Stochastic processes and ecological connectivity drive stream invertebrate community responses to short‐term drought

Abstract

Community responses to and recovery from disturbances depend on local (e.g. presence of refuges) and regional (connectivity to recolonization sources) factors. Droughts are becoming more frequent in boreal regions, and are likely to constitute a severe disturbance for boreal stream communities where organisms largely lack adaptations to such hydrological extremes. We conducted an experiment in 24 semi‐natural stream flumes to assess the effects of local and regional factors on the responses of benthic invertebrate communities to a short‐term drought. We manipulated flow (drought vs. constant‐flow), spatial arrangement of leaf litter patches (aggregated vs. evenly distributed) and colonization from regional species pool (enhanced vs. ambient connectivity) to test the combined effects of disturbance, resource arrangement and connectivity on the structural and functional responses of benthic invertebrate communities. We found that a drought as short as 1 week reduced invertebrate taxonomic richness and abundance, mainly through stochastic extinctions. Such changes in richness were not reflected in functional diversity. This suggests that communities were characterized by a high degree of functional redundancy, which allowed maintenance of functional diversity despite species losses. Feeding groups responded differently to drought, with organic matter decomposers responding more than scrapers and predators. Three weeks were insufficient for complete invertebrate community recovery from drought. However, recovery was greater in channels subjected to enhanced connectivity, which increased taxonomic diversity and abundance of certain taxa. Spatial configuration of resources explained the least variation in our response variables, having a significant effect only on invertebrate abundance and evenness (both sampling occasions) and taxonomic richness (end of recovery period). Even a short drought, if occurring late in the season, may not allow communities to recover before the onset of winter, thus having a potentially long‐lasting effect on stream communities. For boreal headwaters, extreme dewatering poses a novel disturbance regime that may trigger substantial and potentially irreversible changes. An improved understanding of such changes is needed to underpin adaptive management strategies in these increasingly fragmented and disturbed ecosystems.

Climate and land‐use driven reorganisation of structure and function in river macroinvertebrate communities

“…Functional colonisations and extirpations showed weak or non-existent relationships with latitude (accepting our expectation E 1a but rejecting E 1b ). Discrepancies among spatial patterns of taxonomic and functional diversity in river macroinvertebrate communities have also been reported elsewhere (Crabot et al 2020, Sarremejane et al 2020. This may suggest that communities are characterized by different degrees of functional redundancy across the landscape, allowing maintenance of functional diversity despite species losses, which may have important implications for ecosystem functions and services (McLean et al 2019, Crabot et al 2020.…”

Climatic aridity increases temporal nestedness of invertebrate communities in naturally drying rivers

“…As human overallocation of freshwater resources interacts with climate change to cause more frequent and widespread drying (Prudhomme et al 2014), we need to anticipate how biodiversity will respond to novel drying disturbance across a range of climatic contexts. In systems in which river drying creates a novel disturbance regime, climate context may influence drying-induced compositional and functional changes in communities (Sarremejane et al 2020). However, our…”

Spatio‐temporal variation of macroinvertebrate metacommunity organization in a monsoon‐climate region

“…This finding suggests that stream macroinvertebrate metacommunity structure shows relatively low predictability. Future studies would benefit from considering additional potentially influential factors, such as climatic conditions, hydrologic properties, interspecific interactions and stochastic processes (Colzani et al, 2013;Sarremejane et al, 2021;Thompson et al, 2020). In addition, examining the performance of additional spatial distances (e.g.…”