On the Origin of Risk Sensitivity: the Energy Budget Rule Revisited

TL;DR

This paper revisits the energy budget rule in risk-sensitive foraging theory, proposing a gradual version that better explains empirical data and accounts for varying selection pressures near survival thresholds.

Contribution

It introduces a 'gradual' budget rule derived from the continuous nature of risk sensitivity, extending and refining the traditional all-or-nothing budget rule.

Findings

The gradual budget rule aligns with empirical findings challenging the conventional rule.

It shows the conventional rule applies mainly when expected reserves are near survival thresholds.

The new rule accounts for situations with low selection pressure where the traditional rule fails.

Abstract

The risk-sensitive foraging theory formulated in terms of the (daily) energy budget rule has been influential in behavioural ecology as well as other disciplines. Predicting risk-aversion on positive budgets and risk-proneness on negative budgets, however, the budget rule has recently been challenged both empirically and theoretically. In this paper, we critically review these challenges as well as the original derivation of the budget rule and propose a `gradual' budget rule, which is normatively derived from a gradual nature of risk sensitivity and encompasses the conventional budget rule as a special case. The gradual budget rule shows that the conventional budget rule holds when the expected reserve is close enough to a threshold for overnight survival, selection pressure being significant. The gradual view also reveals that the conventional budget rule does not need to hold when the expected reserve is not close enough to the threshold, selection pressure being insignificant. The proposed gradual budget rule better fits the empirical findings including those that used to challenge the conventional budget rule.