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

Abstract

Climate change is altering the water cycle globally, increasing the frequency and magnitude of floods and droughts. An outstanding question is whether biodiversity responses to hydrological disturbance depend on background climatic context -and if so, which contexts increase vulnerability to disturbance. Answering this question requires comparison of organismal responses across environmental gradients. However, opportunities to track disturbed communities against an undisturbed baseline remain rare. Here we gathered a global dataset capturing responses of aquatic invertebrate communities to river drying, which includes 112 sites spanning a gradient of climatic aridity. We measured the effects of river drying on taxonomic richness and temporal β-diversity (turnover and nestedness components). We also measured the relative abundance of aquatic invertebrates with strategies that confer resilience (or resistance) to drying. Contrary to our expectations, we found that taxonomic richness recovered from drying similarly across the aridity gradient. The turnover component of β-diversity (i.e. species replacements over time) largely accounted for differences in community composition before versus after drying. However, increasing aridity was associated with greater nestedness-driven compositional changes at intermittent sites -that is, after drying communities became subsets of those before drying. These results show that climatic context can explain variation in community responses to the same hydrological disturbance (drying), and suggest that increased aridity will constrain biodiversity responses at regional scales. Further consideration of the climatic context in hydroecological research may help improve predictions of the local impacts of hydrological disturbance by identifying climate regions where communities are more (or less) sensitive to extremes, including river drying events.

Alpha and beta diversity and species co‐occurrence patterns in headwaters supporting rare intermittent‐stream specialists

“…Indeed, with mounting interest in the biogeographic and climatic context‐dependency of drying impacts spurring more and more meta‐analyses (e.g. Leigh & Datry, 2017; Sabater et al., 2018; Vander Vorste et al., 2021), there is a clear need for standardised diversity metrics that allow for robust comparisons across studies.…”

Lack of congruence between fundamental and realised aridity niche in a lineage of water beetles

“…It is well known that coping with increasing aridity is a physiological challenge for all organisms (Chown et al., 2011). Aridity influences biodiversity at multiple levels, shaping species distributions at fine and large geographical scales (Craine et al., 2013; Rajpurohit et al., 2013; Watling & Braga, 2015), driving lineages diversification (Catullo & Keogh, 2014; Dorn et al., 2014; Pinceel et al., 2013; Razeng et al., 2017) and community turnover (Vander Vorste et al., 2021), and regulating ecosystem structure and function (Berdugo et al., 2020).…”

The Drying Regimes of Non‐Perennial Rivers and Streams

“…These five hydrologic signatures have been directly or indirectly linked to a stream's ecological, biological, and chemical patterns and processes (Costigan et al, 2015(Costigan et al, , 2017Naiman et al, 2008;Poff et al, 1997). For example, dry-down duration, drying rate, and no-flow start date have ecological consequences for mobile aquatic species that may relocate in drying periods (Rosset et al, 2017), no flow duration is critical for the survivability of species that have certain streambed moisture saturation thresholds (Vorste et al, 2021), and antecedent peak quantile may influence pre-drying hydrologic connectivity conditions such as floodplain connectivity that may provide cascading ecological implications (Penha et al, 2017).…”

“…streams that experience rapid seasonal disconnect with contributing flowpaths, such as groundwater (Fig- ures 1 and S3). These seasonal similarities and differences in cluster membership undoubtedly reflect the unique influence that each drying regime may impart on ecosystem processes, such as habitat partitioning (Crabot et al, 2020), organic matter processing (Harjung et al, 2019), and community structure (Vorste et al, 2021).…”

“…From this, we may be able to apply similar water resources or ecosystem management strategies to specific streams or at certain times of year. For example, it has been shown that the duration of drying is a key variable influencing biodiversity in non-perennial streams (Datry, Larned, Fritz, et al, 2014) and the rate at which drying occurs also affects the degree to which aquatic taxa are able to migrate elsewhere and persist during no-flow conditions (Vorste et al, 2021). Therefore, we anticipate aquatic taxa maybe more diverse and have higher survival rates in the cluster 3 drying regime with longer drying duration, and may require less conservation interventions during periods that are dominated by cluster 1 events, which display rapid drying.…”