Evolutionary metacommunity theory is a promising conceptual framework for integrating community ecology and evolution to understand the distribution of diversity. This theory builds on the increasing number of empirical studies of community assembly that have indicated that an evolutionary focus can facilitate the explanation of observed patterns. Using temporary pond ecosystems as a model, the questions we address are: (1) To what extent do species interactions versus dispersal limitation influence community assembly? (2) How does genetic diversity influence community assembly? To test these questions, in Spring 2011, we stocked 28 newly constructed temporary ponds with one of four treatments: (1) One genotype of Daphnia pulex, no regional zooplankton, (2) Six genotypes of D. pulex, no regional zooplankton, (3) One genotype of D. pulex with regional zooplankton (4) Six genotypes of D. pulex with regional zooplankton. Ten ponds were left unstocked, allowing us to quantify colonization via unaided dispersal. Each pond was sampled twice a month starting from the snow melt in 2011 until the ponds dried in August. Crustacean and rotifer species were counted and identified to the lowest possible taxonomic unit, and body sizes (which correlate with birth and death rates) were measured for D. pulex.
Results/Conclusions
To date, we have recorded eight species of crustacean zooplankton and six species of rotifers in our metacommunity. By the end of the season, D. pulex had invaded seven control ponds, and was absent from seven of the 28 treatment ponds. Daphnia densities in most control ponds remained < 2 / L, whereas in the treatment ponds, Daphnia densities as high as 200 / L were recorded. In many August samples, the Daphnia population was dominated by juveniles, resulting in average body sizes in these populations typically being < 1 mm, whereas populations in which adults were abundant typically had a mean body size > 1.2 mm. Cyclopoid copepods were found in all ponds, with densities ranging over three orders of magnitude. The highest densities were reached in the control ponds indicating that cyclopoids were able to both disperse to and establish in these ponds. However, as the result of the among-pond variation, we found no difference between population densities of cyclopoids in control vs. treatment ponds in August. Continued sampling and analysis of similarities and differences in community structure among treatments will help elucidate the role of genetic and species diversity in determining community assembly and species coexistence.