Effects of drying and orientation to perennial refuges on aquatic biodiversity across two basins differing in aridity

Abstract

Intermittent streams are globally distributed, comprise over half the length of the global river network, and are expected to become more prevalent. However, most studies of intermittent streams are conducted at extremes of scale, are limited in taxonomic and temporal scope, and focus exclusively on drying patterns. Here, we assessed how both flow intermittency and orientation to perennial refuges affect aquatic invertebrates and aquatic and semiaquatic vertebrates across 2 years within two intermittent river basins differing in their aridity. We used loggers to characterize flow intermittency and wet-dry mapping to determine orientation to perennial refuges of reaches. In winter and summer 2015 and 2016, we collected and identified invertebrates and visually surveyed vertebrates. Using permutational multivariate analyses of variance with distance matrices, we found distinct invertebrate communities by basin, flow class (perennial or intermittent), and season, and distinct vertebrate communities by basin, and between flow classes and seasons in the more arid basin. Invertebrate communities had higher beta diversity in the more arid than mesic basin, whereas the opposite was true for vertebrates. We identified indicator species for all combinations of basin and flow class, perennial reaches combined from both basins, each basin, and some combinations of flow class and season within basins. Flow intermittency and orientation to perennial refuge predictors correlated well with both invertebrate and vertebrate communities. However, we did not find nestedness of communities that differed significantly from that expected by chance in response to increasing flow intermittency or distance to refuges. Lastly, basin, flow intermittency, and orientation to perennial refuge predictors were generally important for modeling taxon richness and densities, and richness and densities decreased with increasing flow intermittency and distance to perennial refuges. Collectively, our data suggest that intermittent streams harbor unique biodiversity, but also that some taxa have context-dependent responses to intermittency and orientation to perennial refuges. These findings also suggest that future

Effects of stream drying, season, and distance to refuge on macroinvertebrate community structure in an arid intermittent stream basin

“…In contrast, intermittency did not appear to strongly influence macroinvertebrate taxonomic composition. Previous studies have found support for both distinct communities with unique taxa in intermittent reaches (e.g., Bogan et al, 2013; Gill et al, 2022) and intermittent communities that were merely nested subsets of those found in perennial reaches (e.g., Bonada et al, 2007; Vander Vorste et al, 2021). However, the level to which some taxa were identified in previous studies could impact the level of taxonomic distinctness that is detected between intermittent and perennial reaches.…”

“…The spatial configuration of perennial and intermittent reaches within a stream network can vary across networks and regions and influence biodiversity as well (Gill et al, 2022; Sarremejane et al, 2020). In mesic regions, flow intermittency is typically found only in the headwaters (Fritz et al, 2013), whereas in arid regions, it can occur at any point within the watershed (Acuña et al, 2014).…”

“…Recolonization of these isolated habitats would be reliant on taxa that are strong active fliers or those that can drift from upstream refuges if flow connects for long enough (Bogan et al, 2017). Distance to the nearest perennial refuges may determine how quickly these reaches can be recolonized and whether high biodiversity can be sustained within the reach (Gill et al, 2022; Robson et al, 2011).…”

Coleoptera associated with intermittent streams and their riparian zones in south coastal British Columbia

“…Studies done to date on intermittent stream biodiversity have primarily focused on aquatic species ( e.g. , Valente-Neto et al 2020; Bunting et al 2021; Gill et al 2022), but patterns of drying affect riparian communities as well, particularly terrestrial invertebrates (Corti and Datry 2014; Sánchez-Montoya et al 2016, 2020). Many riparian invertebrates rely on aquatic invertebrates as prey, pursuing them either by swimming or by burrowing into the substrate to extract them (Hering 1998; Paetzold et al 2005).…”

“…Stream drying can promote high species turnover in stream and associated riparian invertebrate communities both directly, based on water availability, and indirectly, by providing habitat for migration and additional sources of nutrients for consumption (Larned et al 2010). Studies done to date on intermittent stream biodiversity have primarily focused on aquatic species (e.g., Valente-Neto et al 2020;Bunting et al 2021;Gill et al 2022), but patterns of drying affect riparian communities as well, particularly terrestrial invertebrates (Corti and Datry 2014;Sánchez-Montoya et al 2016. Many riparian invertebrates rely on aquatic invertebrates as prey, pursuing them either by swimming or by burrowing into the substrate to extract them (Hering 1998;Paetzold et al 2005).…”