What is the importance of local and landscape environmental factors to the abundance and distributions of species in fragments of habitat? This issue has been extensively studied in recent decades, but often focusing on the primacy of one scale over the other. Here we advocate the alternative view of an interplay between processes at the local and landscape scales. We investigated the role of local and landscape environmental factors on the density of habitat specialists and generalists anurans in grassland landscapes of southern Brazil, known as Brazilian Southern Grasslands (BSG). Because anurans are dependent on waterbodies for reproduction and the original habitat matrix contrasts with current human-altered matrix, we hypothesize that anurans will be influenced both by local (waterbodies microhabitat) and landscape environmental factors. We also hypothetized that these effects are more important for species whose range is restricted to the BSG Ecoregion (specialists). We surveyed 187 waterbodies distributed over 40 landscape sample units (LSU, 2 x 2 km) during the spring of 2011-2014, through the 'active search in breeding sites' method. For each waterbody, 35 local environmental factors (structural heterogeneity) were measured. Each LSU was embedded in a larger habitat unit, called regional sampling unit (RSU, 8 x 8 km). For each LSU and RSU 16 landscape metrics were taken from a land use and land cover map. To assess the importance of local and landscape factors we used Generalized Linear Mixed Model following a protocol with five steps of selection of relevant predictor variables. With the final model we could predict the density of specialist on optimal local conditions. The difference of the predicted and observed values provided a quality index of each waterbody.
Results/Conclusions
We recorded 34 species, nine of which are specialists of the BSG. The specialists was affected by 12 local and 2 landscape environmental factors, while generalists by 14 local environmental factors. Thus, specialist and generalist presented different relationships with local and landscape factors. The model selection approach suggested that local factors have a major influence on the density of anurans than the landscape factors. However, the landscape has an indirect influence on local factors because higher quality waterbodies are located in landscapes with higher percentage of natural habitat. Generalist were affected by local factors of waterbodies. In conclusion, reproductive sites with higher local quality and within landscapes with larger percentage of natural grasslands are essential for the conservation of these anuran in the BGS.