![]() Among them, the proportion of organisms able to cope with stress depends on each lineage's evolutionary context and the stressor historical persistence within the region. physiological, morphological and life-history adaptations conferring resistance to environmental stress) within the regional species pool. At a given stress level, abiotic filtering would select the organisms showing the most suitable response traits (i.e. Įmpirical and theoretical evidence suggests that abiotic filtering and interspecific competition are the most important mechanisms driving the predictable assembly of communities in response to environmental change (trait-filtering processes). However, it remains unclear whether anthropogenically modified stress levels would result in communities assembling along a single axis based on organisms' stress tolerance or along multiple trajectories of change depending on differential dispersal and colonization abilities and population dynamics. Chronic abiotic stress may arise naturally or be caused by ongoing global change, as occurs with fire disturbance frequency, flow intermittence or water salinity. This article is part of the theme issue ‘Salt in freshwaters: causes, ecological consequences and future prospects’.Ībiotic stress, defined as harmful environmental conditions exceeding the normal range experienced by organisms, is a key force determining how communities assemble and support ecosystem functions and services. The approach presented here provides both empirical and conceptual insights that can help in anticipating the ecological effects of global change, especially for those stressors with both natural and anthropogenic origins. Our findings suggest that the artificial modification of chemical stressors can result in different biological communities, depending on the direction of the change (salinization or dilution), with trait-filtering, and organism dispersal and colonization dynamics having differential roles in community assembly. Salinized rivers showed novel communities with different trait composition, while natural and diluted communities exhibited similar taxonomic and trait compositional patterns along the conductivity gradient. Our results showed that trait-filtering was important in driving community assembly in natural and diluted rivers, while dispersal-related processes seemed to play a relevant role in response to salinization. Here, we tested these hypotheses using aquatic macroinvertebrates from rivers exposed to gradients of natural salinity and artificially diluted or salinized ion contents. In response to stress intensity alterations, we hypothesize that a single trajectory of change occurs when trait-based assembly prevails, while multiple trajectories of change arise when dispersal-related processes modify colonization and trait-filtering dynamics. However, it remains unclear whether artificially increasing or decreasing stress levels would lead to communities assembling predictably along a single axis of variation or along multiple context-dependent trajectories of change. Abiotic stress shapes how communities assemble and support ecological functions.
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