Topic+15.+Food+webs

Topic+15.+Food+webs - Topic 15 Food Webs I Trophic levels...

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Topic 15. Food Webs I. Trophic levels of the food web ( Def. of food web : a representation of who eats whom) Example: grassland of NA slide A. Producers : Green plants that photosynthesize and drive the food web by capturing energy from sun and making food for the rest (directly or indirectly). B. Herbivores : They eat the producers. Most common type insects, but also mammals. C. Carnivores (= predators proper): Shown as intermediate here, eat animals (herbivores or other carnivores). Top carnivores (= top predators) have no predators on themselves. D. Decomposers : consume dead organisms; decomposers are mostly bacteria and fungi. II. Species can also interact without eating one another A. Examples are interference competition and mutualism. B. Sometimes these are included and then get “interaction web.” III. Competition for food (exploitative) occurs when two species eat the same lower-level food species e.g. coyote and owl both eat vole in grassland food-web.
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IV. What is dominant interaction (of competition and predation) at different trophic levels? Propositions: A. If there is no predation on a group of species, competition will dominate. True for top predators. B. If there is strong predation on a group of species, prey species will not be abundant enough to compete, and predation, not competition, controls them. C. If there are strong physical factors (storms, waves), these can affect A & B as follows: 1. If physical factor lowers the competing species’ abundances a lot, competition is reduced.
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