DOI: 10.5061/dryad.w3r2280mj
title: Data from: Size-dependent sensitivity of stream amphipods indicates population-level responses to chemical pollution

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