Predicting the effects of pollution at the community level is difficult because of the complex impacts of ecosystem dynamics and properties. To predict the effects of copper on a plant-herbivore interaction in a freshwater ecosystem, we built a model that focuses on the interaction between an alga, Scenedesmus sp., and a herbivore, Daphnia sp. The model assumes logistic growth for Scenedesmus and a type II functional response for Daphnia. Internal copper concentrations in Scenedesmus and Daphnia are calculated using a biodynamic model. We include two types of direct effects of copper on Scenedesmus and Daphnia that results from hormesis: a deficiency effect at low concentration and a toxic effect at high concentration. We perform a numerical analysis to predict the combined effects of copper and nutrient enrichment on the Scenedesmus-Daphnia interaction. Results show three types of outcomes depending on copper concentration. First, low (4 μg L(-1)) and high (50 μg L(-1)) copper concentrations cause deficiency and toxicity, respectively, leading to the extinction of all populations; for less extreme concentrations (between 4 and 5 μg L(-1) and between 16.5 and 50 μg L(-1)), only the consumer population becomes extinct. The two populations survive with intermediate concentrations. Second, when population dynamics present oscillations, copper has a stabilizing effect and reduces or suppresses oscillations. Third, copper, on account of its stabilizing effect, opposes the destabilizing effect of nutrient enrichment. Our model shows that (1) Daphnia is affected by copper at lower concentrations when community interactions are taken into account than when analyzed alone, and (2) counterintuitive effects may arise from the interaction between copper pollution and nutrient enrichment. Our model also suggests that single-value parameters such as NOEC and LOEC, which do not take community interactions into account to characterize pollutants effects, are unable to determine pollutant effects in complex ecosystems. More generally, our model underscores the importance of ecosystem-scale studies to predict the effects of pollutants.

Although there is an increasing interest in the effects of anthropogenic noise on animals, aquatic studies mainly focus on organisms with hearing systems (marine mammals, fish, great arthropods) while many others of substantial ecological importance are not considered. Here we show that the water flea Daphnia magna, a widespread zooplankton species serving as food source for higher trophic levels, could be affected by noise pollution in a way that we did not expect. We found that isolated individuals exposed to a continuous broadband sound have a higher survival and fecundity, thus a higher fitness. We also found that they are slower than individuals not exposed to additional noise. It could be that the energy saved from reduced mobility is reallocated to fitness. In natural systems, this reduced velocity should result in a more negative outcome for Daphnia's fitness due to competition and predation. Our result highlights that, despite the absence of a known hearing system, a small crustacean can be affected by noise. Consequently, anthropogenic noise can not only affect communities through top-down cascading effects, when it changes the behaviour of top-predators like fish, but also via bottom-up effects with alterations in zooplankton.

1-Parasites are important components of food webs. Although their direct effects on hosts are well-studied, indirect impacts on trophic networks, thus on non-host species, remain unclear. 20 2-In this study, we investigate the consequences of parasitism on coexistence and stability within a simple trophic module: one predator consuming two prey species in competition. We test how such effects depend on the infected species (prey or predator). We account for two effects of parasitism: the virulence effect (parasites affect the infected species intrinsic growth rate through direct effects on fecundity or mortality) and the interaction effect (increased 25 vulnerability of infected prey or increased food intake of infected predators).3-Results show that coexistence is favored when effects have intermediate intensity. We link this result to modifications of direct and apparent competitions among prey species.Given a prey infection, accounting for susceptible-infected population structure highlights that coexistence may also be reduced due to predator-parasite competition. 30 4-Parasites affect stability by modulating energy transfer from prey to predator. Predator infection therefore has a stabilizing effect due to increased energy fluxes and/or predator mortality. 5-Our results suggest that parasites potentially increase species coexistence. Precise predictions however require an assessment of various parasite effects. We discuss the 35 implications of our results for the functioning of trophic networks and the evolution of foraging strategies within food webs.3 Keyword: apparent competition, direct competition, host-parasite interaction, interaction effect, paradox of enrichment, prey-predator interaction, stability, virulence 40 4

Parasites are omnipresent, and their eco-evolutionary significance has aroused much interest from scientists. Parasites may affect their hosts in many ways by altering host density, vulnerability to predation, and energy content, thus maximizing profitability within the optimal foraging framework. Consequently, parasites could impact predator diet and trophic links within food webs. Here, we investigate the consequences of the iridovirus Daphnia iridescent virus 1 (DIV-1) infection on the reproductive success, mortality, appearance, mobility, and biochemical composition of water fleas (Daphnia magna), a widespread freshwater crustacean. We compare search time between infected and uninfected Daphnia preyed by a common aquatic insect (Notonecta sp.) as well as the handling time and feeding preference of Notonecta sp. Our findings show that infection does not change fecundity but reduces lifespan and thereby constrains fitness. Infected Daphnia show reduced mobility and increased color reflectance in the UV and visible domains, which potentially affects their visibility and thus catchability. Infection increases body size and the amount of proteins but does not affect carbohydrate and lipid contents. Although infected Daphnia had a longer handling time, they tended to be preferred over uninfected individuals by aquatic insects. Taken together, our findings show that DIV-1 infection could make Daphnia more profitable to predators (23% energy increase), a positive effect that should be balanced with density reductions due to higher mortalities. We also highlight that exposure to infection in asymptomatic individuals leads to ecological characteristics that differ from both healthy and symptomatic infected individuals.

There is a growing interest in the effects of noise pollution on marine ecosystems. To date, these works mainly focus on hearing species, especially fish and mammals. Because these species are generally at the upper trophic levels, key species from lower levels, like zooplankton species, are less studied under noise effects. Zooplankton is already used as bioindicators, to understand fluxes, ecological dynamics and global change effects; however, it remains a lack of knowledge on the effect of noise. Previous works demonstrate that they could detect vibrations. Consequently, noise is susceptible to affect the perception of their environment and to induce stress. Combining their short life cycle, their phylogenetic and ecological diversity, zooplankton could be useful organisms to understand a diversity of noise effects. They can be used to study the effects at individual scales as modifications of physiology, development, and behavior. Responses, that could change species interactions and population dynamics, are expected to lead to larger scale implications (i.e., alterations of food webs dynamics and ecosystem functioning). Here, we bring out, from studies in ecology, ecotoxicology, and parasitology, methods that can be adapted to our current questions. We might expect further development of acoustic studies on zooplankton, in order to better apprehend how anthropogenic noises affect marine environments.

Article Keyword: Adaptive foraging, virulence, vulnerability, predator diet, profitability, parasitism Running title: Prey-infection induce diet evolution Number of words: 4 470 List of elements: Article (23p) with 1 table and 5 figures. Appendix (4p) with 2 figures. AbstractAs acknowledged by Optimal Foraging theories, predator diets depend on prey profitability.Parasites, ubiquitous in food webs, are known to affect simultaneously host vulnerability to predation and host energy contents, thereby affecting profitabilities. In this work, we study the eco-evolutionary consequences of prey infection on predator diet. We also analyze the consequences for coexistence between prey, predators and parasites. We model a trophic module with one predator and two prey species, one of these prey being infected by a parasite, and distinguish between two effects of infection: a decrease in host fecundity (virulence effect) and an increase in vulnerability to predation (interaction effect). Predator foraging may evolve toward specialist or generalist strategies, the latter being less efficient on a given resource. We show that the virulence effect leads to specialisation on the non-infected prey while the interaction effect, by increasing prey profitability, favors specialisation on the infected prey.Combining the two effects at intermediate intensities promotes either generalist predators or the diversification of foraging strategies (coexistence of specialists), depending of trade-off shape. We then investigate how the evolution of predator diet affects the niche overlap between predator and parasite. We show that interaction effects systematically lead to a high niche overlap, ultimately resulting in the loss of the parasite. Virulence effects conversely favor coexistence by allowing a separation of the predator and parasite niches.

Parasites are important components of food webs. Although their direct effects on hosts are well-studied, indirect impacts on trophic networks, thus on non-host species, remain unclear. In this study, we investigate the consequences of parasitism on coexistence and stability within a simple trophic module: one predator consuming two prey species in competition. We test how such effects depend on the infected species (prey or predator). We account for two effects of parasitism: the virulence effect (parasites affect the infected species intrinsic growth rate through direct effects on fecundity or mortality) and the interaction effect (increased vulnerability of infected prey or increased food intake of infected predators). Results show that coexistence is favored when effects have intermediate intensity. We link this result to modifications of direct and apparent competitions among prey species. Given a prey infection, accounting for susceptible-infected population structure highlights that coexistence may also be reduced due to predator-parasite competition. Parasites affect stability by modulating energy transfer from prey to predator. Predator infection therefore has a stabilizing effect due to increased energy fluxes and/or predator mortality. Our results suggest that parasites potentially increase species coexistence. Precise predictions however require an assessment of various parasite effects. We discuss the implications of our results for the functioning of trophic networks.

Ecotoxicological studies mainly focus on chemical pollution, however, since past decades, there has been a growing interest for the acoustic pollution. Previous studies on underwater acoustic pollution showed that noise affects vertebrates' behaviour, like fish and marine mammals. However, little is known about other organisms. Consequently, we studied important lacking aspects, well known with chemical pollution: the effect on a key zooplankton species (used as bioindicator) and the effect on fitness (survival and fecundity). We exposed isolated water fleas, Daphnia magna, to chronic boat noise or to a silence broadcasted as control, from birth to death. We measured effects on lifespan and clonal offspring production (e.g., clutch size, number of produced offspring along life). We did not observe any effect of the chronic boat noise exposition on Daphnia's fitness. These results are consistent with results on previous acute noise exposure, but also opposite to other ones found with acute and chronic noise effect. Thus, we discuss how the noise structure and temporal pattern could affect its impacts on aquatic organisms. Our work highlights that noise pollution should be integrated in ecotoxicological studies, but also that some particular aspects of this pollutant should be considered differently than chemical pollutants.