Predation pressure has often been postulated as a major selective force for the evolution of life histories, with high predation (particularly on small sizes) resulting in a fast-living strategy characterized by fast growth, early maturation, and short lifespan. However, due to the difficulty of assessing actual predation pressure in the wild, evidence for a role of predation in life-history evolution is rare. We examined the relationship between avian predation and life-history strategy in replicate populations of fast and slow-living garter snake ecotypes. To assess avian predation, we first compiled a list of known and suspected predators based on direct observations of predation events recorded in our long term detailed field notes from 1978 – present. Furthermore, we added to this list with published records of snake predation involving avian species known to occur in our study site, and a novel method of inferring predator identity via analysis of bill marks on live snakes. Using this list of candidate predators, we conducted surveys quantifying predator incidence in replicate habitats of both ecotypes. We found that known and suspected predators are more abundant in habitats of the fast-living ecotype than in those of the slow-living ecotype. We also show a higher incidence of bill marks on slow-living snakes, which may indicate an increased effectiveness at escaping predation attempts. In general, we provide evidence to suggest that predation pressure may indeed have been an important selective force in the evolution of fast growth and early maturation in the fast-living ecotype and may continue to constitute an important source of extrinsic mortality leading to differences in lifespan between the two ecotypes.
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Vol. 170 • No. 1