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food webs.docx

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McMaster University
Kim Dej

November 8 , 2012 Biology 2F03: Fundamental and Applied Ecology Food Webs Food Webs - a food web is a summary of the feeding interactions in a community of species - a few keystone species may control the structure of a community - exotic predators may simplify the structure (and diversity) of food webs Feeding relations - to simplify description, graphic representations called food webs are used - example: a simple Antarctic food webs - major components: krill On the opposite pole - food web of Bear Island, Arctic - some differences include presence of land based predators - commonalities Question - are all the links all the same in the way they influence members of the community Tropical stream - Cano Volcan in Costa Rica and its food web - Weak links removed: food becomes simpler to analyze - 10 most common fish species and their food items: the web is very complex - strong interactions Question - what may influence food web properties in space and time Two food web comparison - subtropical vs. temperate - focus on different shapes and diversity - Robert Paine observed that a relatively simple temperate food web contained a relatively low proportion of predatory species - Temperate:  Only two predators; limited diversity  Top predator (pisaster)  Middle level predator (thois)  And 15 prey - tropical food web:  many more predators in the tropical food web; greater diversity  top predator  no. connection in need of testing  middle level predators (6)  prey (34 species)  does this prove that predation increases diversity? Keystone species experiement - starfish removal causes a diversity decline in two areas of the world - lesson: food webs are easy to disrupt; leads to loss of species Question - do top predato
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