Patch size matters for amphibians in tropical fragmented landscapes

Abstract

Several factors may affect the persistence of amphibian species in tropical fragmented landscapes, including the size of remaining patches. While fragment size is considered the main factor acting on species diversity for most taxa, it is less clear how it affects amphibian diversity. A possible reason is that the scale at which previous studies were conducted was too small (only few forest fragments and/or a small range of fragment sizes considered) and/or the sampling method was not the most optimal one. We investigate whether amphibian diversity is affected by patch size in the largest study (in terms of number of fragments and range of fragment sizes) ever conducted in tropical forests. We predicted that larger forest remnants hold higher amphibian diversity compared to smaller patches, and that continuously forest sites were more diverse than forest fragments. We used the visual encounter survey method to collect data from 24 sites (21 forest fragments between 1.9 and 619ha and three sites within a large continuous forest remnant) located in the Brazilian Atlantic Forest, a highly threatened biodiversity hotspot. We recorded a total of 2839 individuals from 50 species. In line with our predictions, larger fragments had more species, more integer communities and a larger diversity of reproductive modes than smaller ones. In addition, we found higher values for all diversity measures in continuous forest sites compared to fragments. These results indicate that continuous forests are irreplaceable for amphibian conservation, but also show that large forest fragments outside these areas are important for sustaining amphibian diversity. Our study provides robust empirical evidence for the importance of fragment size for amphibian persistence in tropical fragmented landscapes and highlights the need for an adequate sampling design and method that enable the detection of a higher number of species.