I. Community Ecology

H. Community Structure1. Species Diversity

• Two components

a. Species richness

b. Relative abundance (evenness)

Fig. 54.10

I. Community Ecology

H. Community Structure2. Trophic Structure

• Energy transferred between trophic levels• Simple model = food chain

Fig. 54.13

I. Community Ecology

H. Community Structure2. 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

Fig. 54.14

I. Community Ecology

H. Community Structure3. Influential Species

• Some species have disproportionate impact on community

a. Dominant species• Highest abundance or biomass• Usually superior at competition or avoiding

predation

b. Keystone species• Occupy crucial ecological niches• Removal can have profound effects on

community structure

Fig. 54.17

Fig. 54.18

I. Community Ecology

H. Community Structure3. Influential Species

a. Dominant species

b. Keystone species

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. Community Ecology

H. Community Structure4. Control of Community Structure

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. 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