Estimation of inter- intraspecific variation across scales
We used variance partitioning among two factors (Ribas et al. 2006) to estimate the relative contribution of inter- vs. intraspecific trait variation at the continental scale by comparing each model (phylogenetic and environmental) to the combined model following Munoz & Real (2006). The idea of using variance partitioning to understand intra- vs inter-specific trait variation was originally developed by de Bello et al. (2011; see also Leps et al. 2006), but this work focused on estimating variance from field data in the absence of a model. We use the traditional approach from statistics by quantifying the proportion of variance attributable to purely phylogenetic drivers (σ2Phylo = R2comined – R2Env), purely environmental drivers (σ2Env = R2comined – R2Phylo), and the proportion that is jointly shared between them (σ2joint = R2comined – σ2Phylo – σ2Env).
To quantify the relative effects of environment, species and phylogeny on inter- and intraspecific trait variation at the regional scale (eastern US), we used the combined model to estimate the leaf traits for all individual trees in the FIA data.