Determinants of diversity in a naturally fragmented landscape: humid montane forest avifaunas of Mesoamerica

This forest type was originally widespread in the lowlands, and became restricted to mountains during Pleistocene climatic changes, such that the isthmuses of Tehuantepec and Panama acted as barriers to range expansion and peninsular effects catalyzed speciation, elevating numbers of endemic species.

Abstract

We used a published data set summarizing avifaunas of 31 montane patches of humid forest in Mesoamerica to analyze avian distributions with respect to site characteristics. This forest type was originally widespread in the lowlands, and became restricted to mountains during Pleistocene climatic changes. Hierarchical partitioning, a recently developed regression procedure, was used to examine independent factor effects. Total species richness, richness of Mesoamerican endemic species, richness of narrowly endemic species, and richness of habitat specialists were considered separately, each analyzed at three spatial scales. For total richness and Mesoamerican endemics, regional-level variables, notably latitude, were most influential. Narrow endemics exhibited more complex patterns, driven by foci both in western Mexico and in Costa Rica and western Panama. Historical factors are suggested to have contributed to this latitudinal pattern, such that the isthmuses of Tehuantepec and Panama acted as barriers to range expansion and peninsular effects catalyzed speciation, elevating numbers of endemic species. In contrast to many anthropogenic fragmentation studies, area and other local-scale patch attributes had little influence on avifaunas. This discrepancy may be related to fundamental differences in spatial and temporal scaling, with patterns uncovered herein more indicative of long-term community processes.