8.5 Community Ecology

Describe the structure of a community according to its species composition and diversity.

• The structure of a community is measured and described in terms of species composition and species diversity. Relevant equation: Simpson’s Diversity Index— Diversity Index = −∑ n N1 2 where n = total number of organisms of a particular species N = total number of organisms of all species

Explain how interactions within and among populations influence community structure.

• Communities are groups of interacting populations of different species that change over time based on the interactions between those populations.
• Interactions among populations determine how they access energy and matter within a community.
• Relationships among interacting populations can be characterized by positive and negative effects and can be modeled. Examples include predator/prey interactions, cooperation, trophic cascades, and niche partitioning.
• Competition, predation, and symbioses, including parasitism, mutualism, and commensalism, can drive population dynamics.