Functional diversity quantifies the value and range of organismal traits that influence species performance and contribution to ecosystem functioning. Functional diversity (rather than simply taxonomic diversity) provides a mechanistic framework to understand community productivity and resilience to perturbations or invasion. Aquatic insect functional diversity using multidimensional metrics has been examined in the past decade, but not in the context of strong environmental gradients. We applied a multifaceted framework to quantify three primary components of functional diversity of stream insects along an elevation gradient. We used Functional Richness (FRic), Functional Evenness (FEve) and Functional Divergence (FDiv) indices to test for significant differences in aquatic insect functional diversity in 24 small streams in three adjacent catchments, spanning an elevational range of ca. 2000–3500 m.
Our results showed that only FRic differs significantly with elevation, and that the pattern of change remains constant across catchments. Our findings provide independent information concerning position and relative abundances of species in a multidimensional functional space, and they allow for inferences on elevational patterns of aquatic insect functional beta diversity in mountain streams.