Disentangling the effects of streamflow permanence and land use on the β‐diversity of Odonata assemblages in the Pampa grasslands

Abstract Changes in streamflow permanence regime and in land use intensity surrounding streams can greatly affect the distribution of aquatic insects and the ecosystem services that they provide. However, hydrological variation may alter land use impacts on aquatic insect assemblages. Therefore, untangling the effects of flow permanence and landscape composition on β‐diversity is key to predicting the effects of land use and climate change on aquatic insect assemblages, especially in modified biomes such as the South American subtropical grasslands (Pampa). Here, we surveyed the composition of Odonata assemblages in low‐order streams differing in their flow permanence and type of land cover to test whether st reamflow permanence and landscape composition drive Odonata β‐diversity patterns in the Brazilian Pampa. Specifically, we assessed the extent to which β‐diversity replacement and nestedness components vary between historically ‘perennial’ (with continuous flow all year‐round) and ‘intermittent’ streams (which dry part of the year) along a gradient of anthropogenic land cover. Flow permanence and anthropogenically impacted land cover independently influenced overall β‐diversity (and the turnover component), while anthropogenic land cover alone influenced the nestedness component. These findings suggest that intermittent flow in the stream channel throughout the year and landscape encroachment lead to the filtering out of flow‐sensitive Odonata and favour drought‐adapted taxa, while natural land use favours the occurrence of specialist taxa in Pampa streams. This study helps disentangle the mechanisms structuring the distribution of Odonata along gradients of hydrological permanence and land use in southern Brazilian grassland streams. These results are useful to predict the responses of Odonata biodiversity to streamflow regime change in landscapes under increasing environmental pressure and water surface loss.