Verbose community analysis results. from Biological interactions mediate context and species-specific sensitivities to salinity

Toxicants have both sub-lethal and lethal effects on aquatic biota, influencing organism fitness and community composition. However, toxicant effects within ecosystems may be altered by interactions with abiotic and biotic ecosystem components, including biological interactions. Collectively this generates the potential for toxicant sensitivity to be highly context dependent, with significantly different outcomes in ecosystems than laboratory toxicity tests predict. We experimentally manipulated stream macroinvertebrate communities in 32 mesocosms to examine how communities from a low-salinity site were influenced by interactions with those from a high-salinity site across a gradient of salinity. Relative to those from the low-salinity site, organisms from the high-salinity site were expected to have greater tolerance and fitness at higher salinities. This created the potential for both salinity and tolerant-sensitive organism interactions to influence communities. We found that community composition was influenced by both direct toxicity and tolerant-sensitive organism interactions. Taxon and context-dependent responses included: (i) direct toxicity effects, irrespective of biotic interactions; (ii) effects that were owing to the addition of tolerant taxa, irrespective of salinity; (iii) toxicity dependent on sensitive-tolerant taxa interactions; and (iv) toxic effects which that were increased by interactions. Our results reinforce that ecological processes require consideration when examining toxicant effects within ecosystems.This article is part of the theme issue ‘Salt in freshwaters: causes, ecological consequences and future prospects’.有毒污染物对水生生物群落兼具亚致死与致死效应，可影响生物体适合度与群落组成。然而，生态系统内的毒物效应可能因与非生物、生物生态组分（包括生物相互作用）的交互作用发生改变。综合来看，这使得毒物敏感性呈现极强的情境依赖性，且生态系统中的实际效应与实验室毒性试验的预测结果存在显著差异。我们在32个中型实验生态系统（mesocosms）中对溪流大型无脊椎动物群落开展了实验操控，旨在探究低盐位点的群落如何沿盐度梯度受到高盐位点群落的交互影响。相较于低盐位点的生物体，高盐位点的生物体在高盐环境下本应具备更强的耐受性与适合度，这使得盐度作用与耐受-敏感生物交互作用均有可能对群落产生影响。研究发现，群落组成同时受到直接毒性与耐受-敏感生物交互作用的影响。类群与情境依赖的响应包括：(i) 不受生物相互作用影响的直接毒性效应；(ii) 仅因引入耐受类群而产生的效应，与盐度无关；(iii) 依赖于敏感-耐受类群交互作用的毒性效应；以及(iv) 因交互作用而增强的毒性效应。本研究结果证实，在探究生态系统内的毒物效应时，需充分考量生态过程的作用。本文隶属于《淡水盐度：成因、生态后果与未来展望》专题议题。