HOW ARE OAKS DISTRIBUTED IN THE NEOTROPICS? A PERSPECTIVE FROM SPECIES TURNOVER, AREAS OF ENDEMISM, AND CLIMATIC NICHES

Premise of research.The most important diversity hot spot of genus Quercus (Fagaceae) in America is situated in southern Mexico. From this area down to the Colombian Andes, oak species diversity decreases considerably, but the pattern of species distribution and turnover has not been analyzed. This study aimed at determining geographical patterns of species turnover, species distribution, and endemism for Neotropical Quercus species.Methodology.Occurrence records for 58 oak species belonging to the Quercus and Lobatae sections were obtained. Patterns of species turnover were determined by comparing species composition among latitudinal/longitudinal units. Areas of endemism were determined using weighted networks. The potential distribution of oak species was determined using ecological niche models. Finally, a principal component analysis was used to identify changes in the oak species' ecological niche across areas.Pivotal results.The species composition analysis indicated that the Tehuantepec Isthmus, the Nicaraguan Depression, and the Panamanian Isthmus represent species turnover points. Nine areas of endemism were recovered, distributed through mountainous ranges from Mexico to Costa Rica. Most of these areas were delimited by the species turnover points detected. Ecological niche modeling indicated that the turnover points represent areas with low climatic suitability for most oak species and represent discontinuities in the distribution of Quercus. Niche comparisons suggest niche differentiation among species distributed in different areas of endemism or on opposite sides of turnover points.Conclusions.The results indicate that the Tehuantepec Isthmus, the Nicaraguan Depression, and the Panamanian Isthmus have acted as important barriers to the dispersal of oak species, influencing species diversity, biogeographic patterns, and niche divergence.