasting shape

Question 25

two reasons why natural selection produces deeply imperfect organisms

Answer 25

• tradeoffs: being good at x may necessarily imply being bad at y
• constraints: selection builds on what is already there, especially existing developmental programs.