Intraspecific Trait Variation in Tree Species Responds to Environmental Heterogeneity at Range-Wide but Not Local Scales.

Theoretical and empirical ecology have recently explored the role of intraspecific trait variation (ITV) in structuring ecological communities. Such trait variation may be correlated with high environmental variability within a site or across a species' range. Here we explore the relationship between ITV, spatial and temporal environmental heterogeneity, and the breadth of species' environmental distributions for 33 tree species across eight sites occurring along marked environmental gradients in Puerto Rico. Specifically, we asked (1) If within-site ITV is positively correlated with site-level temporal and spatial environmental variation, and (2) How across-site ITV relates to the breadth of species' environmental distributions on the island. Two key plant traits, leaf mass per area (LMA) and wood density, were used to understand the association between ITV and environmental variation. We examined ITV across species and sites using statistical models to assess the relationship between (1) within-site ITV and site-level spatial (topography) and temporal (rainfall) environmental variability; (2) across-site ITV and environmental variation across the species geographic range on the island. We also assessed the relationship between across-site mean trait values and island-wide environmental ranges. (1) Across all species, we did not find any significant associations between within-site ITV and site-level temporal or spatial variability. (2) Greater ITV values of LMA and wood density were associated with larger environmental ranges. We also found that species with high wood density, a trait associated with a conservative growth strategy, had narrower ranges across climatic conditions, but this pattern was not evident for LMA. Our findings emphasize the complexity of the relationships between ITV and species distributions with respect to environmental heterogeneity at different spatial and temporal scales. These complexities are important for research on species distributions and range-shift dynamics.