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I.
Community Ecology
H.
Community Structure
1.
Species Diversity
•
a.
b.
Two components
Species richness
Relative abundance (evenness)
Fig. 54.10
I.
Community Ecology
H.
Community Structure
2.
Trophic Structure
•
•
Energy transferred between trophic levels
Simple model = food chain
Fig. 54.13
I.
Community Ecology
H.
Community Structure
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
Fig. 54.14
I.
Community Ecology
H.
Community Structure
3.
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 Structure
3.
Influential Species
a.
b.
c.
Dominant species
Keystone species
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 Structure
4.
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