Taxonomic and functional homogenisation of macroinvertebrate communities in recently intermittent Alpine watercourses

Abstract

1. Mountain streams are currently shifting from perennial to intermittent regime due to the combined effect of climate change and local anthropogenic pressures. Studies on the effect of flow intermittency on macroinvertebrates are as yet inconclusive due to the large heterogeneity in geographical areas and spatial scales at which this relationship has been investigated. Given that flow intermittency is a recently documented phenomenon in the Alps, only few studies have investigated functional and taxonomical diversity of benthic invertebrate communities in recently intermittent Alpine streams. 2. We used a hierarchical sampling design to investigate patterns in taxonomic and functional diversity of benthic invertebrate communities in 13 recently intermittent Alpine streams in NW-Italy. In each of these streams, we sampled in April 2017 benthic communities in two reaches with different hydrological conditions: a control reach, with permanent flow, and an intermittent reach, which recently experienced non-flow periods in summer. 3. We tested for the response of taxonomic richness at multiple spatial scales by partitioning total diversity into the average richness of local communities and the richness due to variation among local communities both within and among reaches. By partitioning total diversity (γ) into its local (α) and turnover (β) components we showed a decrease in local and regional species richness both within and among reaches, whereas variation among communities was significantly lower in intermittent reaches only at the reach scale. 4. The analysis of the multidimensional trait space of macroinvertebrates in reaches with different hydrological conditions further revealed a significant reduction of functional diversity, dispersion, and evenness in intermittent reaches. There was trait overdispersion in intermittent reaches, as these hosted both typical Alpine taxa and organisms adapted to flow intermittency. In particular, we observed the replacement of taxa with aquatic respiration and preferring medium-to fastflowing oligotrophic waters by taxa adapted to lentic habitats and with larval dormancy phases. 5. These results provide strong support that recent flow intermittency determines drastic changes of benthic invertebrate communities in Alpine streams which are facing a "mediterraneization" process. Our work highlights the importance of considering multiple spatial scales and of integrating taxonomic and functional diversity to throughly assess the impacts of flow intermittency.

Effects of experimental multi-season drought on abundance, richness, and beta diversity patterns in perennially flowing stream insect communities

“…Other studies of experimental flow reductions show that drought-affected communities shift toward more resilient smaller taxa with faster life cycles (Ledger et al, 2011;Aspin et al, 2018a), with strong dispersers replacing weak dispersers (Bogan et al, 2015), a higher proportion of lentic adapted taxa (Piano et al, 2020), and a shift in dominance toward generalists (Doretto et al, 2018). We did not find such pronounced shifts in taxonomic composition, and cursory examinations of traits yielded consistently low trait variation at all times of the study.…”

Assessment of ecological impairment of Arctic streams: Challenges and future directions

“…Indeed, functional diversity has been recognized as an important characteristic of biological communities (Mason et al., 2005). Biodiversity loss as a consequence of ecosystem deterioration can lead to structural changes in functional niche, eventually homogenizing trait composition within the community (Brown et al., 2018; Elias et al., 2015; Piano et al., 2020). The functional aspects of recovery could be used in biomonitoring by comparing predictable changes in functional diversity along environmental gradients as well as comparing co‐occurring groups (Berger et al., 2018; Cai et al., 2019; Menezes et al., 2010; Van den Brink et al., 2011).…”

Accounting for flow intermittence in freshwater species distribution modelling

“…Background locations, also called pseudoabsences, are locations where presence/absence of the species is unknown, representing the range of environmental conditions in the study area. To account for potential spatial bias in species presence data due to unequal sampling effort, while providing accurate representation of environmental variations in the study area, we followed the recommendations of Barbet-Massin et al (2012) and Phillips and Dudík (2008). We selected a set of 10,000 background stream reaches in the study area, excluding the stream reaches where the Pyrenean brook newt presence is known.…”

“…We selected a set of 10,000 background stream reaches in the study area, excluding the stream reaches where the Pyrenean brook newt presence is known. Both background data and species occurrence records were thus biased in the same manner (Phillips & Dudík, 2008). However, the spatial bias in sampling is expected to be low, as Pottier et al (2021) suggested that the current distribution of the Pyrenean brook newt in France is now relatively well known due to huge sampling efforts since the 1990s.…”

“…We ran MaxEnt in logistic format to get an estimation of the probability of presence, given the environmental conditions (Phillips & Dudík, 2008), and we used quadratic feature type to approach unimodal species response to environmental variables (Austin, 2007).…”