ECOL 182R 1st Edition Lecture 22 Outline of Last Lecture I Coexistence II Predator prey dynamics A Limit population sizes B Competing prey coexist Outline of Current Lecture I Predator adaptations A Generalized specialized B Choosing prey II Prey adaptations A Life Dinner Principle III Coevolution IV Community A Food webs Current Lecture Do prey predator really drive each other s cycles Gause tested this hypothesis in the lab with Didinium predator and Paramecium prey When put together in a flask with food provided for prey Both of them went extinct Why Predators ate all prey then they starve to death Nobody in the flask in a very short time Put in flask with a place for the prey to hide Predator only crashed not prey Why They predators ate what they could find then starve to death And the hiding prey survive Put in flask with periodic addition of more prey The cycles were observed But didn t last that long Eventually both died out The more complex he made it the more cycles he could get Predator adaptations Predator diets may be generalized most large vertebrates or specialized most small herbivores Or other weird cases like anteaters who are large vertebrates who aren t generalists but specialize in ants Why be a specialist More efficient Why be a generalist It s less risky less likely to run out of food So it s a trade off efficiency risk Both strategies work How should generalists choose prey Most common most nutritious least dangerous easiest to catch Most aren t conscious They try to maximize energy meal minimize time spent getting it Which explains why commin low quality prey are ignored And why rare high quality prey are ignored And why young sick and elderly are preferred Prey adaptations Life dinner principle natural selection is stronger on prey than predators Failure results in loss of dinner for predators but loss of life for prey Ways to avoid predators Be faster be cryptic hide in a herd Defenses if caught Ex toxic plant compounds that poison herbivores Caffeine inhibits herbivore DNA synthesis Coevolution simultaneous evolution of interacting species Like an escalating arms race Ex Faster linx faster hares Plants with more poison insects better able to detoxify them Character displacement like the different beaks on different islands involved coevolution of competitors Coevolution of mutualists match between species gets better better Community Ecology Community all species living in the same place at the same time They include lots of populations What properties characterize communities Trophic who eats who Fundamental law of ecology the maximum number of individuals in any community is limited by flows of food energy Trophic levels Producers plants get energy from the sun Detritivores decomposers eat detritus Dead stuff Primary consumers herbivores eat plants Secondary consumers eat primary consumers Tertiary consumers eat secondary consumers Doesn t usually get higher than this Omnivores feed at 1 trophic level Food chain links trophic levels to show who eats who Food web network of food chains more realistic
View Full Document
Unlocking...