Species interactions and chemical stress: Combined effects of intraspecific and interspecific interactions and pyrene on Daphnia magna population dynamics

Species interactions are often overlooked when assessing the ecological impact of chemicals. However, they can greatly influence the way a population is affected by a chemical, either increasing or decreasing a chemical’s effects. In this publication, we examined three types of species interactions – intraspecific competition, interspecific competition and predation – in Daphnia magna populations exposed to pyrene. Predation and high initial intraspecific competition were shown to interact antagonistically with pyrene exposure i.e. the effect of pyrene was less pronounced. This was attributed to differences in population structure prior to pyrene exposure and pyrene-induced reductions in predation pressure. This study is a good example of how species interactions can alter the response of a population to chemical exposure in a way that cannot be predicted from single species tests alone.
 

Scientific abstract

Species interactions are often suggested as an important factor when assessing the effects of chemicals on higher levels of biological organization. Nevertheless, the contribution of intra- and interspecific interactions to chemical effects on populations is often overlooked. In the current study, Daphnia magna populations were initiated with different levels of intraspecific competition, interspecific competition and predation and exposed to pyrene pulses. Generalized linear models were used to test which of these factors significantly explained population size and structure at different time points. Pyrene had a negative effect on total population densities, with effects being more pronounced on smaller D. magna individuals. Among all species interactions tested, predation had the largest negative effect on population densities. Predation and high initial intraspecific competition were shown to interact antagonistically with pyrene exposure. This was attributed to differences in population structure prior to pyrene exposure and pyrene-induced reductions in predation pressure by Chaoborus sp. larvae. The current study provides empirical evidence that species interactions within and between populations can alter the response of aquatic populations to chemical exposure. Therefore, such interactions are important factors to be considered in ecological risk assessments.
 

Full reference (link)

Viaene KPJ, De Laender F, Rico A, Van den Brink PJ, Di Guardo A, Morselli M, Janssen CR. 2015. Species interactions and chemical stress: Combined effects of intraspecific and interspecific interactions and pyrene on Daphnia magna population dynamics. Environmental Toxicology and Chemistry, accepted article.
 

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