Life-history evolution in guppies (Poecilia reticulata) 6. Differential mortality as a mechanism for natural selection.
The authors have previously reported a correlation between the life-history patterns of guppies and the types of predators with which they coexist: guppies in localities with a high incidence of predators (HPL) matured at an earlier age and devoted more resources to reproduction than those in low predator localities (LPL). It was hypothesized that natural selection acted in a manner such that guppies experienced high adult mortality in HPL and high juvenile mortality in LPL (age-specific mortality hypothesis). To test this hypothesis, mark-recapture experiments were conducted on guppies of different sizes in streams in which different types of predators predominated. It was found that guppies in HPL had significantly higher mortality rates than those in LPL, but these higher mortality rates were uniformly distributed across all size classes. The results contradict the prediction of the age-specific mortality hypothesis.