OMNIVORY IN CYCLOPOID COPEPODS - COMPARISONS OF ALGAE AND INVERTEBRATES AS FOOD FOR 3, DIFFERENTLY SIZED SPECIES

We examined the importance of algal versus invertebrate prey for three cyclopoid copepods by comparing reproductive success for females fed on three diets: exclusively algal food, exclusively invertebrate prey and a combination of algal plus invertebrate prey. The three cyclopoid species represent a distinct gradient in body size: Tropocyclops prasinus mexicanus (small body size), Diacyclops thomasi (medium body size) and Mesocyclops edax (large body size). Our results provide strong evidence for the potential importance of algae in the diet of adult cyclopoid copepods. However, the role of herbivory is dependent on species body size. We found that algae are the key dietary factor for reproductive success of the small T.p.mexicanus. In contrast, the availability of invertebrate prey had a greater influence on reproduction by the two larger species. Overall, cyclopoid copepods should be generally considered as having the potential to derive their energy from either animal or algal sources. This has important consequences for interpretations of the forces influencing zooplankton community diversity as well as for general food web theory.