© 1996 by The Society for Integrative and Comparative Biology
Risk-Sensitive Foraging, Fitness, and Life Histories: Where Does Reproduction Fit into the Big Picture?1
Institute of Applied Mathematics & Centre for Biodiversity Research, University of British Columbia Vancouver, BC V6T 1Z2, Canada
Risk-sensitive foraging may occur whenever feeding success has non-linear effects on fitness. Models of sensitivity to variation in amount of food obtained have concentrated on foraging in order to survive even though feeding during growth, migration, or reproduction can have strong and non-linear effects on fitness. I illustrate how risk-sensitive foraging for reproduction could differ from risk-sensitive foraging for survival using two simple models. Each model assumes that organisms must accumulate some threshold amount of resources before they can reproduce. In the first model, additional resources above the threshold lead to increased reproductive success. Here variance in feeding success can be advantageous even when the mean gain would allow organisms to reproduce. In the second model, early breeding is superior to late breeding because recruitment rate declines over time. Here a symmetrical distribution in foraging rates results in a skewed distribution of breeding times. Despite this, variance in feeding success may be advantageous even when the seasonal decline in recruitment is linear. The advantage of risk is much larger if foragers can switch freely between feeding options. These two models are united by "the bankruptcy effect" because all failures to reproduce carry the same consequences. These simple models suggest that risk-prone foraging may be likely when factors other than survival are important for fitness. Finally, I advocate using a mix of modelling techniques, note the implicitly risk-sensitive nature of stochastic dynamic programming, and speculate on potential connections between risk-sensitive foraging and theories of life histories in variable environments. INTRODUCTION visit restaurants that provided twice