Biology 3445F Lecture Notes - Lecture 16: Trophic Cascade, Herbivore, Keystone Species

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Trophic cascade manifestations (indirect effects) throughout a food web. Changes in the abundances of organisms at one trophic level can influence energy flow at multiple trophic levels. Top-down effects could be a director indirect effect of the predator on lower trophic levels. Bottom-up effects could be a direct or indirect effect of resource on higher trophic levels. Odd (cid:374)u(cid:373)(cid:271)er of trophi(cid:272) le(cid:448)els result i(cid:374) a (cid:858)gree(cid:374)(cid:859) (cid:449)orld. Even (cid:374)u(cid:373)(cid:271)er of trophi(cid:272) le(cid:448)els result i(cid:374) (cid:858)(cid:271)ro(cid:449)(cid:374)(cid:859) (cid:449)orld. Without predators at the top, competition will not regulate your population. Producers are driven to low levels without predators (brown because there are no plants) Diffs b/n the two maybe b/c freshwater ecosystems have 4 trophic levels. Producers grazing zooplankton planktivorous fish piscivores. Keystone species: proportionally greater impact on community structure than others (eg. greywolf in yellowstone national park) In real ecosystems, majority of species-interaction strengths are weak.

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