Response of zooplankton biodiversity to nutrient pulses in experimental mesocosms.

Abstract

Delineating the response of species to disturbance is a large part of ecological and environmental research. Freshwater ecosystems are essential for supporting life on earth and are also highly vulnerable to disturbance. With predicted increases in the intensity and frequency of disturbance associated with climate change understanding the impact of disturbance regimes on components of the ecosystem is important. The Intermediate Disturbance Hypothesis (IDH) predicts greater species diversity at a moderate intensity and frequency of disturbance than at a high intensity and frequency of disturbance. To test this postulate we assessed the response of zooplankton diversity to two nutrient pulse regimes; a moderate intense frequent pulse and a high intense infrequent pulse in four mesocosms. Higher zooplankton diversity was observed in the moderate intensity pulse in half the experimental group while higher zooplankton diversity was observed in the high intensity pulse. One-way ANOVA showed an effect of the nutrient pulse regime on chlorophyll a concentration but not on zooplankton diversity. Correlations between chlorophyll a concentration and zooplankton diversity were non-significant. The intermediate disturbance hypothesis may not account for zooplankton diversity within freshwater ecosystems. Alternative theories and mechanisms could better explain the trends in zooplankton diversity measured across experimental groups.