COMPARATIVE FEEDING ECOLOGY OF TROPOCYCLOPS-PRASINUS-MEXICANUS (COPEPODA, CYCLOPOIDA)

The herbivorous and carnivorous feeding biology of Tropocyclops prasinus mexicanus, an especially small cyclopoid copepod, was studied under in situ food conditions in three different lakes and under experimentally augmented food supplies. The mass-specific food uptake is compared to that of two larger species-Cyclops kolensis and Cyclops vicinus. Under in situ food conditions, T.p.mexicanus depended to a larger extent on algae than invertebrate prey and showed lower mass-specific ingestion rates than the two larger species. Daily mass-specific uptake rates for algae ranged between 10 and 24% of its body mass versus 0.7-7% for invertebrate prey. The larger species C.vicinus and C.kolensis ingested a total dry mass equivalent to 106% or up to 143% of their body mass with algae contributing 66 and 81%. However, under enriched food availability, Tp.mexicanus is able to ingest a biomass equivalent to its body mass, with an algae (54%) and prey (40%) portion similar to that of the larger species. Body size appears to be an important factor for the relative importance of algal versus invertebrate prey for cyclopoid copepods.