Drought alters the functional stability of stream invertebrate communities through time

Abstract

Aim:In fresh waters, most biogeographical understanding of how extreme events such as drought modify biodiversity and ecosystem functioning derives from static, spatial comparisons of ecological communities, between intact and disturbed sites or along stress gradients. Impacts of drought on the development of ecological communities over time remain poorly resolved, with information on parallel trends in community structure and function particularly scarce. In theory, drought could progressively eliminate both species and functional traits, rendering communities increasingly taxonomically and functionally nested subsets of their pre-existing counterparts. Alternatively, drought could create new niche opportunities, producing a continuous turnover of species and traits, or simply constrain natural community succession.Location: Dorset, UK.Taxon: Aquatic invertebrates. Methods:We studied temporal changes in community structure and function in artificial streams over 2 years, comparing drought (frequent drying) with control (constant flow) conditions. Temporal beta diversity was partitioned into turnover and nestedness components, calculated using both presence-absence and abundance data, and analysed using time-lag and null modelling approaches. Results: Community development was comparable taxonomically under control anddrought conditions, driven primarily by temporal turnover of species. Under control conditions, corresponding trends in functional composition were not apparent, and species turnover was characterized by the progressive replacement of some species by others of equivalent abundance. By contrast, species turnover in disturbed communities was accompanied by both functional turnover and greater loss of individuals, indicating that new colonists were not equivalent, either functionally or numerically, to those they replaced. Furthermore, functional dissimilarities between time points were greatest under drought, and more similar in magnitude to taxonomic dissimilarities, implying that drying reduced the stability and redundancy of functional attributes. | 1989LEIGH Et aL.

Drying determines the temporal dynamics of stream invertebrate structural and functional beta diversity

“…When a significant effect was found for the associated mixed model, a line was plotted with the intercept and slope estimated in the model. with finer temporal resolutions are scarce (but see Leigh et al 2019), we gained a better understanding of how drying influences biodiversity patterns by including the temporal and spatial dynamics of drying. Our results underline some limits of current biomonitoring methods in IRs and offer refined avenues to better target sites for conservation prioritization.…”

“…Although beta diversity, defined as the extent of change in community composition between localities or occasions (Anderson et al 2011), can provide valuable insights into the relationship between local and regional patterns of biodiversity and their underlying processes (Socolar et al 2016, Aspin et al 2018, it remains poorly quantified in highly dynamic ecosystems, particularly with respect to its temporal dynamics (Datry et al 2016, Sarremejane et al 2017a, Leigh et al 2019. Moreover, the partitioning of beta diversity into two additive components, replacement (taxa replacement between two localities) and richness difference (difference in the number of taxa), can add substantial information on how communities differ (Podani andSchmera 2011, Cardoso et al 2014).…”

How freshwater biomonitoring tools vary sub‐seasonally reflects temporary river flow regimes

“…This study identified strong sub‐seasonal (monthly) variations in biomonitoring tools associated with channel drying events and the resumption of flowing conditions in both case studies. Ecological responses to flow cessation events in riverine environments are often tested through seasonal sampling programmes and/or space‐for‐time substitution designs (e.g., control versus impact; Leigh et al, ). Studies and biomonitoring programmes adopting such practices may overlook community transformations occurring over time as species are gained or lost, and the biotic interactions that stem from this which alter the temporal trajectories of riverine ecosystems Bogan et al, ; Leigh et al, ).…”

“…Ecological responses to flow cessation events in riverine environments are often tested through seasonal sampling programmes and/or space‐for‐time substitution designs (e.g., control versus impact; Leigh et al, ). Studies and biomonitoring programmes adopting such practices may overlook community transformations occurring over time as species are gained or lost, and the biotic interactions that stem from this which alter the temporal trajectories of riverine ecosystems Bogan et al, ; Leigh et al, ). This study reinforces the value of adopting sub‐seasonal sampling strategies within temporary rivers in order to understand ecological responses to the cessation and resumption of flowing conditions at time scales more in keeping with the temporal dynamics of ecosystem responses.…”

“…Studies examining the ecological structure and functioning of temporary rivers, as well as biomonitoring tools specifically, have typically adopted seasonally targeted sampling programmes (e.g., García‐Roger et al, ; Cid et al, ; Garcia, Gibbins, Pardo, & Batalla, ; Wilding et al, ). However, such sampling strategies may not adequately capture temporal trajectories of ecological change occurring within or between different seasons, such as the rapid recolonization of taxa and biological transformations occurring following the resumption of flowing conditions (e.g., Bogan, Boersma, & Lytle, ; Ledger & Hildrew, ; Leigh, Aspin, Matthews, Rolls, & Ledger, ) or multiple flow cessation events occurring intra‐annually (e.g., Hill & Milner, ; Stubbington et al, ). As such, ecological responses and changes to biomonitoring tool scores associated with flow regime variations in temporary rivers may not be adequately captured by traditional seasonal sampling strategies.…”