community ecology Ecological niches

An ecological niche encompasses the habits of a species. Essentially it refers to the way a species relates to, or fits in with, its environment. As a species adapts to the physical parameters and biota within the community, natural selection favours the development of specialized features that allow the species to uniquely exploit the surrounding resources. Physical conditions of the region—such as temperature, terrain, or nutrient availability—help to mold the niche, and biological constraints such as predation, competition, or lack of resources limit the ways in which a species exploits its environment. For example, plant species differ in their requirements for light, nutrients, and microorganisms, as well as in their ability to fend off competitors and herbivores. Herbivore species can eat only a subset of the plants available within a community, and predators can capture only some of the many potential prey species. Thus the species “carves out” a niche for itself in the community (see below Interspecific interactions and the organization of communities: Competition: The effects of competition).

An example of one such niche is that of the endangered Kirtland’s warbler (Dendroica kirtlandii) found in North America. It nests only among young jack pines (Pinus banksiana) that are 2 to 4 metres (6.5 to 13 feet) tall and grow in homogenous stands. These trees are exposed to periodic fires, necessary for germination of the jack pine seeds. These fires also continuously provide extensive new regions of young trees, allowing the warblers to shift their nesting sites over the years to remain within stands of jack pine that are of the preferred height.

The niche of a species evolves as physical and biological factors in the community change—provided that such changes are slow enough to allow species to adapt to them. The main constraint on this evolution is that no two species in a community can have the same niche. Specialized modes of existence thus provide a selective advantage to coexistent species, offsetting direct competition for available resources.