Spatio-temporal variation in edge effects on the herpetofauna of a Mexican tropical rain forest

Edge effects associated to habitat fragmentation can vary depending on time and spatial details. Such aspects of edge effect on tropical herpetofaunas have not been assessed by considering simultaneously different seasons and edge orientations. We evaluated climatic seasonality and north-south effects on amphibian and reptile species abundance and composition across a pasture-edge-interior ecotone in a highly fragmented tropical rainforest at Los Tuxtlas, Mexico. We sampled six forest remnants and the surrounding anthropogenic matrix along transects comprising pasture, forest edge and forest interior (hereafter edge habitats). Three permanent transects per habitat were sampled six times between June 2003 and April 2005, recording all visual encounters of amphibians and reptiles with standardized diurnal and nocturnal sampling efforts. Overall, we registered 1111 individuals of 41 reptile species and 2265 individuals of 23 amphibian species. Reptile abundance and composition showed a strong edge habitat effect, and this effect changed with seasons. We did not detect a direct and strong edge habitat effect on amphibians' abundance and composition, while seasonality and orientation effects were crucial in defining edge and interior habitat patterns, with almost twice the number of individuals and species in north-faced than in south-faced ecotones. In a broader context, edge effect on amphibians and reptiles at Los Tuxtlas differs from edge effects in high elevation and more equatorial sites in that a high number of species were found inhabiting and using the surrounding matrix habitat, and exhibiting a strong effect of seasonality and orientation. Our results lead to recommend maintaining connectivity corridors and herps friendly productive systems to facilitate matrix- and edge-tolerant species dispersal among fragments, and to protect large fragments that provide high quality habitat for forest interior species.