Incorporating Predation Risk into the Marginal Value Theorem: The Risk-MVT and Optimal Boldness

Core Concepts

Individuals should generally be bolder in riskier habitats, as the risk-MVT predicts that optimal risk exposure increases with the level of predation risk.

Abstract

The article introduces the concept of the risk-MVT (rMVT), which generalizes the classic Marginal Value Theorem (MVT) to incorporate the effects of predation risk on optimal foraging strategies. The rMVT retains the structure and graphical simplicity of the original MVT, but shifts the optimization domain from regular time to expected dose of risk (micromorts).
The authors classify different types of predation risk scenarios, ranging from disturbance (non-lethal interruptions) to escape (forced patch leaving) to lethal predation. They show how each risk scenario can be incorporated into the rMVT framework, and how the rMVT relates to and generalizes Brown's Giving-Up Density (GUD) theory.
Key insights from the rMVT include:

Greater risk in patches can either decrease or increase optimal residence times and giving-up densities, depending on the specific risk scenario.
Experimental observations with predation risk suppressed can differ from field observations, as the rMVT predicts a negative correlation between the two in some cases.
The rMVT introduces a metric of "optimal boldness" - the amount of risk an individual is willing to take per patch visit. This boldness generally increases with the level of risk in the habitat, suggesting individuals should be bolder in riskier environments.
The rMVT provides a unified framework to understand the effects of diverse predation risks on optimal foraging strategies, reconciling the "resource acquisition" perspective of the MVT and the "fear" perspective of GUD theory.

Stats

"As of May 2023, Charnov's 1976 article had been cited 3,485 times and Brown's 1988 article 1,031 times, according to the Scopus citation database."
"The relative overlap of their citing articles or citing authors, as quantified by Sorensen index, never exceeded a low 15% and are on a downward tendency."

Quotes

"Charnov's 1976 publication is now regarded as iconic by its publishing journal (Rosenberg 2020)."
"Both articles continue to be abundantly cited, at remarkably similar paces, their relative rate of citations quite stable over the past 20 years (Fig. 1a)."

Key Insights Distilled From

Taking fear back into the Marginal Value Theorem: the risk-MVT and optimal boldness

by Calcagno,V.,... at www.biorxiv.org 11-02-2023

https://www.biorxiv.org/content/10.1101/2023.10.31.564970v3

Deeper Inquiries

How might the predictions of the risk-MVT change if foragers have the ability to actively assess and respond to predation risk levels when selecting patches

If foragers have the ability to actively assess and respond to predation risk levels when selecting patches, the predictions of the risk-MVT may change in several ways. Firstly, foragers may exhibit more nuanced behaviors in response to varying levels of risk. They could adjust their patch-leaving decisions based on real-time assessments of predation risk, leading to more dynamic foraging strategies. This could result in non-linear relationships between risk levels and optimal residence times, as foragers may exhibit different responses depending on the perceived level of risk at a given time. Additionally, foragers may show adaptive responses such as increased vigilance or avoidance behaviors in patches with higher risk levels, which could impact their foraging efficiency and resource acquisition rates. The risk-MVT framework would need to incorporate these dynamic adjustments and behavioral responses to accurately predict foraging strategies in environments where foragers actively assess and respond to predation risk levels.

What are the potential evolutionary implications of the risk-MVT's prediction that individuals should generally be bolder in riskier habitats

The risk-MVT's prediction that individuals should generally be bolder in riskier habitats has significant evolutionary implications. In riskier habitats, individuals that exhibit bolder behaviors, such as staying longer in patches despite the presence of predators, may have a competitive advantage in terms of resource acquisition and fitness. By being more persistent in risky environments, these individuals may be able to exploit high-quality patches more effectively, leading to increased energy intake and potentially higher reproductive success. Over time, natural selection may favor individuals with bolder foraging strategies in riskier habitats, as they are more likely to survive and reproduce in challenging environments. This could drive the evolution of boldness as an adaptive trait in response to predation risk, shaping the foraging behaviors of individuals within a population.

How could the risk-MVT framework be extended to incorporate the effects of social interactions, such as competition or cooperation, on optimal foraging under predation risk

To extend the risk-MVT framework to incorporate the effects of social interactions on optimal foraging under predation risk, one could consider the influence of competition and cooperation among individuals in a group or population. Competition for resources could impact optimal foraging strategies, as individuals may need to balance the benefits of staying in a patch longer to maximize gains with the risks associated with increased exposure to predators. The risk-MVT could be modified to include parameters that account for the presence of competitors and the potential trade-offs between resource acquisition and predation risk avoidance in competitive environments. Additionally, the framework could be expanded to explore how cooperative behaviors, such as group foraging or alarm calling, influence optimal foraging decisions in the presence of predators. By integrating social interactions into the risk-MVT, researchers could gain insights into the complex dynamics of foraging behavior in social species and the evolutionary implications of cooperative and competitive strategies in the context of predation risk.