15.9–15.15: Species interactions influence the structure of communities.

The anemone (green) and the pink anemonefish live together. The anemone’s sting warns predators away, while the fish eats parasites and drives off fish that feed on anemones.

Within a society, most humans seem to find their niche. Each person plays a particular role, defined by the nature of his or her work, activities, and interactions with others. Other species do the same thing. Within their communities—geographic areas defined as loose assemblages of species, sometimes interdependent, with overlapping ranges—each species has its own niche.

We can think of an organism’s niche as its place in the community. More than just a place for living, however, a niche is a complete way of living. In other words, an organism’s niche encompasses (1) the space it requires, (2) the type and amount of food it consumes, (3) the organisms for which it is a food source, (4) its influence on competitors, (5) the timing of its reproduction (its life history), (6) its temperature and moisture requirements, and almost every other aspect that describes the way the organism uses its environment and influences the other organisms in that environment (FIGURE 15-20).

Figure 15.20: A way of living. “Niche” describes all of the ways in which an organism utilizes the resources of the environment.

Although a niche describes the role a species can play within a community, the species doesn’t always get to have that exact role. It is common for species to find themselves competing with other species for parts of a niche, and for one of the species to be restricted from its full niche (see Figure 15-20). Consider the rats of Boston. Until the 1990s, they lived in relative peace in the sewers beneath the city’s streets. But when the city embarked on the largest underground highway construction project in U.S. history, engineers displaced and forcibly drove out thousands of rats from much of their habitat. In essence, there was suddenly an overlap between the rat niche and the human niche, and the rats were now restricted to just some portions of the sewers. As a result, the rats’ realized niche, the narrower role that they may occupy in a community, is now just a subset of their fundamental niche, the full range of environmental conditions under which they can live.