Unveiling patterns of taxonomic and functional diversities of stream insects across four spatial scales in the neotropical savanna

Abstract

The drivers of dissimilarity in biological communities among habitats and the mechanisms that modulate the distribution of functional diversity in streams are still important gaps in ecological knowledge. This study was designed to assess how the taxonomic and functional composition of Cerrado stream insect assemblages are distributed among multiple spatial scales (i.e., habitat, stream sites and hydrological units). To do so we used a hierarchical series of four diversity components: stream transect (α), among transects (β1), among stream sites (β2), and among hydrological units (β3). Our aim was to identify the spatial scales at which variation in aquatic insect assemblage structure was greatest and whether turnover or nestedness mainly explain the patterns of β-diversity. We found that β-diversity among streams (β2) is highest and contributes most to total richness (γ-diversity) of aquatic insects in Cerrado streams as opposed to dissimilarities among habitats or among hydrological units. Moreover, β-diversity among transects had the lowest contribution to total insect richness (γ-diversity). The turnover component of taxonomic β-diversity was high for all spatial scales, but highest at stream scale. Conversely, for functional β-diversity, nestedness was the main component at stream scale. Understanding how biodiversity changes from local to regional scales is a first step towards understanding the variation in species and trait composition across space. Our results emphasize the importance of conserving Cerrado headwater streams because each stream harbors different taxa and human disturbance of any stream will result in loss of diversity and ecosystem functions.