Seasonality, species richness and poor dispersion mediate intraspecific trait variability in stonefly community responses along an elevational gradient

Abstract

Summary Across environmental gradients, some functional strategies are favoured over others resulting in differences in local species composition and distribution of any given functional trait. This generates among‐Species Trait Variability (STV) across the gradient (reflecting species turnover), as well as spatial Intraspecific Trait Variability (ITV), which together contribute to Community Trait Variability (CTV). Understanding functional trait responses of freshwater biota is critical for elucidating the mechanisms that operate during community assembly and addressing community level responses to climate warming. In freshwater insects, temperature and ecological conditions regulate growth rates. Here, we examined size‐related trait variability components of short‐dispersing stoneflies (Insecta: Plecoptera) within and among multispecies stonefly assemblages (henceforth referred to as communities), located along an elevational gradient in Sierra Nevada (Spain) to assess the components of trait‐elevation matching (STV, ITV, CTV). Relative to downstream reaches, headwaters hypothetically show greater internal physical habitat heterogeneity (large exposed rocks, tree roots, woody debris) and greater local species richness of cool‐water adapted stoneflies. As a result, we expected CTV to increase with elevation, with a higher contribution of STV than ITV in upper reaches due to higher species richness and trait divergence among them. In contrast, the pattern of ITV should vary depending on whether the main driver across elevation is species richness (decrease due to niche partitioning) or ecological conditions (increase associated to physical habitat heterogeneity). Eleven streams were sampled every 2 weeks over 1 year and five size‐related traits were measured on 6,893 individuals belonging to 16 species. Overall, STV made a much larger contribution to CTV than ITV, which only became an important contributor in species‐poor assemblages, especially in winter and autumn. Within each season, the trait‐elevation matching was weak. Functional species‐specific responses to the elevational gradient most often did not mirror the response of the entire communities, since highly variable (and even opposed or discontinuous) contributions to ITV were found across species. Overall, ITV contributed little to trait‐elevation matching, which suggests high vulnerability of short‐dispersing stoneflies to habitat shifting associated to future climate warming due to limited phenotypic plasticity. Moreover, varying functional trait patterns across species emphasise species‐specific responses to climate change as opposed to a unique whole community response. However, further trait‐based macroecological studies across freshwater macroinvertebrates lineages are needed to compare patterns and establish generalisations.

Demographic modelling reveals a history of divergence with gene flow for a glacially tied stonefly in a changing post‐Pleistocene landscape

“…With the addition of genomic data, demographic model testing unequivocally favoured a history of gene flow over models that either excluded migration fully, or included fewer migration parameters. Both morphological (Garcia‐Raventós, Viza, Tierno de Figueroa, Riera, & Múrria, ) and mtDNA (Finn & Adler, ; Finn, Encalada, & Hampel, ; Giersch et al., ; Jordan et al., ) evidence suggests that stoneflies (and related alpine stream species) are poor dispersers. Consequently, the support for gene flow occurring on large spatial scales is surprising and may provide some degree of optimism from a climate change perspective.…”

Getting chased up the mountain: High elevation may limit performance and fitness characters in a montane insect

“…Montane species may be uniquely sensitive to these forces because the climate is changing rapidly at high altitude (Pepin et al, ). As many montane species are already living on the edge of both suitable habitat and physiological tolerance, small environmental changes may result in large changes in survival, performance or reproductive success (Garcia‐Raventos, Viza, De Figueroa, Riera, & Murria, ; MacLean, Higgins, Buckley, & Kingsolver, ; Shah et al, ; Stewart, Wright, & Heckman, ). The ability of organisms to persist in the face of novel conditions requires traits that allow them to move or adapt to new conditions in situ (Buckley & Bridle, ; Lancaster, Dudaniec, Hansson, & Svensson, ).…”

Stochasticity overrides deterministic processes in structuring macroinvertebrate communities in a plateau aquatic system

“…The fate of many organisms in a changing environment depends on their ability to track the shifting environmental conditions by migration and/or by local adaptation (Lin et al 2017). Hence, the ongoing climate warming may result in significant changes in the distribution, abundance, population dynamics, and ecophysiological responses of organisms, including the responses by many freshwater macroinvertebrates (Garcia‐Raventos et al 2017, Heino et al 2020). As we showed in this study, acknowledging the relative influences of deterministic and stochastic processes on variation in different dimensions of ecological communities is highly important for understanding global change impacts on biodiversity maintenance and ecosystem dynamics in the Anthropocene.…”