title: Chemical and natural stressors combined: from cryptic effects to population extinction.
abstract: In addition to natural stressors, populations are increasingly exposed to chemical pollutants released into the environment. We experimentally demonstrate the loss of resilience for Daphnia magna populations that are exposed to a combination of natural and chemical stressors even though effects on population size of a single stressor were cryptic, i.e. hard to detect statistically. Data on Daphnia population demography and along with model-based exploration of our predator-prey system revealed that direct trophic interactions changed the population size-structure and thereby increased population vulnerability to the toxicant which acts in a size selective manner. Moreover, population vulnerability to the toxicant increases with predator size and predation intensity whereas indirect trait-mediated interactions via predator kairomones may buffer chemical effects to a certain extent. Our study demonstrates that population size can be a poor endpoint for risk assessments of chemicals and that ignoring disturbance interactions can lead to severe underestimation of extinction risk.
authors.affiliation: Department of Environmental, Social and Spatial Change, Roskilde University, Universitetsvej 1, 4000 Roskilde, Denmark. gergs@ruc.dk
authors.forename: André
authors.initials: A
authors.lastname: Gergs
authors.forename: Armin
authors.initials: A
authors.lastname: Zenker
authors.forename: Volker
authors.initials: V
authors.lastname: Grimm
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Preuss