The study of species diversity patterns and their causes remains a central theme of ecology. Work conducted over the last few decades has shown that both historical and ecological factors are important in determining species diversity patterns. Additionally, different causal mechanisms are important at different spatial and temporal scales. At the regional scale, species diversity patterns can best be studied in terms of three diversity components (alpha, beta and gamma). This study used the amphibians and reptiles of Costa Rica to examine these species diversity components at the regional scale. To accomplish this, existing species lists were compiled from the literature. Additionally, three herpetofaunal surveys were conducted at under surveyed sites to fill knowledge gaps. A survey of Parque Nacional Carara, a transitional zone site on Costa Rica's central Pacific coast, gave evidence of a rich herpetofauna, containing species from both the dry tropical forest to the north and the wet lowland forest to the south. Survey results show that Carara's herpetofaunal assemblage is more similar to that of the wet forest than the dry forest, and suggest many species from both assemblages reach their range limit at or near the park. Surveys of four sites in the eastern Area de Conservacion Guanacaste showed rich herpetofaunal diversity and validated the newly purchased Rincon Rainforest as an important conservation area. A survey of Reserva Natural Absoluta Cabo Blanco provided a preliminary list of amphibian and reptile species of the lower Nicoya Peninsula and highlighted the importance of Laguna Balsitas to the local amphibian fauna. A comparison of amphibian and reptile alpha diversity among 17 sites throughout Costa Rica showed highest alpha amphibian diversity in the lowland rainforests of the Pacific versant and highest reptile alpha diversity in lowland rainforests of the Atlantic versant. An analysis of beta diversity produced dendrograms showing sites within lowland ecoregions being most similar. A Canonical Correspondence Analysis (CCA) of environmental variables showed two climate gradients, an elevation/temperature gradient and a sun/rain gradient, to be important in determining species diversity patterns for both amphibians and reptiles in Costa Rica.
