I. I.Community Ecology H. H.Community Structure 1. 1.Species Diversity Two components a. a.Species richness b. b.Relative abundance (evenness)

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I. I.Community Ecology H. H.Community Structure 2. 2.Trophic Structure Energy transferred between trophic levels Simple model = food chain

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I. I.Community Ecology H. H.Community Structure 2. 2.Trophic Structure Food chain concept often too simple Omnivory? Feeding by predator on multiple prey at different trophic levels Decomposers More realistic model = food web

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I. I.Community Ecology H. H.Community Structure 3. 3.Influential Species Some species have disproportionate impact on community a. a.Dominant species Highest abundance or biomass Usually superior at competition or avoiding predation b. b.Keystone species Occupy crucial ecological niches Removal can have profound effects on community structure

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I. I.Community Ecology H. H.Community Structure 3. 3.Influential Species a. a.Dominant species b. b.Keystone species c. c.Foundation species Engineers – Modify habitat through activity Ex: Beaver – Cuts down trees, builds dams Facilitators – Provide structure for habitat Ex: Black rush – Shades soil  reduced evaporation and salt buildup, oxygenates soil Fig. 54.9

I. I.Community Ecology H. H.Community Structure 4. 4.Control of Community Structure a. a.Bottom-up model Variation at lower trophic levels produces variation at higher trophic levels Ex: Fertilizing plants leads to increased biomass of large predators b. b.Top-down model Variation at higher trophic levels produces variation at lower trophic levels Ex: Removing top predators leads to increased biomass of primary producers