Previous research on natural populations of guppies in Trinidad established that guppies are exposed to geographically varying levels and types of predation. We examined the association between three predation "treatments" and several life history parameters. There were three modes of predation or treatments: (1) Crenicichla: high predation intensity, predominantly on adult guppies; (2) Rivulus: moderate predation intensity, predominantly on juveniles; and (3) Aequidens: low predation intensity on all size classes. We found in a survey of 16 localities that guppies from the Crenicichla treatment appear to have increased reproductive investment relative to the other treatments, and they achieve this in two ways. Guppies from Crenicichla treatments devote a larger percentage of their body weight to developing offspring (Reproductive Allotment) and have shorter interbrood intervals than the other treatments. They also produce more and smaller off-spring and begin to reproduce at a smaller size than the other two treatments. Guppies from Aequidens localities tend to be intermediate between Crenicichla and Rivulus localities, or tend to resemble guppies from Rivulus localities in the various life history statistics. The results of field data from two seasons, within-stream comparisons, an introduction experiment, and a selection experiment are all qualitatively consistent with the field survey and theoretical predictions. The data therefore make a strong case for the direct role of predators in molding guppy life history patterns.