Revirets lönsamhet och populationens stabilitet – kan populationer regleras socialt?

Abstract

Although Wynne-Edwards' group selectionist theory of population regulation was soon rejected, the concept of social regulation still remains in the literature. Here I examine the importance of social behaviour (e.g. territoriality) in population regulation from an individual selectionist point of view. One of Watson and Moss' criteria for population regulation through social behaviour is that the individuals should defend resources that exceed their need for survival and reproduction. This is an analogy to Verner's super territory model which is not compatible with optimality theory. Moreover, the observations that per capita reproductive rate decreases with increased group size has often been taken as a sign of social regulation at the group level. However, it can be demonstrated, both theoretically and empirically, that population rate of increase as well as the population's efficiency of converting resources into reproduction can increase with increased population density in spite of a decrease in per capita reproductive rate. These correlations reduce population stability in variable environments. To be effectively regulative social behaviour must induce a negative correlation between efficiency of converting resources into reproduction and population density. With this background I conclude that the importance of social regulation is highly exaggerated. It is only in a special case that social behaviour can induce population stability in variable environments, viz. in permanently territorial species whose life expectancy exceeds the average time period of the environmental fluctuations.