Safe Periods and Safe Activities: Two Phenological Responses to Mortality

Phenology is often thought to evolve mainly in response to food availability, yet recent studies have focused on predation. Predation may explain apparent mismatches between phenology and resources. One type of phenological response to predation involves shifting phenology from a period of high to low predation (i.e., a safe-period strategy). This strategy presupposes variation in predation over time due to environmental factors such as the number or diversity of predators. Predation varies not only over time but also among different activities like reproduction and dormancy. Alternative activities involve alternative behavioral or physiological states, and different locations where they take place influencing predation risk. Phenological responses to predation may involve shifting from a high risk activity to a safer one, resulting in increased survival (i.e., a «safe-activity» strategy). This strategy may theoretically evolve under environmental conditions associated with constant predation over time, but assumes variation in predation among activities. Safe-period and safe-activity strategies are not mutually exclusive, but assume different conditions for their evolution. On the basis of a literature review, our goal was to: (1) propose a classification of phenological responses to predation according to their evolutionary context, including mean population responses and interindividual differences (degree of synchrony); (2) to show how these two strategies may explain the lack of support for the idea that phenology responds primarily to food availability; and (3) to propose several approaches for testing the influence of predation on phenology. Our review highlights the relevance of studying phenology on multiple scales, thereby integrating several interspecific interactions (communities scales) and multiple activities (annual scale), and studying synchronicity and the pace-of-life (inter-individual scale).