EFFECTS OF DAPHNIA-LONGISPINA ON ROTIFER POPULATIONS IN A NATURAL-ENVIRONMENT - RELATIVE IMPORTANCE OF FOOD LIMITATION AND INTERFERENCE COMPETITION

To test the relative importance of exploitative and interference competition from Daphnia limiting rotifer populations in Bermejales reservoir, birth rates of rotifers, food abundance, zooplankton biomass and size distribution of Daphnia were analysed from high frequency sampling at two depths. A depletion in food abundance by Daphnia feeding should be reflected in the birth rates of rotifers susceptible to exploitative competition, while interference should produce direct negative relationships between the number of individuals of the interacting species. Results show that significant relationships between food (chlorophyll-a) and birth rates of rotifers are found when the ratio chlorophyll-a/herbivorous zooplankton biomass is used as a measure of food availability. In our study, Anuraeopsis fissa was only affected through exploitative competition by Daphnia, while only Synchaeta oblonga showed evidence of being suppressed through interference competition by this cladoceran.