Prey have been shown to adjust a large range of phenotypic traits in response to changes in predation risk, from morphology to life history. Specifically, individuals are predicted to decrease in investment in current broods when faced with increased predation risk (for adults). Additionally, since prey populations are comprised of individuals that differ in susceptibility to predation risk, we predicted that birds with phenotypes that are associated with increased predation risk (such as more active individuals) would respond more strongly. This study was designed to determine if predation risk affected how individuals invest in current reproduction by examining individual variance and covariance components of prey behavioral and life history traits in the field in two years of experimental manipulation of predation danger using playback in 12 populations of wild birds. Half of the populations received the same treatment both years, allowing us to assess treatment specific repeatabilities, and half alternated treatments in order to assess cross context correlations and crossing of reaction norm slopes. To comprehensively evaluate the effects of predator risk we used path analysis to compare the overall relationship between behavior and life history across treatments.
We found that the relationship between exploration behavior and life history changed with treatment. Specifically, fast explorers (more susceptible individuals) bred earlier in response to increased perceived predation while slow explorers (less susceptible individuals) delayed breeding. Behavioral types differed in life-history decisions when faced with perceived predation risk, implying that predation risk can potentially affect evolutionary processes over and above the selection pressures induced by predation and highlighting the importance of incorporating individual differences into the study of perceived predation risk and its consequences for micro-evolution in natural populations.