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Abstract

Cladocerans, like many other invertebrates, continue to grow after beginning to reproduce, and their reproductive capability increases with size. What are the demographic consequences of this strategy of indeterminate growth? Here we present results of laboratory experiments in which we measured reproductive strategies of two large, similar cladoceran species, Daphnia pulex and D. pulicaria under high and moderately limiting food conditions. From the experimental data, we calculated the intrinsic rates of increase r for each reproductive strategy. We also estimated the effect on r of changing the pattern of allocation of biomass to reproduction. The results suggest that the daphnid strategy may represent an evolutionary compromise between strategies that maximize r and strategies that maximize total reproductive output.