Disturbance,competition and the maintenance of clonal diversity in Daphnia pulex

Laboratory microcosm experiments tested the intermediate disturbance hypothesis, which states that the highest level of diversity (e.g. species diversity) will be maintained at intermediate scales of disturbance. The effects of disturbance on the maintenance of clonal diversity and on competitive interactions among clones of the obligately parthenogenetic freshwater cladoceran, Daphnia pulex were examined. No significant effect of disturbance size (i.e. dilution volume) on clonal diversity was noted. However, frequency of disturbance had a pronounced effect on clonal diversity, with the highest clonal diversity maintained at low to intermediate disturbance frequencies. Competitive hierarchies among clones were often invariant within a given experiment. Generally, one or two clones dominated, with several less abundant clones persisting throughout an experiment. Results suggest that low to intermediate disturbances could be important in the maintenance of genetic variation in natural populations (i.e. through pre-emption of competitive exclusion between genotypes). This could have a direct bearing on the maintenance of both intra- and interspecific diversity.