Species that are phylogenetically similar may exhibit functionally equivalent effects on the structure and function of their ecosystems. Diaptomus copepods are differentiated on the basis of their sexual traits, but little is known about the ecological differences among species. Recent work using stable isotope and shape analysis has revealed possible ecological differences among species that could affect the functioning of aquatic ecosystems. In the current study, we experimentally test whether species and populations of Diaptomus differentially affect the structure of aquatic food webs and the rates of biomass production, decomposition, and export.

Results/Conclusions

We found that three species (Leptodiaptomus ashlandi, Hesperodiaptomus franciscanus, Skistodiaptomus oregonensis) had similar effects on rates of primary productivity and decomposition, but different effects on rates of sedimentation, and on algal biomass and nutrient cycling. Generally, populations of the same species had similar effects on ecosystem functioning, but in some cases bacteria biomass differed among populations. Overall, the identity of the dominant copepod species influenced the export of organic matter to sediments, the abundance of primary producers, and the cycling of nutrients. This suggests that phylogenetically similar species can exhibit potentially cryptic effects on the structure and functioning of ecosystems.