Nonlethal Injury to Organisms as a Mechanism of Population Regulation

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Abstract
Nonlethal injury and the loss of body parts, including autotomy, that are caused by intraspecific and interspecific contact are common features of many organisms. Such loss can adversely affect survival and reproduction of both males and females until regeneration occurs. The rate of injury is likely to be positively related to prey density. Two models that capture these features are presented. They predict that the susceptible population comes to a stable equilibrium if nonlethal injury reduces survival or reproduction or both. If injury is caused by another species, then the growth rate of the predator population must be coupled to prey density - and, hence, to the amount of injury - for stability to occur. In some salamanders, tail loss prevents reproduction (Maiorana 1977) and may explain observed population-size stability and the occurrence of reproductive and nonreproductive components in the population. In general, the injury models predict stable population dynamics, whereas the dynamically similar Lotka-Volterra predation model is less stable. I suggest that nonlethal injury may play an important role in the regulatory biology of population size in many species.