Effects of diversity on colonization dynamics in newly formed ponds

Background/Question/Methods

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 which have indicated that an evolutionary focus can facilitate the explanation of observed patterns. Using temporary pond ecosystems as a model, we asked: (1) How does genetic and species diversity influence community assembly? (2) Does the diversity of ponds in a landscape (number of nearest neighbors) affect community assembly trajectories? (3) Does diversity influence average body size of a focal grazer (D. pulex). To test these questions, in Spring 2011, we stocked 28 newly constructed 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. Eleven ponds were left unstocked. Each pond was sampled twice a month starting from snow melt until the ponds dried in August for both 2011 and 2012.  Crustaceans were counted and identified to the lowest possible taxonomic unit, and body sizes were measured for D. pulex.  

Results/Conclusions

To date, we have recorded 25 species of crustacean zooplankton in our metacommunity with cumulative taxonomic richness ranging from 2 to 11 per pond. By the end of our second year, D. pulex had invaded 5 out of 11 control ponds and were undetectable in 7 out of 28 treatment ponds. Despite differences in initial stocking, by August 2012 the average number of taxa per pond did not differ significantly among any ponds (diversity treatments or control). Cyclopoids were rapid colonizers, and inhabited every pond by the first sampling period after the initial stocking (within two months). Daphnia, however, tend to be slower dispersers and colonized on average at 150 days in the 9 pond hexagons control ponds, 140 days in the 3 pond hexagon control ponds, and over 400 days in the isolated control ponds. Current results highlight the differential rates of dispersal among species in our metacommunity. Genetic and species diversity doesn't appear to have an effect on taxonomic richness, cumulative taxonomic diversity did not differ significantly. However, further analysis will be conducted to determine the spatial distribution of each species.