Extinction and colonization dynamics in a Black Rail metapopulation: Roles of biogeographic versus habitat factors

The incorporation of habitat dynamics into metapopulation models has recently been an area of active theoretical development. Yet, the influence of habitat relative to classical biogeographic factors has rarely been investigated in real metapopulations, especially for vagile organisms. Here we report on the correlates of extinction and colonization in a metapopulation of Black Rails found in small (0.25-13 ha) wetlands in the foothills of the Sierras in central California. We conducted systematic presence-absence surveys using playbacks from 2002-2006 at 181 potential wetland sites on public and private lands. Using occupancy estimation models, the probability of detection (p) was estimated to be 0.863 per visit and differed little among years. Three survey visits are sufficient to generate a site-specific probability of detection (p*) > 99%. Rails were present on average in 56% of the sites surveyed. Turnover occurred frequently; the probability of local extinction (0.193) was slightly greater than colonization (0.163), with small differences among years. Biogeographic factors had a greater influence on the probability of extinction than characteristics of the matrix surrounding each patch, land use (grazing, ownership) and hydrology (water sources), using occupancy models and AIC approaches. Extinction rate was negatively related to patch perimeter, area, and fractal dimension as predicted from metapopulation theory. We present similar analyses for the correlates of colonization, and interpret these results in relation to regional land use change and development patterns.