Dietary Conservatism: The Influences and Determinants of Alternative Foraging Strategies

Abstract

Dietary conservatism – the existence of alternative foraging strategies in response to novel foods – continues to be a little-known and understudied topic of animal behaviour. In every vertebrate population tested so far, some individuals are Adventurous Consumers (ACs) that rapidly accept novel foods as part of their diet, while others are Dietary Conservative (DC) and show prolonged reluctance to incorporate novel foods into their diet. However, there has been little wider recognition of the relevance of this behaviour and many questions about its mechanism and function remain a mystery. In this thesis, I aim to address this oversight to some small degree by bringing together current knowledge of dietary conservatism and exploring some of the fundamental outstanding questions about the behaviour, how it operates and what determines it. Chapter 1 is a literature review on dietary conservatism. It serves as an introduction to the topic and clarifies terminology and methodology which have become somewhat confused across different studies. I also outline crucial gaps in research on foraging strategies, some of which are the focus of the chapters that follow. In chapters 2 and 3, I explore how perception of familiarity and novelty differs among individuals with different foraging strategies. Whether or not a food (or, indeed, anything) is familiar or novel is a matter of experience, memory, and cognitive processes like association and generalization. Here is where the fundamental differences between the foraging strategies must lie. In chapter 2, I investigate whether there are degrees of familiarity; does the amount of experience with a familiar food can change animals’ preference for it, and does this relationship differ among AC and DC individuals? In chapter 3, I explore how different a food must be from the familiar to be treated as novel by individuals with different foraging strategies, and whether a difference in generalization might explain why AC and DC animals respond differently to novel foods. These chapters deal with mechanistic causes of different foraging strategies. However, they also address important concerns for experimental design, namely for how long should animals be trained on familiar foods to make them familiar, and how different must a novel food be to elicit different responses from different foraging strategies? In chapters 4 and 5 I move to explore ecological and evolutionary causes of foraging strategies and foraging strategy expression. In chapter 4, I investigate how animals’ hunger levels affect preference for familiar foods and acceptance of novel ones. Foraging strategy expression can be flexible depending on context and hunger can make animals take greater risks when foraging. It seems reasonable, then, to expect that foraging strategy expression might depend on an individual’s hunger level. One intuitive possibility is that, when hungry, animals should be more willing to accept novel foods (behave more AC) to maximize energy gain. This has never been tested and, apart from being useful to know for designing experiments, understanding how animals respond to novelty when experience different levels of hunger has substantial ecological relevance. Hunger varies seasonally and with energy demands (e.g., breeding, growing, moulting), so if foraging strategy expression depends on hunger state patterns of AC and DC behaviour might be expected at a population level as ecological circumstances dictate. Finally, chapter 5 deals with, in my opinion, the most exciting question in this thesis: what is the advantage of being DC? Explaining the existence of the DC foraging strategy and its coexistence with the AC foraging strategy in all populations is, perhaps, the most important outstanding question in dietary conservatism research. Two hypotheses to explain the benefit of being DC have been mentioned in earlier chapters – the avoidance hypothesis and the efficiency hypothesis. In this chapter I present data from the first explicit test of the latter to determine whether DC individuals are more efficient foragers than AC individuals. Such an advantage might explain not only why the DC foraging strategy evolved but why DC individuals make up a similar proportion of populations across many different studies.