Do all roads lead to Rome? Exploring community trajectories in response to anthropogenic salinization and dilution of rivers

Abstract

Abiotic stress shapes how communities assemble and support ecological functions. 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. 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. Here, we tested these hypotheses using aquatic macroinvertebrates from rivers exposed to gradients of natural salinity and artificially diluted or salinized ion contents. 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. 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 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. 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. This article is part of the theme issue ‘Salt in freshwaters: causes, ecological consequences and future prospects’.

How Does Mining Salinisation Gradient Affect the Structure and Functioning of Macroinvertebrate Communities?

“…To date, the impact of salinisation on benthic fauna has chiefly been studied only in running waters (e.g. Piscart et al 2005a, b;Velasco et al 2006;Kefford et al 2011;Piscart et al 2011;Schäfer et al 2011;Cañedo-Argüelles et al 2014Golovatyuk and Shitikov 2016;Gutiérrez-Cánovas et al 2019a;Laceby et al 2019;. Data on salinisation in anthropogenic water bodies is relatively rare (Williams 2001;Blasius and Merritt 2002).…”

Effects of salinity changes on aquatic organisms in a multiple stressor context

“…Non-additive effects are reflected by a deviation from the additive response, which can be greater (synergism) or less (antagonism) than the sum of individual effects [13] and thus exacerbate or mitigate, respectively, the effects on organism performance [14]. These changes at organism level are the primary and most sensitive responses to stress [15] but may ultimately alter community composition [16] and interfere with ecosystem processes and services, which sustain human welfare [17]. In recent years, several meta-analyses have synthesized the results of studies that have tested joint effects of multiple stressors in marine [12,18,19] and freshwater ecosystems [20] at different organizational levels, from organisms to communities, and have shown contrasting results.…”

Multiple co‐occurrent alien invaders constrain aquatic biodiversity in rivers

“…The functional characteristics of the communities were characterized using biological traits describing life history, resilience or resistance features, reproduction strategy, respiration, feeding preferences and feeding mode according to Tachet et al (2010) and Schmidt-Kloiber and Hering (2015) at the genus level. This taxonomic level is widely utilised in research focussed on functional diversity and the response of riverine communities to external stressors (Gutiérrez-Cánovas et al 2019). The entire dataset of biological traits was used to derive FRich while 5 "effect traits" (size, dispersal, mode of locomotion, food consumed and feeding habits) were used to calculate FRed, following the approach used for alpine and temperate riverine communities previously (Bruno et al 2019, Laini et al 2019).…”