DISPERSAL OF ANNUAL PLANTS IN HIERARCHICALLY STRUCTURED LANDSCAPES

The scale at which plants utilize spatially distributed resources may be determined by their ability to locate sites that can sustain popula tion growth. We developed a spatially-explicit model of the dispersal of annual plants in landscapes which were hierarchically structured, i .e., the spatial pattern of suitable sites was nested and scale-depend ent. Results show that colonizing ability and extinction probability a re most sensitive to the mean dispersal distance of the species. Dispe rsal out of the parental site, but within the immediate neighborhood, was the most efficient means for popolation expansion. When landscape patterns change with scale then dispersal distances determine the spat ial scales of habitat utilization. As a complicating factor, the type of statistical distribution of dispersal distances also influences the colonizing ability. However, the importance of dispersal distance mea n and distribution decreased as the number and connectance of suitable sites increased. The results suggest that landscape models which cons ider the interaction between scale dependent changes in landscape patt ern and species dispersal and establishment characteristics are releva nt to many issues in community ecology, invasion biology, and conserva tion biology.