Abstract
Rivers are heterogeneous and patchy-structured systems in which regional biodiversity of aquatic communities typically varies as a function of local habitat conditions and spatial gradients. Understanding which environmental and spatial constraints shape the diversity and composition of benthic communities is therefore a pivotal challenge for basic and applied research in river ecology. In this study, benthic invertebrates were collected from 27 sites across three hydro-ecoregions with the aim of investigating patterns in α- and β diversity. We first assessed the contribution to regional biodiversity of different and nested spatial scales, ranging from micro-habitat to hydro-ecoregion. Then, we tested differences in α diversity, taxonomic composition and ecological uniqueness among hydro-ecoregions. Variance partitioning analysis was used to evaluate the mechanistic effects of environmental and spatial variables on the composition of macroinvertebrate communities. Macroinvertebrate diversity was significantly affected by all the spatial scales, with a differential contribution according to the type of metric. Sampling site was the spatial scale that mostly contributed to the total richness, while the micro-habitat level explained the largest proportion of variance in Shannon–Wiener index. We found significant differences in the taxonomic composition, with 39 invertebrate families significantly associated with one or two hydro-ecoregions. However, effects of environmental and spatial controls were context dependent, indicating that the mechanisms that promote beta diversity probably differ among hydro-ecoregions. Evidence for species sorting, due to natural areas and stream order, was observed for macroinvertebrate communities in alpine streams, while spatial and land-use variables played a weak role in other geographical contexts.
Highlights
Biodiversity, which is commonly defined as the variety of life forms that live in a certain habitat (Colwell 2009), is a key definition in community ecology with direct applications for basic and applied research
Lotic ecosystems are highly heterogeneous and patchy-structured habitats in which regional biodiversity of benthic communities is expected to vary according to both local environmental conditions and spatial gradients
When the relative abundance of benthic invertebrates was taken into consideration by using the Shannon-Wiener index, we found an opposite trend
Summary
Biodiversity, which is commonly defined as the variety of life forms (e.g. species or taxa) that live in a certain habitat (Colwell 2009), is a key definition in community ecology with direct applications for basic and applied research. Decomposing the regional diversity into its a and b components appears advantageous for heterogeneous and hierarchically structured systems, like rivers, where data are usually collected at multiple and nested spatial scales, such as micro-habitats, river stretches and basins (Ward and Tockner 2001; Tornwall et al 2015; Er}os and Lowe 2019) In addition to these natural levels of organization, there are anthropogenic levels—transects (Piano et al 2017), meso-habitats (Burgazzi et al 2017) and hydroecoregions (Li et al 2001)—originated for biomonitoring purposes, including the standardization of sampling procedures and comparison between observed and expected community metrics (Bo et al.2017)
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