28.7: Ecological Niches

All organisms have a position within an ecosystem. The complete set of living and nonliving factors—including food resources, climate, and terrain—that define the position of a given organism are collectively referred to as the organism’s ecological niche.

Multiple species cannot occupy the exact same niche within their habitat. If the niches of two or more species overlap to a large extent, the competitive exclusion principle dictates that one species will outcompete the other, forcing it to adapt or die out. However, flexibility in the resources an organism uses can allow similar species to coexist if they modify their realized niches to avoid competition.

Further, it appears that there is often a correlation between niche size and geographical range. Species with niches that are broader are generally found across a larger geographic area. Such larger distributions might give these species more flexibility in the realized niche, allowing them to adapt to environmental changes or the presence of competitors more easily than a species with a narrower niche and smaller geographic range.

Understanding how organisms function together in their ecosystem through their ecological niches can help guide conservation efforts for vulnerable areas and endangered species, as well as limiting the threat posed by invasive species.

An ecological niche describes the role of an organism within its environment. The niche includes the complete set of biotic, living, and abiotic, non-living, resources that the organism uses. For example, the niche of a hare includes abiotic factors, such as the climate in which it can survive, and the terrain that provides shelter and safety from predators.

Biotic factors might include the other hares it encounters, the plants that it consumes, and predators that feed upon it. A fundamental niche is the full set of resources that an organism could use in its environment, while a realized niche is the narrower set of resources that a species actually uses. Competition with other species is the major factor that limits the extent of the realized niche.

The species is typically more optimally adapted for these conditions, but it may use resources outside of the realized niche if its preferred resources are not readily available, or if competition from other species is removed. While there is often overlap in the resources used by similar species in a given area, multiple species cannot occupy the exact, same niche in an ecosystem, due to competition. One solution that arises over time is resource partitioning, a division of limited resources in an ecosystem that allows species to coexist rather than compete.

Ecologically similar species can either evolve to use different resources, or share the same resources, but use them at different times or places. A classic example of resource partitioning can be found in Robert MacArthur's work on warbler species in the woods of New England. MacArthur found that, although the warblers appear to use the same resources, inhabiting the same trees, and consuming the same insects, they actually occupy different areas of the trees. The spatial partitioning of resources was sufficient to allow five species of warblers to coexist within the same trees.