Community Ecology Concepts PDF

Structure Community Ecology: Concepts Definition: Interactions among all species in a specific area at a specific time. Communities are dynamic with no set boundaries. Species Interactions: ○ Negative-negative (e.g., competition). ○ Positive-negative (e.g., pred...

Structure Community Ecology: Concepts Definition: Interactions among all species in a specific area at a specific time. Communities are dynamic with no set boundaries. Species Interactions: ○ Negative-negative (e.g., competition). ○ Positive-negative (e.g., predation, parasitism). ○ Positive-positive (e.g., mutualism, though not covered here). Ecotones and Abiotic Influences Ecotones: Transition zones between communities with higher species diversity. Examples: Forest edges, soil transitions (e.g., serpentine soils). Environmental conditions influence community structure (e.g., temperature, resources). Community Structures and Diversity Species Richness: Count of species in a community. Species Evenness: Distribution of individuals among species. Diversity: Combination of richness and evenness.  Rank Abundance Curves: ○ Rank species by abundance to compare communities. ○ Flatter curves = higher evenness. Why Communities Differ in Species Richness Influences: ○ Resources: Intermediate productivity promotes the highest species richness (hump-shaped curve). ○ Habitat Diversity: More niches lead to greater richness. ○ Disturbances: Frequency can stabilize or disrupt richness. ○ Influential Species: Keystone or dominant species affect community dynamics. Experimental Evidence: Whittaker's Study (Great Smoky Mountains): ○ Gradual rise and fall of species abundance with moisture levels suggests species independence. Experimental Communities: ○ Removing neighbors at low elevation improves fitness, suggesting independence. ○ At high elevation, removal decreases fitness due to harsh conditions, suggesting interdependence. Competition and Resource Availability CSR Triangle: ○ C: Competitive ability. ○ S: Stress tolerance. ○ R: Ruderal (weedy traits for colonization). ○ Species allocate energy based on survival strategy. Resource Availability and Competition: ○ High productivity = dominance by strong competitors, reducing diversity. ○ Intermediate productivity supports co-existence of specialists and generalists. Case Studies: Park Grass Experiment: ○ Long-term fertilization reduces species richness, showing one side of the hump-shaped curve. Light and Fertilizer Experiment: ○ Adding light alongside nutrients restores species richness, indicating competition for light limits diversity.