Extinction and Spatial Structure in Simulation Models

Aspects of within-population spatial structure are often neglected in the modeling of population viability. To analyze the relevance of the spatial structure of single populations to population persistence, we compared the results of three models developed for the territorial, arboreal gecko Oedura reticulata: (1) a spatially structured model in which both low and high densities incur mortality costs due to increased movement, (2) a spatially structured model in which the Allee effect is removed, and (3) a spatially unstructured model in which there are no effects of density on mortality. Compared with nonspatial model populations, spatially structured populations exhibited reduced persistence. The Allee effect contributed only a small amount to the reduction in persistence. Increased mortality at high densities caused by difficulties in finding territories markedly reduced persistence in the spatially structured models compared with the density-independent nonspatial model. We argue that the inclusion of elements of spatial structure may considerably influence the estimation of extinction risk in population viability analyses.