Partial clutch predation, dilution of predation risk, and the evolution of intraspecific nest parasitism

Distributing eggs among multiple nests may have a selective advantage over laying eggs in one nest when stochastic events, Such as predation, affect individuals of the same phenotype differently. However, an earlier analysis revealed that the mean fit, all eggs in one nest when predation destroys entire clutches. However, it preness of such an egg-spreading strategy is equal to putting dation typically results in partial clutch loss, distributing eggs among multiple nests may provide a selective advantage. We investigated the possibility that partial clutch loss could favor egg-spreading strategies by modeling mean fitness Under a variety of egg-distributing strategies with partial nest predation. We found that higher fitness resulted from distributing eggs among multiple nests that contained at least as many eggs as a single nest containing the eggs of one female. The highest fitness resulted when eggs were in large clutches, because of predator-dilution effects. The fitness differences among egg-distribution strategies increased as predation rates, frequency of partial clutch loss, and the number of eggs destroyed in each partial predation event increased. We also examined the invasibility of pure and mixed parasitic and nesting strategies. Nest parasites may increase their fitness by spreading eggs among multiple nests that contain more eggs than would be present if the), were nesting alone, but only a pure parasitic strategy call invade a population Of non parasites when the number of eggs; laid is constrained.