Interference or Exploitation? A Second Look at Competition between Salamanders

Jaeger, Robert

Brief Description: Two closely related species of salamanders, Plethodon cinereus and P.nettingi shenandoah, were previously reported to compete for food through differentialexploitation. A more recent experiment, though, suggests that an interference component mayexist in competition for burrow position. Full Description: Interspecific competition is now thought by many ecologists to be a basic component instructuring communities. Yet, the mechanisms by which such competition operates are far fromclear in most cases. When competition is shown to occur, one often has difficulty indetermining even whether it is through interference or differential exploitation, let alone thespecific mechanism involved. Interference, as defined by Miller (1969), occurs when one speciesinhibits a competitor's access to a vital resource, by such mechanisms as interspecificterritoriality and aggression. Exploitation occurs when one species is merely more efficient inobtaining a share of a limited resource, even though individuals of both species have free accessto that resource. Jaeger (1970, 1971a,b, 1972) demonstrated that the terrestrial salamander Plethodon cinereus competitively excludes a sibling congener, P. nettingi shenandoah, from areas of deepsoil, forcing the latter into relict populations in suboptimal talus habitats. Data were presentedto support the conclusion that competition occurs for a limited food resource, and differentialexploitation was considered the mechanism involved (Jaeger, 1972), since no evidence could befound of aggressive interactions. While the exploitation hypothesis is still tenable, a subsequentexperiment indicates that interference may also occur, since at least one of these species iscapable of influencing the behavior of the other. Such behavioral interaction could provide amechanism for competitive interference.

Interference or Exploitation? A Second Look at Competition between Salamanders

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