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BIO120.Lecture (3).docx

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Doug Thomson

BIO120: Physical Challenges of the Environment for Animals, Emphasis on Tradeoffs and Alternatives -concluding animal physiological ecology a) why can’t natural selection produce perfect adaptation? Tradeoff principle; weasel body shape b) brief comments on animal water balance; examples from kangaroo rat physiology & behavior c) alternatives: evading stressful times by dormancy, migration, storage -many believe that process of evolution by means of natural selection should produce perfection: we should not expect perfection -characteristic about weasel: long, thin, short-furred, extreme shape -slide 6: compares weasels to woodrats (more usually shaped, around same mass) -woodrat can roll into ball when it gets cold -weasel can only curl itself into a flat disk, cannot become more spherical, still has more surface area to volume than woodrat -therefore, weasels should live in warm climates; however, that species of weasel is a very northern species -something besides thermoregulation that is involved -what are advantages of being long and thin in cold climates? -shape associated with weasels role as predator: weasels are specialists on taking rodents that live underground, need to be able to fit into narrow burrow, gives them access to particular prey source they would otherwise not have access to -shape allows specialized role of underground predator -typical weasel prey: pocket gopher, seldom leaves underground burrows, is adapted for underground life, has small and poor eyes, large claws, small ears, fur- lined cheeks for harvesting food -by being long and thin, the weasel has access to this food supply, therefore, in winter the weasel is able to survive by eating more to keep up metabolism -being long and thin makes weasels subject to thermal stresses but allows them to be better predators -tradeoff: fitness gains of being a good hunter offset the fitness costs of an expensive metabolism -phenotypes of all organisms are riddled with compromises dictated by tradeoffs -natural selection cant maximize both proper shape and being able to burrow underground -tradeoff: being good at x may necessarily imply being bad at y -constraints: natural selection is decent with modification, most variations from parent species are subtle, selection builds on what is already there, especially existing developmental programs, selection is a tinkering process (small adjustments in phenotypes), will take a long time to develop an entirely new characteristic -all animals need water, some animals are dealing with this necessity in an environment where there is little water (kangaroo rat) -kangaroo rat: as long as they have an access to food supply, they don’t need free water in their diet  Anatomy: erect posture, bipedal (stand on two feet); less heat gain from ground  Physiology: super-efficient kidneys, metabolic water sufficient, good at eliminating waste from their body with minimal water, get water through breaking down fat molecules to produce water biochemically, they drink by eating “dry” food, as long as it has fat content in it  Behavior: nocturnal; spend hot days underground, cache seeds underground; recapture water vapour from exhalation, seeds are hydroscopic (a
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