Species diversity within and among Daphnia assemblages in newly established lakes

Background/Question/Methods

Metacommunity and evolutionary theory predict that dispersal and gene flow will homogenize diversity within and among communities, whereas ecological sorting and local adaptation will differentiate it.  Here we study species and phenotypic diversity of Daphnia assemblages in lakes created recently (within the last 80 years), located within a small geographic area occurring in Kickapoo State Park.  In 2003-2007, we compared Daphnia species composition within and among eight lakes in our study area.  In May 2007, we asked how genetic and phenotypic diversity were distributed across the five lakes in which both Daphnia pulicaria and Daphnia dentifera co-occur.  We assayed the variation in adult body size and fecundity in field-collected adults and raised multiple clonal lines from all 10 populations in the laboratory under high food.

Results/Conclusions

The relative abundances of Daphnia species differed among lakes.  These differences cannot be attributed to limited dispersal ability because sediment cores reveal that all species have colonized each study lake since their inceptions.  Instead, differences in community composition can be attributed to ecological sorting along a gradient in fish predation, representing well established ecological trade-offs among species related to body size.  Thus, although dispersal does not limit species colonization, it is not high enough to overwhelm ecological sorting.    From our laboratory experiment in May 2007, we found that, as with the species diversity, gene flow is not high enough to homogenize phenotypic diversity within species of Daphnia among lakes.  In addition, microsatellite markers revealed low to moderate, but significant, genetic differentiation among lakes (Fst).