LANDSCAPE CONNECTIVITY AND POPULATION-DISTRIBUTIONS IN HETEROGENEOUS ENVIRONMENTS

Landscape connectivity refers to the functional relationship among hab itat patches, owing to the spatial contagion of habitat and the moveme nt responses of organisms to landscape structure. Heterogeneous landsc apes provide a particular challenge for modelling population-level res ponses to habitat fragmentation, because individuals may be utilizing multiple habitats to varying degrees across the landscape. We apply ne utral landscape models to understand how species' habitat affinities i nteracted with landscape structure (i.e., habitat abundance, distribut ion, and quality as measured by carrying capacity) to affect the redis tribution of individuals. Two types of neutral models are presented: r andom maps, in which the distribution of habitat is spatially independ ent and fractal maps, in which habitat exhibits an intermediate level of spatial dependence. The neutral landscapes comprised varying propor tions of three habitat types, for which species exhibited a preference gradient (high, medium, low). We performed a series of simulation exp eriments as a factorial design of parameter states to tease apart the underlying factors responsible for population distributional patterns (random vs clumped) in spatially complex mosaics. Landscape connectivi ty is a threshold phenomenon, in which even a minimal loss of habitat near the critical threshold (p(c)) is likely to disconnect the landsca pe, and which may have consequences for population distributions. The exact value of p(c) depends upon the spatial arrangement of habitat; f ractal landscapes exhibited connectivity across a greater range of hab itat abundance (p) than random maps (fractal p(c) = 0.29-0.50, random p(c) = 0.59). Although the spatial arrangement of habitat (random vs f ractal) was the most important determinant of population distributiona l patterns, different landscape factors were important in structuring populations in the two types of maps. The relative abundance of habita t had the greatest effect on populations in random landscapes, whereas scale-dependent patterns were evident in fractal landscapes. At fine scales, population dispersion was determined by habitat abundance in b oth random and fractal maps, although populations were more aggregated (as measured by Morisita's Index, I-m) at this scale in random landsc apes. But at coarse scales on fractal maps, population distribution wa s primarily influenced by species' habitat affinities. Assessment of t he independent effects of habitat affinity and habitat carrying capaci ty on population distributions revealed that the differential interact ion of species with landscape structure (i.e., different residence pro babilities in each habitat type) was the primary determinant of distri butional patterns. Neutral landscape models thus provide a useful tool for determining the relative importance of various components of land scape structure that affect population distributions.