Combined effects of food level and inoculation density on competition between brachionus patulus (rotifera) and the cladocerans ceriodaphnia dubia and moina macrocopa

摘要

Competition among cladocerans and rotifersis of considerable interest not only due to their close similarity in life history strategies,but also due to the considerable overlap they exhibit in their feeding habits.In tropical waterbodies,several genera of cladocerans,including Ceriodaphnia and Moina occur,simulataneously with rotifers.We tested over a period of 3 weeks hte combined effects of food (0.5*10~6 and 1.5*10~6 cells ml~(-1) of Chlorella) level and rotifer density on the competition between B.Patulus and C.dubia and M.macrocopa using population growth experiments.For each caldoceran species we used 30 test jars of 50 ml capacity.The initial density of cladocerans was 0.2 ind ml~(-1),while for B.patulus it was either 1 ind ml~(-1) or 5 ind ml~(-1).Neither the maximal population density nor the rate of populatin increase (r) of C.dubia was significantly affected by B.patulus.However,for M.macrocopa,both these variables were negatively affected by therotifers.The combined effects of low food level and high initial density of B.patulus resulted in a 50% reduction in the peak population density of M.macrocopa.The population growth of B.Patulus was negativley influenced by the presence of C.dubia and M.marrocopa.The results of the competition experiments conducted in the present study between cladocerans and rotifers suggest the existence of a more complex and delicate interaction thanis generally thought.