PS 5-62 - Functional biogeography of Caribbean tropical dry forests

Abstract: Tropical dry forests are among the most fragmented habitat type in the tropics. The Caribbean, a biodiversity hotspot, contains nearly 10% of the world’s tropical dry forests, yet are relatively understudied. Recent work showed that remnant Caribbean tropical dry forests that harbor high plant endemism are geographically structured and dispersal-limited. However, plant functional variation and its relationship with the highly variable climate across tropical dry forests in the Caribbean is not well studied. Precipitation seasonality defines tropical dry forests and the gradient of precipitation seasonality within Caribbean dry forests should lead to diverse plant form and function. In addition, island size (and potentially dry forest area) is a known driver of species diversity, yet the impacts of area on trait variation is less well known. To examine these ideas, we quantified plant trait variation and determined their climatic and biogeographic drivers across Caribbean dry forests. We used an existing database of 572 woody vegetation plots spanning 11 archipelagos across the Caribbean, including Florida. We then extracted seed mass, specific leaf area, and wood density from global trait databases. We supplemented additional seed mass data from herbaria collections and completed a phylogenetic imputation of traits. We then calculated presence-absence community weighted means and functional diversity and correlated these metrics with bioclimatic variables in addition to island area and dry forest area for each island using generalized additive models. Our results indicate that, despite occurring in climatically distinct regions, Caribbean tropical dry forests are functionally similar and the trait space of many dry forests are nested within the functional space of others. We also showed that island or dry forest area were uncorrelated with functional diversity and temperature and precipitation seasonality were the strongest determinants of trait variation and functional diversity. Thus, in more variable climates, functional diversity was greater. We discuss these findings in light of methodological limitations, and suggest that finer trait sampling is likely to reveal even stronger underlying interactions between functional trait variation and climate in these highly seasonal and highly variable Caribbean tropical dry forests.