Understanding how ecological communities are assembled – the rules governing which species coexist in a given local area – has been a central theme in ecology for years. There have been a number of recent studies of various plant functional traits in the context of community assembly, but to our knowledge, this is the first to rigorously consider the role of leaf shape. While shape has been largely overlooked as a functional trait, it has been posited that shape may affect a leaf’s energy balance, the competitive effect of a tree on its smaller neighbors, as well as defense against herbivory. In this study, we ask three key questions: 1) Are tropical trees more or less variable in leaf shape overall than temperate trees? 2) Do leaves of given tropical forest tree species show more or less intraspecific variability than temperate species? 3) Do trees of different functional groups show different shape patterns or different levels of intraspecific variability across a latitudinal gradient?
To test these questions, we have sampled sun and shade leaves from eight individuals of a total of nine species across a latitudinal gradient. From a temperate forest in the Georgia Piedmont, a tropical dry forest in Belize, and a seasonal tropical moist forest in Panama, we selected a highly shade tolerant, an intermediate and a very shade intolerant species for analysis. Leaves were scanned, and images were analyzed using morphometric geometric software; multivariate statistical analyses were used to compare species and sites.
Results/Conclusions
There was a much higher degree of both inter- and intraspecific variability in leaf shape among all species in the temperate forest than in either tropical system. Species of intermediate shade tolerance tended to have the highest intraspecific plasticity, perhaps suggesting these species must be able to acclimate to the widest range of light environments. These patterns suggest a greater convergence of shared phenotypes in tropical forests and a greater variability and plasticity in species of temperate forests.
