Independent effects of habitat amount and fragmentation on songbirds in a forest mosaic

The degree to which spatial patterns of habitat influence the dynamics and distribution of populations is a central question in ecology. Habitat fragmentation may result in decreased patch colonization and increased rates of local extinction, both of which can result in population declines greater than expected from habitat loss alone.;Further, while landscape pattern is easily defined in island archepelagos or agricultural mosaics, identifying patterns in forested landscape is often subjective and rarely based on accurate estimates of what a species considers to be habitat.;In this dissertation I use a combination of research design and statistical methods to test for the independent effects of habitat loss and fragmentation on the occurrence of forest songbirds. I define landscape pattern using statistical distributional models that I developed for each species (i.e., an organism-based approach).;I found that the occurrence most species is influenced by characteristics at scales greater than the individual territory. Thus, habitat loss cannot be expected to result in a proportional decline in the number of animals living in a particular landscape.;Determining the relative importance of habitat loss versus fragmentation has been problematic. Because, in most circumstances, fragmentation occurs through a process of habitat loss, the effects of habitat amount and configuration are usually confounded. However, unless the influence of landscape pattern on populations is understood, conservation biologists will not know whether it is possible to design landscapes that mitigate the negative impacts of habitat loss.;The occurrence and reoccurrence of Seiurus aurocapilla depended on a landscape pattern variable---patch size---but only in cases when patches were isolated. These results support the hypothesis that landscape pattern is important only when the amount of suitable habitat is below a threshold.;However, the majority of variance in the occurrence of most species in this study was explained by either local scale, or landscape composition variables. Thus, the primary conservation focus should be on maintaining appropriate amounts of habitat.