The ecological impacts of the indirect effects of predators are well established, but the evolutionary consequences are unknown. Predators often decrease prey density, which indirectly increases the resources available to surviving prey. This ecological effect could provide a link to evolution because it is generally assumed that resource availability influences life history evolution. Yet, predictions from theory that consider food availability are inconsistent, and evidence for an important role of resources in shaping life history evolution is absent. We compared life history traits in a Trinidadian killifish, Rivulus hartii, from fish communities that differ in predation intensity; predators are associated with lower population density and faster growth rates. To determine whether the indirect effects of predators influence evolutionary change, we reared second-generation-born fish under two food levels that approximated natural differences in resources between communities. Rivulus from sites with predators are younger and smaller at maturity. They have increased reproductive investment and produce many small eggs and smaller hatchlings. Such divergence is predicted as a direct effect of predation. We also found significant interactions between predator community and food level for age and size at maturity, fecundity, and egg size. These interactions, whereby the differences between communities were more pronounced at high-food levels, argue that evolution in Rivulus has been influenced by the indirect effects of predators mediated through resource availability. Rivulus from sites with predators better exploit the higher resources in those habitats. Therefore, both direct and indirect effects of predators have evolutionary consequences.density ͉ guppy ͉ resource availability ͉ trophic cascade R esource availability has historically been considered an important selective pressure on the evolution of life histories. For instance, Lack (1, 2) proposed that clutch size variation is driven by food limitation, although differences in resource availability were implicitly assumed in r-and K-selection (3, 4). Despite this interest, evidence demonstrating how resource availability molds the evolution of general life history strategies is severely lacking. One reason is that life history theory has failed to yield consistent predictions as to how evolution should proceed when resources are limited (5-7). Furthermore, differences in resource availability often covary with additional ecological selective pressures such as population density and predators. For example, although predators have the direct effect of increasing mortality rates, they also have the indirect effect of reducing the population density of prey and possibly increasing resource availability to surviving prey (8-10). Therefore, the indirect effects of predators, which are a prevalent feature of ecological systems (8), potentially have evolutionary consequences that are mediated through resource availability. However, theory suggests that evolutionary...