Abstract

Anthropogenically induced environmental changes (e.g. global warming, eutrophication) are ranked among the major drivers of biodiversity loss in different types of ecosystems. In aquatic ecosystems, herbivorous zooplankton feeds directly on phytoplankton (primary producers). Thus, changes in the biodiversity of phytoplankton might alter the zooplankton community structure. While there have been numerous laboratory experiments that examined the impact of biodiversity on ecosystem functioning and community dynamics, it is not known whether the patterns observed at small scales also occur in complex natural communities. To examine such patterns in “wild nature”, we conducted large-scale experiments in three Bavarian lakes along a trophic gradient (oligotrophic to eutrophic). We manipulated the natural phytoplankton communities of the lakes through manipulation of the water column stratification at different frequencies. We first hypothesized that the disturbance of the water column stratification leads to a loss of stress sensitive phytoplankton species and thus changes the biodiversity of the natural phytoplankton community. As a consequence, the zooplankton community composition could also change due to trophic cascades. Our results show that disturbance altered not only phytoplankton community composition (determined as changes in the pigment composition of the algal community), but also affected the consumer trophic level (microcrustacean zooplankton) through an alteration of the relative dominance of cladoceran and copepod microcustaceans.

Dr. Maja Ilić

Data Analyst/R Programmer in Ecology