Effects of Local and Landscape Processes on Animal Distribution and Abundance
Investigations of processes that drive animal distribution and abundance are often approached at one of two different scales and therefore focus on different processes. At local scales, animals are thought to select home ranges or territory patches in an ideal manner by occupying them in order of their fitness potential, but a variety of processes can decouple choices from their fitness consequences and create non-ideal patterns of distribution. At landscape scales, the spatial arrangement of habitat patches and their size and isolation are thought to influence distribution patterns because extinction probability declines with increasing patch area and colonization probability declines with increasing patch isolation. Although understanding the relative effects of local and landscape processes on distribution is essential for conservation, very few studies have explicitly considered the fitness potential or quality of habitat when doing so, especially at small scales relevant to the behavioral choices of individuals. I integrated behavioral and landscape approaches for understanding distribution by assessing the relative and combined effects of habitat quality at territory-specific scales and the effects of habitat amount, habitat configuration, and matrix structure at landscape scales on long-term occupancy dynamics of Ferruginous Pygmy-Owls over 12 years. To quantify habitat quality, I considered the estimated additive and interactive effects of habitat resources, stochastic factors (e.g., weather), and conspecific density on reproductive output based on extensive demographic monitoring over 10 years in the same territory patches.
Habitat resources explained a much greater proportion of variation in reproductive output than weather or conspecifics, but realized habitat quality was best described by the interactive effects of all these factors. High-quality habitats buffered the negative effects of conspecifics and amplified the benefits of favorable weather, but did not buffer the disadvantages of harsh weather. The positive, density-independent effects of favorable weather at low conspecific densities were offset by intraspecific competition at high densities. Habitat quality had greater effects than landscape processes on patch occupancy dynamics, and its effects were best described by interactions among habitat resources, weather, and conspecifics. Nonetheless landscape factors also had important effects: habitat amount had greater effects than habitat fragmentation or matrix structure, effects that were either positive or negative depending on local habitat quality. Although metapopulation theory is the dominant paradigm upon which many conservation strategies are based, improving local habitat quality may yield greater returns, especially when the surrounding landscape context is considered.