Competition for resources is common in natural communities
How important is competition in natural communities? To answer this question, results from many field studies must be compiled and analyzed. The findings of three such analyses indicate that competition has important effects on many species.
For example, Schoener (1983) examined the results of 164 published studies on competition and found that of 390 species studied, 76% showed effects of competition under some circumstances, and 57% showed effects of competition under all circumstances tested. Connell (1983) examined the results of 72 studies and found that competition was important for 50% of the 215 species studied. Gurevitch et al. (1992) took a different approach: they did not report the percentage of species for which competition was important, but rather analyzed the magnitude of competitive effects found for 93 species in 46 studies published between 1980 and 1989. They showed that competition had significant (though variable) effects on a wide range of organisms.Surveys such as those by Schoener, Connell, and Gurevitch et al. face potential sources of bias, including investigators' failure to publish studies that show no significant effects and the tendency for investigators to study “interesting” species (i.e., those they suspect will show competition). Despite such potential sources of bias, the fact that hundreds of studies have documented effects of competition makes it clear that competition is common—though not ubiquitous —in nature. We explore the relative importance of competition to community structure in Chapter 19.