The Effects of Individual and Environmental Variation on a Food Hoarding Rodent’s Stored Resources
Many animals collect food during the present to store for later, a behaviour that is known as ‘hoarding’. Food hoarding allows animals to ensure their own future resource availability, rather than relying on resources in the environment, especially if the cost of foraging is prone to fluctuation. This behaviour has evolved repeatedly in animals, and it is widely accepted that this is because food hoarding conveys a fitness benefit. Yet despite this ecological and evolutionary advantage, the mechanisms and circumstances that influence food hoarding behaviour are still poorly understood. In this thesis, I use a multi-phase experiment with captive Syrian hamsters (Mesocricetus auratus) to integrate information about resource fluctuations, individual behavioural variation, and internal energy balance to understand how food hoarding is connected to both an individual’s internal and external environment. In Chapter 2, I show that hamsters do not hoard additional food when faced with alternating days of good and bad foraging conditions, as predicted for fat storing animals in fluctuating environments by Optimal Foraging Theory’s ‘Insurance Principle’. In Chapter 3, I establish that hamsters store the majority of energy exogenously in their hoard rather than endogenously as fat. I also show that this behaviour is repeatable, that is, variable among individual hamsters but consistent within the same hamster over time. In Chapter 4, I demonstrate that despite minimal endogenous fat storage, as shown in the previous chapter, the hormone leptin, a primary endocrine regulator of energy balance, is related to fat and energy consumption rather than food hoards directly. Taken together, the results of my thesis contribute to our understanding of the environmental circumstances and internal mechanisms that influence food hoarding in Syrian hamsters. In this thesis I demonstrate that while food hoarding as a behaviour is highly variable among individuals, and consistent within individuals, the accumulated hoard itself does not appear to be physiologically maintained analogously to endogenous fat stores or responsive in the same ways to environmental fluctuation. Understanding how animals combine their physiology and behaviour to effectively meet energetic demand during environmental fluctuation is critical, especially as the Anthropocene environment becomes increasingly unpredictable.