Community Ecology Concepts and Structures

Community Ecology Concepts

• Interactions among all species in a specific area at a specific time.
• Communities are dynamic and lack fixed boundaries.
• Species Interactions:
  • Negative-negative (e.g., competition)
  • Positive-negative (e.g., predation, parasitism)
  • Positive-positive (e.g., mutualism)

Ecotones and Abiotic Influences

• Ecotones: Transition zones between communities with higher species diversity.
• Examples include forest edges and soil transitions (e.g., serpentine soils).
• Environmental factors (e.g., temperature, resources) influence community structure.

Community Structures and Diversity

• Species Richness: Count of species within a community.
• Species Evenness: Distribution of individuals among species.
• Diversity: Combination of richness and evenness.

Why Communities Differ in Species Richness

• Resources: Intermediate productivity supports the highest species richness (hump-shaped curve).
• Habitat Diversity: More diverse habitats lead to greater richness.
• Disturbances: Frequency of disturbances can either stabilize or disrupt richness.
• Influential Species: Keystone or dominant species influence community dynamics.

Rank Abundance Curves

• Rank species by abundance to compare communities.
• Flatter curves indicate higher evenness.

Experimental Evidence

• Whittaker's study (Great Smoky Mountains): Gradual changes in species abundance with moisture levels suggest species independence.
• Experimental Communities:
  • Removing neighbors at low elevations improves fitness, suggesting independence.
  • Removal at high elevations reduces 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 favors dominant competitors, reducing diversity; intermediate productivity allows coexistence of specialists and generalists.

• Park Grass Experiment: Long-term fertilization reduces species richness, demonstrating one aspect of the hump-shaped curve.

• Light and Fertilizer Experiment: Adding light alongside nutrients restores species richness, indicating competition for light limits diversity.