Alpha Selection in Competing Salamanders: Experimental Verification of an a Priori Hypothesis

Abstract

Much ecological theory rests on the assumption that interspecific competition is exploitative, interference playing a small role. It is argued that interference mechanisms should evolve in many situations, and an example is described of an experimentally demonstrated result of the origin of interference competition. Large numbers of individuals of Plethodon Jordani from an area of intense competition with P. glutinosus were substituted for conspecifics in an area where competition was less severe. The population of P. glutinosus showed a statistically significant decrease relative to controls. Although the 2 spp. had been shown to compete with each other in the locality of this experiment, other experiments showed that they had virtually no effect on congeners in the area of intense competition. The combination of results demonstrates that .alpha.-selection (sensu Gill 1974) had taken place. Since .alpha.-selection certainly involves interference mechanisms, it is important to observe that a majority of the experimentally demonstrated examples of competition in the field have involved interference of some kind or other. The importance of these experimental outcomes for ecological theory is discussed.