Abstract
Temporary rivers (TRs) dominate global river networks and are increasing in occurrence and spatiotemporal extent. However, few studies have investigated the communities that establish after rewetting events (i.e. the end of the dry phase), when local hydrological conditions can shape the communities through species sorting, and the spatial connectivity of sites can also influence colonisation. Here, we analysed the relative importance of both local hydrological conditions and spatial connectivity on the invertebrate communities of seven not impacted Mediterranean TRs after rewetting. We quantified the frequency and duration of drying events and the time since flow resumed. We also quantified spatial connectivity based on each site’s position in the river network (i.e. network connectivity) and the presence of nearby disconnected streams. Overall, we found that both hydrological conditions and network connectivity played a significant role in structuring aquatic invertebrate communities after rewetting. Taxonomic richness, functional richness and functional redundancy decreased with the frequency and duration of drying events and increased with time since the most recent rewetting. Network connectivity showed a significant unimodal relationship with taxonomic and functional metrics. In contrast, the presence of nearby disconnected streams was negatively related to functional richness and functional dispersion. Given that flow intermittence in Mediterranean areas is expected to intensify under future global change scenarios, our results can be helpful to guide future conservation and management actions.
Highlights
IntroductionRiver ecosystems that recurrently cease to flow or dry up at some point in time and space (i.e. temporary rivers, Temporary rivers (TRs)) occupy more than 50% of the global river network (Messager et al, 2021) and they are becoming more abundant due to global change (Doll & Schmied, 2012; Sauquet et al, 2021)
River ecosystems that recurrently cease to flow or dry up at some point in time and space occupy more than 50% of the global river network (Messager et al, 2021) and they are becoming more abundant due to global change (Doll & Schmied, 2012; Sauquet et al, 2021)
Flow intermittence varied along a gradient between \ 1% to 66% across the seven Temporary rivers (TRs) (Fig. 1b), being highest at SC2 (66%; total duration of drying events (TotDur): 339 days; TotNum: 25 events), and lowest at MU4 (0.2%; TotDur: 1 day; TotNum: 1 event)
Summary
River ecosystems that recurrently cease to flow or dry up at some point in time and space (i.e. temporary rivers, TRs) occupy more than 50% of the global river network (Messager et al, 2021) and they are becoming more abundant due to global change (Doll & Schmied, 2012; Sauquet et al, 2021). TRs are common in Mediterranean climates (Bonada & Resh, 2013; Cid et al, 2017) where they experience seasonal and predictable floods and droughts (McElravy et al, 1989; Gasith & Resh, 1999) These ecosystems fluctuate between two main periods: dry and wet, in which TRs experience different hydrological conditions (Gallart et al, 2012; Bonada et al, 2020). TRs dry up or have disconnected pools that can persist throughout the summer, whereas during the wet period TRs flow and instream habitats include both riffles and pools These changing instream conditions impose a strong environmental filter that directly controls the taxonomic and functional composition of invertebrate communities (Williams, 2006; Gallart et al, 2012). In Mediterranean river catchments that are fed Hydrobiologia by surface runoff, flow resumption is typically triggered by increased precipitation and runoff in the headwaters, which is sometimes intense enough to cause flash floods that swiftly transform channels from completely dry to flowing strongly (Jacobson et al, 2000; Cohen & Laronne, 2005)
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