Lecture 15 Flashcards
how are ranges of tolerance related to homeostasis?
reactions occur (enzymes function) best at optimum temperature and osmotic conditions where fitness is maximised.
what does an animal’s physiology reflect?
the climate and other conditions to which the organism is adapted
compare the tolerance of temperate animals to tropical animals?
- temperate animals withstand colder temperatures than tropical animals
- temperate animals also tolerate a wider range of temperatures than tropical animals
trends in seasonal temperature variation
low near the equator and increases with latitude
heat balance in poikilotherms
most reptiles, amphibians, fish, invertebrates
- lack physiological means to deviate from environmental temperature (although they use behavioural means): their temperatures fluctuate
heat balance in homeotherms
must regulate heat balance to keep internal temperature within a narrow range: many traits contribute to this
why do poikilotherms have lower energy requirements than similarly sized homeotherms?
maintaining a constant internal temperature requires energy
list the 5 modes of heat gain or loss
radiation
conduction
convection
evaporation
redistribution
radiation
heat transfer by electromagnetic radiation
conduction
transfer by direct contact with substrate (eg feet lose heat to ground)
convection
heat transfer mediated by moving fluid (usually air or water)
evaporation
efficient cooling from wet surfaces
redistribution
circulatory system redistributes heat among body parts, esp. core to appendages
how does size matter to heat balance?
- surface area determines equilibration rate
- volume provides the inertia
draw a diagram for radius vs SA:V and equilibrium
Bergmann’s rule
homeotherms tend to be larger at higher latitudes (colder)
if a sphere has the smallest SA:V, why aren’t homethoerms always spheres in cold climates?
- sometimes SA is needed for function
- sometimes particular shapes are needed for function
- tradeoffs and adaptive compromises
who has the maximum SA:V ratio?
Chrysopelea gliding snake, Borneo; restricted to warm tropics
who has the minimum SA:V ratio?
American Pika, Ochotona princeps: alpine tundra rabbit; restricted to cold habitats; spherical shape, reduced ears for a rabbit
Allen’s rule
homeotherms tend to have smaller appendages at higher, colder latitudes
what other factors matter other than shape and size?
- insulation
- convective cooling enhanced by vascularisation
- evaporative cooling
- countercurrent circulation to limbs conserves heat
describe how countercurrent circulation to limbs conserves heat
- 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
draw a diagram for countercurrent circulation
how is the skinny weasel in cold climates an example of a trade-off?
- 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
two reasons why natural selection produces deeply imperfect organisms
- tradeoffs: being good at x may necessarily imply being bad at y
- constraints: selection builds on what is already there, especially existing developmental programs.
