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Abstract:
Three natural Daphnia populations in which the previously established impact of invertebrate predators on the death rate (but not on the birth rate) were investigated. Two other cladoceran populations primarily affected by food were used for comparison. The effect of predators on the per capita birth rate of Daphnia was detected by decomposing changes in birth rate into components dependent on changes in egg development rate, mean clutch size, and proportion of adults and then comparing them. This method revealed short-term changes in the proportion of adults, which dominated changes in birth rate. The effect can be attributed to size-selective feeding of the invertebrate planktivores that normally prey on young daphnids, and it did not occur in food-dependent cladocerans. Invertebrate predation pressure tends to increase the per capita birth rate of Daphnia, which may provide a mechanism that stabilizes prey