Biology 250 Predation/Herbivory 3/2/2010 Predators and herbivores can act as agents of selection Predation-Herbivory Everything has to eat so there?s a constant pressure to survive and reproduce Positive/negative interaction Shark slide Tiger shark numbers went down, therefore the skate population went up The bay scallop population went up when the Tiger shark population went down but went down when the skate population went up Red Queen hypothesis Reed warbler slide Cuckoo?s lay their eggs in a warbler nest Cuckoo eggs look similar to the warbler egg, so the warbler doesn?t throw it out Parasitism led to a reduction in the difference in how the warbler eggs look Wasp slide B and C look like wasps but aren?t B is a Mantid C is a moth Snake slide Looks like a snake but is a moth caterpillar Frogs slide Advertising by colors that your poisonous Aposematism ? organisms with deadly or noxious defenses possess conspicuous warning signals These are not always honest Monarch butterflies Tastes really bad to predators Batesian mimicry ? resemblance of an edible to an unpalatable Viceroy mimic the monarch butterfly but viceroy is not toxic King snake mimics the coral (poisonous) Coral snake graph slide Data indicates that mimics are avoided in areas where coral snakes are present Predators avoid look alikes when the real thing is around Why does the yellow-eyed ensatina have yellow eyes? Genetics Avoid predation The mimic has yellow eyelids instead of yellow eyes Researchers caught wild jays and euthanized the salamanders and observed how long it took the jays to attack each species The jays weren?t interested in the poisonous ones but went right after the control Some jays avoided the mimic but others didn?t Showed that mimics survived longer than the control Write a paragraph press release for Thursday Mullerian mimicry ? mutual resemblance of two or more species to reinforce avoidance by predators Reduces predation in all species involved Both species are mildly toxic Herbivory Most terrestrial ecosystems lose 15-20% of biomass each year to predation Why is the world green? Herbivores are limited by predation Plants have traits to limit herbivory (the world is prickly and tastes bad) Chemical defenses Associational defense Plant species growing together reduces leaf damage of the plant species Masting Reproductive strategy where all reproductive effort comes in one shot Ex. oaks making lots of seeds in a masting year Induced defenses Shared signals Communication between plants using chemical emissions What do herbivores do about these defenses? Co evolutionary arms race Milkweed slide Caterpillars bite the plant and lets the latex bleed out so it doesn?t affect them How do you measure herbivory? Set up fences in GSMNP and measured the effect that deer had on plants Much thicker vegetation inside the fence (no deer) Deer have a big impact on plant populations Woody species are able to dominate outside the fence
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