Contrasting taxonomical and functional responses of stream invertebrates across space and time in a Neotropical basin

Abstract

The structure of the EPT group (Ephemeroptera, Plecoptera and Trichoptera) reflects changes operating on the underlying freshwater system. We study the structure of the EPT assemblages inhabiting a Neotropical basin with mountain rain forests. Taxonomic richness and functional diversity are two relevant indicators of that structure. We measured real biological traits rather than using trait classifications arising from the Northern hemisphere, allowing us to more accurately calculate functional diversity metrics in these Neotropical streams. We also formalized a new approach to measuring functional dissimilarity. Our main scope is to know the effects of space (altitudinal zonation) and time (seasonality) on the behavior of both diversity indexes. We find complementarities between them, suggesting that the replacement in taxonomic composition is a process decoupled from the replacement in trait composition. While the taxonomic richness of sites in the dry season differs from the richness in upland sites sampled during spates, the functional diversity allows us to differentiate lowland sites sampled during spates from other sites. We hypothesize that functional diversity goes down in lowland sites because of the anthropogenic pressure on the riparian area. We additionally stress that the knowledge of functional diversity contributes to the better design of conservation strategies.