Lecture F2 (2024-10-29): The Role of Time in Foraging and Predation

In this lecture, we focus on adaptations to foraging that are shaped by opportunity cost and risk of starvation. Before getting to that, we open with a short discussion of different trophic strategies and the time pressures on each of them. After discussing the ways in which sit-and-wait/ambush predators can use lures and special placement to alter the rate at which they encounter prey, we then switch our focus to mobile predators that make decisions about how long to stay in patches of prey items that they encounter in a heterogeneous, clumpy environment (i.e., how to balance instantaneous rewards of local exploitation with the costs of lost opportunity from continuing to search more broadly). This discussion lets us introduce the Marginal Value Theorem (MVT) of optimal foraging theory and interpret it as a biological version of the equimarginal principles used in economic analysis of consumer behavior. We then shift to thinking not about opportunity cost so much as the risk of starvation for foragers that must reach a minimum threshold for energetic gain by a certain time in order to survive. This lets us introduce risk-sensitive foragers (including risk-prone and risk-averse foragers), the notion of a "stretch goal," and the notion of "bet hedging."

Topic highlights:

• Holling's disc equation
• handling time and its role in the predator saturation/swamping/starvation reproductive strategy of potential prey
• trophic strategies and how they relate
• sit-and-wait/ambush predation and luring
• central-place foragers
• the "patch model" from optimal foraging theory and the problem of choosing the best patch residence time
• diminishing marginal returns and opportunity cost
• marginal value theorem (MVT) and the equimarginal principle
• other applications of the MVT, including:
  • optimal diving models
  • parasitoid oviposition
  • electric vehicle charging (speculative)
• risk-sensitive foraging
  • stretch goals and bet hedging

Important terms: predator saturation/swamping/starvation, trophic strategies, carnivory, hematophagy, herbivory, frugivory, folivory, omnivory, scavenging, carrion, predation, sit-and-wait/ambush predators, pursuit predation, parasitism, parasitoid, parasitoid oviposition, micro-predator, kleptoparasitism, active hunter/predator, foraging, central-place forager, handling time, opportunity cost, optimal foraging theory (OFT), patch, marginal returns, patch residence time, marginal value theorem (MVT), equimarginal principle, optimal diving models, risk-sensitive foraging, risk prone/risk averse, stretch goal, bet hedging