Size?dependent sensitivity of stream amphipods indicates population?level responses to chemical pollution

Global change assessments have typically ignored synthetic chemical pollution, despite the rapid increase of pharmaceuticals, pesticides, and industrial chemicals in environment. The paucity research on ecological effects these micropollutants undermines our efforts to address freshwater biodiversity crisis. Understanding responses individual organisms pollution should help this knowledge gap because individual-level can cascade across populations, communities, ecosystems with devastating consequences. Inputs treated municipal wastewater are a major source receiving environments. Here, we assessed population influences gammarid amphipods (Gammarus spp.) Swiss lowland streams situ tested micropollutant mixture Gammarus fossarum using common garden laboratory experiment. We hypothesised that population-level mediated through asymmetric sensitivities juvenile adult gammarids pollutants. expected life-stage specific would reflect allometric theory relating body size wide range organismal characteristics, including metabolism, growth, mortality. At level (i.e. field survey), observed greatly reduced abundances downstream discharge three six sites surveyed, indicating potential for demographic pollution. transplant experiment, found presence led steeper positive relationship between leaf consumption. In had negative consumption growth rates, but effect survival. Differences performance were subtle treatments, although flatter slopes appear be consistent response Faster rates appeared connected survival, placing individuals control treatments and/or smaller at greatest risk Notably, faster lower survival than adults when exposed micropollutants. Our results demonstrate impacts ecosystems. However, also show pollutants complex, whereby may act counter-intuitively dynamics. This highlights need more realistic experiments better assess how depend life stage size, propagate higher levels biological organisation. study shows used examine stressors underlying biology, demographics, link broader macroecological patterns.