| Rotifers and cladocerans are important constituents and dominant groups offreshwater zooplankton communities. Interspecific competition between rotifers andcladocerans is one of major driving forces regulating structure and constituent of aquaticecosystem. In this thesis, the competitive outcomes between Brachionus calyciflorus or B.angularis and Moina macrocopa with different body sizes, exploitative competitiveabilities and defensive mechanical interference abilities were investigated at differenttemperatures, algal food levels and rotifer initial densities, and the effect of interspecificcompetition on the life history characteristics of the rotifers and the cladoceran wasstudied using population growth experiments and life table techniques. Chemicalinterference between each of two rotifer species and the cladoceran, and threshold foodconcentration and starvation ability of the three species of zooplankton were compared.The results of these researches will help us further understand the competitive mechanismsbetween rotifers and cladocerans, and distinguish correctly the relative importance amongexploitative competition, mechanical interference competition and chemical interferencecompetition under different competitive environments. The main contents and results werepresented as following:1. The competitive outcomes between B. calyciflorus or B. angularis and M.macrocopa were investigated at different temperatures (20℃,25℃and30℃), algal fooddensities (0.5,1.0and3.0×106cells/ml Scenedesmus obliquus) and rotifer initial densities(2,4and6ind./ml of B. calyciflorus, and1,3and5ind./ml of B. angularis). The resultsshowed that the competitive outcomes between B. calyciflorus and M. macrocopa weredependent on algal density but not temperature and rotifer initial density. Regardless oftemperature and rotifer initial density, M. macrocopa outcompeted B. calyciflorus at thelowest algal density (0.5×106cells/ml), while B. calyciflorus outcompeted M. macrocopaat the higher algal densities (1.0and3.0×106cells/ml). The competitive outcomes betweenB. angularis and M. macrocopa were dependent on algal density, temperature and rotifer initial density. B. angularis and M. macrocopa coexisted, except that M. macrocopaoutcompeted rapidly B. angularis at30℃and the higher algal densities (1.0×106and3.0×106cells/ml) under rotifer initial density of3ind./ml during7to10days. Thedifferent competitive outcomes between B. calyciflorus or B. angularis and M. macrocopamight be attributed to their differences in adaptative abilities to different temperatures andfood densities, and the differences in body size, exploitative competitive ability anddefensive mechanical interference ability of the two rotifer species. Generally,interspecific competition between the two rotifer species and M. macrocopa decreasedtheir population densities. However, when M. macrocopa excluded or coexisted with thetwo rotifer species, the two rotifer species increased M. macrocopa population densities,which might be attributed to the chemical interference interaction between B. calyciflorusor B. angularis and M. macrocopa.2. The effects of interspecific competition between B. calyciflorus or B. angularis andM. macrocopa on their life history characteristics were studied at different temperatures(20℃,25℃and30℃), algal food densities (0.5,1.0and3.0×106cells/ml S. obliquus) andM. macrocopa competitive strengths (1,3and5ind./5ml). The results of three-wayANOVAs showed that the competition of M. macrocopa decreased the life tabledemographic parameters such as intrinsic rate of population growth of the two rotiferspecies. The competition of B. calyciflorus stimulated the reproduction of M. macrocopaand increased the number of offspring produced in her life. Conversely, the competition ofB. angularis inhibited the reproduction of M. macrocopa and decreased the number ofoffspring produced in her life. The different effects of interspecific competition betweenthe two rotifer species and M. macrocopa on their life history parameters might beattributed to their adaptative differences to temperature and food density, and thedifferences in body size, exploitative competitive ability and defensive mechanicalinterference ability of the two rotifer species and chemical interference interactionbetween B. calyciflorus or B. angularis and M. macrocopa. It partially explained that M.macrocopa excluded B. clyciflorus and B. angularis coexisted with M. macrocopa.3. The effects of chemical interference interaction between B. calyciflorus or B.angularis and M. macrocopa on their life history characteristics were investigated atdifferent temperatures (20℃,25℃and30℃), algal food densities (0.5,1.0and3.0×106cells/ml S. obliquus) and the three zooplanktons species-conditioned medium (0,50%and 100%). The results of three-way ANOVAs showed that M. macrocopa-conditionedmedium did not affect life history parameters including intrinsic rate of population growthof B. calyciflorus, but decreased those of B. angularis. B. calyciflorus-conditionedmedium increased number of clutch, clutch size, number of offspring produced in her life,net reproductive rate and intrinsic rate of population growth of M. macrocopa, and thereverse was true for B. angularis-conditioned medium, which might suggest that the typesand activity of chemical cues released by the two rotifer species and M. macrocopa weredifferent, and depended on temperature, algal density and rotifer species. However,chemical interference interaction between B. calyciflorus or B. angularis and M.macrocopa did affect their reproduction in different degree, which partially demonstratedthe promotion of B. calyciflorus to reproduction of M. macrocopa and inhibition of B.angularis to reproduction of M. macrocopa or coexistence with M. macrocopa when thetwo rotifer species and M. macrocopa competed.4. The threshold food concentrations for population growth increased and starvationabilities of B. calyciflorus, B. angularis and M. macrocopa were determined at differenttemperatures (20℃,25℃and30℃). The results showed that threshold food concentrationfor population growth of B. calyciflorus was the highest at20℃and25℃, but the lowestat30℃. Threshold food concentration for population growth of B. angularis was thehighest at30℃. Starvation ability of B. angularis was the strongest at20℃and25℃,those of B. calyciflorus and M. macrocopa were the weakest at20℃and30℃,respectively. The results of two-way ANOVAs showed that threshold food concentrationfor population growth increased in order of M. macrocopa, B. calyciflorus and B.angularis, however, starvation ability decreased in order of B. angularis, M. macrocopaand B. calyciflorus. The differences in threshold food concentrations or starvation abilitiesof B. angularis and M. macrocopa differed with temperature, which partially explained thecompetitive outcomes between B. angularis and M. macrocopa under different conditions. |
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