Print PageIntraspecific diversity, like interspecific diversity, potentially affects ecosystem function, including productivity and nutrient dynamics. Genetic richness of dominant or keystone species is predicted to be particularly important for predator-prey and consumer-resource dynamics. While most studies focus on the intraspecific diversity of producers, our goal was to determine the effects of genotypic richness of a primary consumer on ecosystem function. Daphnia, a keystone species in freshwater ecosystems, is an intermediary consumer that plays a critical role in trophic cascades. In lakes, a single species of Daphnia often dominates the water column, making it an ideal organism with which to test the effects of intraspecific diversity on ecosystem function. We conducted a mesocosm experiment manipulating genotypic richness of Daphnia (1, 2, 4, and 8 clones) and monitored consumer-resource dynamics (algae and Daphnia) and ecosystem function (nutrient availability and oxygen production/consumption). In addition, we used microsatellites to measure genetic diversity in the middle and at the end of the experiment to determine which clones were the best competitors.
Results/Conclusions
Intraspecific diversity of Daphnia clearly affected algae and Daphnia population dynamics. Across monocultures, interclonal differences resulted in variation in the height and timing of peaks in algae and Daphnia densities. As Daphnia genotypic richness increased (2, 4, and 8 clone treatments), maximum algal biovolume generally decreased, indicating that consumer genetic diversity impacts consumer-resource interaction strength. This resulted in different rates of oxygen production and consumption, suggesting that intraspecific diversity of this keystone species also affects ecosystem function. Across diversity treatments, some clones emerged as superior competitors, indicating that clonal identity was also important. Microsatellite analysis identified differences in genotype frequencies in the middle and at the end of the experiment: some clones present at the midpoint disappeared by the end. This is likely the result of decreased algal densities due to increased Daphnia biomass in the second half of the experiment, suggesting that food quantity played a role in regulating clonal dynamics. The results of this experiment indicate that i) intraspecific diversity of consumers has the potential to affect consumer-resource dynamics and ecosystem function, and ii) genotypic identity likely plays a key role in the maintenance of genetic diversity in clonal populations.
