Transcript Foraging
Key Points About Natural Selection 1) Natural selection operates within generations; evolution occurs between generations 2) Natural selection alters the properties of populations. 3) Natural selection is not forward thinking or directed in purpose. 3) Natural selection does not exist for the good of a species. Why Evolution by Natural Selection Works Individuals of populations exhibit genetically based variation in traits that affect survival and reproduction. NS and HIV Phenotypic Variation |-- Drought --| |-- Drought --| Hatchlings (1976) Hatchlings (1978) Evolution Occurs Between Generations Heritability of Beak Depth in Medium Ground Finches Adaptation ForagingCompetition Hypothesis Evolution is more than armchair science: hypotheses must be tested Prediction: If necks evolved for the purpose of foraging at the tops of trees, that’s where they should preferentially forage. Even during drought conditions Alternative Hypothesis: Necks are used as a weapon. Simmons and Scheepers 1996 Pratt and Anderson 1985 Things to keep in mind when studying adaptation • Differences among individuals are not always adaptive • Not every trait is an adaptation • Not every adaptation is perfect Tephritid flies: Do they mimic jumping spiders to escape predation? Phidippus Zonosemata Hypothesis 1: No mimicry Hypothesis 2: Mimicry deters other predators Hypothesis 3: Mimicry deters jumping spiders 20 spiders tested for each treatment Jumping spiders retreated Jumping spiders munched Adaptation: Observational studies of Thermoregulation in the Garter Snake Thermocouple/transmitter Options for Thermoregulation: Basking Cover Shade Rocks Moving up and down in burrows Prediction from observational data: Snakes should prefer medium sized rocks at night.