Influence of Phenotypic Plasticity in Photosynthetic Functions on the Spatial Distributions of Tropical Trees

The services that tropical rain forests provide and the roles they play in harboring much of the world's terrestrial biodiversity are widely appreciated. There is worldwide concern about the consequences of human activities on these services. Knowledge of the role of plant function in shaping biogeographical distributions of trees contributes to efforts to preserve, restore, and manage these forests. Recognition is growing that plasticity in the expression of functions by a given genotype and not just genotypic specialization may play an adaptive role in shaping spatial distributions of species. Their structure and life history characteristics make trees among the most likely candidates for higher levels of plasticity in functional phenotype of all plant forms. Moreover, many tropical areas meet theoretical expectations for the environmental heterogeneity that may favor selection for phenotypic plasticity. Trees are, however, generally avoided in tests of the adaptiveness of levels of phenotypic plasticity for particular ranges of environments. I emphasize a need to quantify specific photosynthetic and water use functions that are fundamental bases for fitness and outline some avenues to achieve these measurements on tree species. Tests of the adaptiveness of levels of plasticity in phenotype remain more elusive. I present the case, however, that tests of correlation between levels of plasticity in functions of species and quantified parameters of their geographies can generate knowledge of what combinations of species can co-occur in a given landscape.