Community Ecology
Community ecology is the interactions between and among populations of species over time and space within a specified area. Species interactions underlie ecosystem functions such as nutrient cycling and influence ecosystem structure. Understanding the community ecology of an area can guide management of species as well as land management of a given area.
Recall the diagram (figure 4.1) from the previous chapter on “systems”? An ecological community is generally defined as interacting populations of species. Although this text won’t dive into the nuances of delineating an ecological community, it may be helpful to quickly list the key delineating approaches:
- Physical boundaries, based on ecological site(s), differences of land uses (e.g., natural forest vs. cropland), physical land features (e.g., valley bounded by mountain range), ecotones (e.g., woodland to grassland), management units (e.g., ranch), or geopolitical area (e.g., Bureau of Land Management [BLM] land).
- Habitat boundaries, based on habitat characteristics of one or more key species (e.g., habitat of elk—mountains and valley)
- Interaction boundaries, based on areas of interaction between key species (e.g., eagle and small mammal—forest edge and valley)
- Ecosystem-type boundaries, based on ecosystem (e.g., forest or wetland).
Section 1: Properties of Ecological Communities
Ecological communities have three key properties: richness, diversity, and community structure.
Community Richness
Species richness is the count of species in a given area. It is a simple indicator of biodiversity. Its application is limited in that it is simply a count with no weight given to any specific type or class of species, such as endemic, or functional groups (e.g., nitrogen fixers or mesopredators). A community may have a high count of small mammal species, but what does that mean for the structure and function of that community and ecosystem?
Community Diversity
Species diversity is the count of different species (richness) and the relative abundance of those species (evenness). In figure 5.2 the communities have the same number of species (five), but Community A is essentially a monoculture of cheatgrass (Bromus tectorum), while community B presents a more even balance and distribution among species.
Community Structure
Community structure is species richness and diversity as well as the spatial and temporal distribution of species in the community. Community structure is determined by climate, geography, disturbances, and the interactions in section 2 and their influences covered in sections 3 and 4 below.
Section 2: Species Interactions
The study of community ecology focuses on interspecific interactions: competition, predation, and symbiosis.
Competition Interactions
Competition occurs between individuals of two (or more) species or populations of species utilizing the same resource in a given area. For example, elk (Cervus canadensis) and black-tail deer (Odocoileus hemionus)