食物质量和种间竞争对盔型溞(Daphnia galeata)和脆弱象鼻溞(Bosmina fatalis)种群增长的影响

Effect of food quality(C ∶ P ratio) and interspecific competition on population growth of Daphnia galeata and Bosmina fatalis

竞争是调控水体浮游动物群落结构的生物因素之一.根据"大小效率假说",大型滤食性枝角类对小型枝角类有竞争优势.然而,大型滤食性枝角类体内磷含量通常高于小型枝角类,生长比小型枝角类更容易受食物磷缺乏的影响,食物的磷缺乏可能会改变大型枝角类和小型枝角类之间的竞争结果.本研究比较分析了食物碳磷比对两种常见枝角类(盔型溞(Daphnia galeata)和脆弱象鼻溞(Bosmina fatalis))的种群增长率、种群密度及种间竞争关系的影响.实验设计了3个食物质量处理组:高磷(碳∶磷=105)、中磷(碳∶磷=740)和低磷(碳∶磷=2400),食物浓度均为2 mg C/L蛋白核小球藻(Chlorella pyrenoidosa);针对每一个食物质量处理组,盔型溞和脆弱象鼻溞分别单独培养或混合培养.盔型溞和脆弱象鼻溞平均最大种群密度分别为378～893和364～2399 ind./L;平均种群增长率分别为0.11～0.14和0.09～0.16 d-1;平均体长分别为1.53～2.50和0.25～0.35 mm.种群增长率和体长均随着食物碳磷比的升高而显著下降,而最大种群密度在中磷处理组显著高于其它两个处理组.盔型溞种群增长率在单独培养和混合培养间无显著差异;脆弱象鼻溞种群增长率在混合培养时显著低于单独培养时.在高磷和中磷处理组,盔型溞最大种群密度在单独培养和混合培养间无显著差异,在低磷处理组,混合培养时最大种群密度显著低于单独培养时;在高磷处理组,脆弱象鼻溞最大种群密度在单独培养和混合培养间无显著差异,在中磷和低磷处理组,混合培养时显著低于单独培养时.结果表明,在食物碳不缺条件下,不管食物磷是否缺乏,盔型溞均比脆弱象鼻溞有竞争优势.

Competition for food resource is one of the crucial biological interactions in nature.According to the size-efficiency hypothesis,large filter-feeding cladocerans are viewed to be superior to small cladocerans.However,large filter-feeding cladocerans generally tend to have higher phosphorus content than small cladocerans,and food stoichiometry quality may affect the outcome of competition among them.We examined the effects of food stoichiometry quality(different carbon phosphorus ratios(C∶P))and interspecific competition on the population growth of two common cladocerans species in South China,Daphnia galeata and Bosmina fatalis.D.galeata and B.fatalis were fed saturating concentrations of food(Chlorella pyrenoidosa,2 mg C/L)of high P(C∶P=105),medium P(C∶P=740),and low P(C∶P=2400),and grew alone or together.Peak population densities varied from 378 to 893 ind./L and 364 to 2399 ind./L,and population increase rates varied from 0.11 to 0.14 d^-1 and 0.09 to 0.16 d^-1 for D.galeata and B.fatalis,respectively.Mean body length varied from 1.53 to 2.50 mm for D.galeata,and 0.25 to 0.35 mm for B.fatalis.Rate of population increase and mean body length in both species decreased with the increasing of food C∶P ratio,regardless of growing alone or together.However,peak population densities in both species were much higher under medium P condition than those under high and low P conditions,regardless of growing alone or together.In mixed cladoceran cultures,population increase rates of D.galeata were not significantly different from those cultured alone,while increase rates of B.fatalis were much lower than when cultured alone,regardless of the C∶P ratio in food.Only under low P condition did the peak densities of D.galeata tended to be much lower in mixed cladoceran cultures than when cultured alone.For B.fatalis,peak population densities were much lower in mixed cultures than when cultured alone in medium and low P conditions.Our results suggest that D.galeata is competitively superior to B.fatalis irrespectively of food C∶P ratio when food concentration is high enough for their population growth.