Field Studies and a Simulation Model of Small Mammals Inhabiting a Patchy Environment

Current theories on the importance of dispersal and the results of field work conducted on small mammals inhabiting different habitat patches were used to construct a population dynamics simulation model. Reproduction and mortality were assumed to be time-dependent constants. Emigration rates were determined from the relative interspecific and intraspecific competition suffered by a given species at a given habitat and time. Immigration was assumed to be dependent on the size of the habitat, its distance from other habitat types, and habitat preference index. The model produced small mammal communities that exhibited similar trends in their compositions to those observed in the field study. Only in one treatment, the nitrogen + water treatment, did the model densities greatly differ from the observed densities. However the general trends of the population dynamics were similar. The model is not sensitive to small changes (±20%) in competition, mortality, and threshold density before emigration can occur. The model showed high sensitivity to small changes in the relation between competition and emigration and to small changes in the density of the species in the environment. Model experiments in which dispersal was prevented resulted in significant changes in the community compositions. When the habitat preference index of all species was set equal for all habitats, the differential habitat utilization exhibited by all species was partly removed because all species were found in all four habitats. The model results support the current theories on the importance of dispersal in determining species distribution and abundance.