Assessing the impact of dispersal on zooplankton community structure

The prevalence of metacommunity models in recent ecological research has illustrated the importance of dispersal in the maintenance of regional biodiversity.  Species dispersal, however, has the potential to interfere with species interactions and influence local community structure, as has been well documented in the growing literature on exotic species invasion.  In this study, we attempted to quantify the impact of dispersal on zooplankton community structure using a freshwater mesoocosm experiment.  Specifically, we sought to identify whether there was a threshold level of dispersal below which community structure would remain unchanged by dispersing species. To do so, we collected plankton communities differing both in species richness and community structure from three lakes in the Eastern Townships of Quebec and housed them separately in eighty-litre mesocosms.  We established seven experimental treatments representing different magnitudes of dispersal, ranging from 0-10% total volume.  Mixing events occurred twice over the course of the 12 week experiment whereby a set volume was extracted from each of the three communities per treatment and mixed together before it was returned to the mesocosms.  We used NMDS ordination to group communities according to their population abundance structure and found that dispersal magnitudes of less than 1% of total volume were insufficient to homogenize the structure of three initially disparate communities over the 3 month experimental period.