The importance of retaining a phylogenetic perspective in traits-based community analyses

Many environmental stressors manifest their effects via physiological processes (traits) that can differ significantly among species and species groups. We compiled available data for three traits related to the bioconcentration of the toxic metal cadmium (Cd) from 42 species representing the aquatic insect orders Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies). These traits included the propensity to take up Cd from water (uptake rate constant, k(u)), the ability to excrete Cd (efflux rate constant, k(e)) and the net result of these two processes (bioconcentration factor). Ranges in these Cd bioaccumulation traits varied in magnitude across clades (some clades had a greater tendency to bioaccumulate Cd than others). Overlap in the ranges of trait values among different clades was common and highlights situations where species from different lineages can share a similar trait state, but represent the high end of possible physiological values for one clade and the low end for another. Variance around the mean trait states differed widely across clades, suggesting that some groups (e.g. Ephemerellidae) are inherently more variable than others (e.g. Perlidae). Thus, trait variability/lability is at least partially a function of lineage. Akaike information criterion comparisons of statistical models were more often driven by lineage than by the other tested potential biological or ecological explanations. Lineage-driven models generally improved with increasing taxonomic resolution. Together, these findings suggest that lineage provides context for the analysis of species traits and that failure to consider lineage in community-based analysis of traits may obscure important patterns of species responses to environmental change.