Effects of habitat loss, habitat configuration and matrix composition on declining wetland species

Worldwide declines in wetland birds and turtles are attributed to landscape-scale habitat loss, habitat fragmentation and anthropogenic land use. However, due to multi-collinearity, the relative importance of these factors is largely unknown. We evaluated the relative effects of wetland amount, wetland configuration (measured as the number of wetland patches), and matrix composition (measured as the amount of forest, cropland and road density) on the occurrence of eight declining wetland bird species and two threatened freshwater turtles across 66–70 landscapes. We selected landscapes to minimize correlations among the landscape-scale predictors and to represent the range of variation in each predictor available in the study region. For wetland birds, we found that the amount of wetland at a landscape-scale was more important than the other landscape variables, whereas surprisingly for turtles, the amount of forest in the surrounding landscape was more important than the other landscape variables. Wetland configuration independent of wetland amount was not an important predictor of any species. This is the first study to assess the relative, independent effects of the landscape-scale factors thought to contribute to wetland bird and turtle declines. Our results confirm that wetland loss is the primary landscape-scale factor of wetland bird declines, but suggest that forest loss may play a greater role in freshwater turtle declines than previously realized; minimizing forest loss will have the most positive outcome for freshwater turtle conservation. Therefore, effective conservation planning requires a multi-taxa approach to meet landscape-scale requirements of all declining wetland fauna.