Dispersal in White-Crowned Sparrows: A Computer Simulation of the Effect of Study-Area Size on Estimates of Local Recruitment

Abstract

Abstract Consideration of the problem of sampling a population within a finite study area suggested that recruitment results might be related to the size of the study area. Specifically, the proportion of recruits observed within a defined study area that originate in that area (local recruits) should be a function of the proportion of the population that the study area represents. Computer simulations of dispersal, using Nuttall's White-crowned Sparrow (Zonotrichia leucophrys nuttalli) as a model, were designed to test this hypothesis, and the effect of territory size and population size on this relationship. The simulations confirmed that local recruitment is a function of the proportion of the population sampled in the study area. Additionally, these simulations demonstrated that by holding the distribution of dispersal distances constant, local recruitment for a given proportion of the population sampled increased with territory size and population size. These latter results, however, are artifacts of the simulations and have no biological significance. Finally, the proportion of local recruits predicted for a natural population was remarkably close to that obtained from fieldwork. I suggest that conclusions about dispersal and population structure should not be drawn from proportions of local recruitment within finite study areas, and require more detailed analysis of dispersal.