Landscape variables influence taxonomic and trait composition of insect assemblages in Neotropical savanna streams

Stream invertebrate assemblages are structured by environmental factors acting at multiple spatial scales. Identifying the spatial scale that most influences the species-environment relationships is a major goal of community ecology. We evaluated the importance of catchment and site scales and associated environmental variables in shaping Ephemeroptera, Plecoptera and Trichoptera (EPT) assemblages in Neotropical savanna headwater streams. Sampling sites were associated with 20 catchment-scale variables that depicted land cover and land use as well as natural geophysical variables such as altitude and climate. Site-scale habitat was characterised by 55 variables that described habitat hydromorphology, substrate, flow, canopy, in-stream cover and water quality. EPT traits were assessed using 28 categories of 7 biological traits, which represented the best available current knowledge for EPT in Neotropical savanna streams. We analysed the relationships between the catchment- and site-scale habitat variables and the taxonomic and trait composition of insect assemblages using 1,760 samples collected in 160 stream sites. Catchment- and site-scale variables both explained significant variation in EPT taxon and trait composition. Substrate, habitat hydromorphology and land use most influenced variation in taxonomic composition, whereas trait composition was mainly affected by land use. Catchment geographic position explained less assemblage variation. To our knowledge, this study is the first assessment of the impact of catchment- and site-scale variables on the trait and taxon composition of stream insect assemblages in Neotropical savanna streams. It highlights the need for better regional biological knowledge of invertebrates to generate more general trait-based approaches in freshwater ecosystem conservation.