Environmental correlates of leguminosae species richness in Mexico: Quantifying the contributions of energy and environmental seasonality

Explaining species richness patterns is a central issue in ecology, but a general explanation remains elusive. Environmental conditions have been proposed to be important drivers of these patterns, but we still need to better understand the relative contribution of environmental factors. Here, we aim at testing two environmental hypotheses for richness gradients: energy availability and environmental seasonality using diversity patterns of the family Leguminosae across Mexico. We compiled a data base of 502 species and 32,962 records. After dividing Mexico into 100 × 100 km grid cells, we constructed a map of variation in species richness that accounts for heterogeneity in sampling effort. We found the cells with the highest species richness of legumes are in the Neotropical region of Pacific coastal and southern Mexico, where the legume family dominates the tropical rain forests and seasonally dry tropical forests. Regression models show that energy and seasonality predictors can explain 25% and 49% of the variation in richness, respectively. Spatial autocorrelation analysis showed that richness has a strong spatial structure, but that most of this structure disappears when both energy and seasonality are used to account for richness gradient. Our study demonstrates multiple environmental conditions contribute complementarily to explain diversity gradients. Moreover, it shows that in some regions, environmental seasonality can be more important than energy availability, contradicting studies at coarser spatial scales. More basic taxonomic and floristic work is needed to help describe patterns of diversity for many groups to allow for testing the underlying mechanisms responsible for diversity gradients. in Spanish is available with online material. Resumen Explicar los patrones de riqueza de las especies es un tema central en la ecología. Se ha propuesto que las condiciones ambientales son los factores que generan estos patrones, sin embargo, aún debemos mejorar la comprensión de la contribución relativa de múltiples factores ambientales. En este trabajo, nuestro objetivo fue probar dos hipótesis ambientales para gradientes de riqueza: la disponibilidad de energía y la estacionalidad ambiental, utilizando el patrón de riqueza de la familia Leguminosae en México. Compilamos una base de datos de 502 especies y 32,962 registros. Posteriormente, dividimos a México en celdas de 100x100km, construimos un mapa de la variación de la riqueza de las especies que re