Links between personality and individual niche in the freshwater fish Gobiomorphus cotidianus

All individuals within a population are unique. Individual variation in behaviour – or animal personality – occurs consistently throughout the animal kingdom. Understanding how individuals vary in their behaviour is imperative in fully deducing the impact that animal personalities can have at the population or even ecosystem level. Resource use has also been shown to consistently differ between individuals in a population, and can have effects on the strength and variety of interactions an animal has within its ecosystem. At present, there has been very little research on how the personality of an animal affects individual resource use, especially the comparison between behavioural variation and diet in a natural setting. The aim of this research was to investigate individual behavioural variation and resource use in a New Zealand freshwater fish (common bully, Gobiomorphus cotidianus), and understand how these individual parameters may affect both each other and an individual fish’s fitness. The individual behavioural variation of common bullies was examined through repeated assays of boldness, aggression and exploration in 93 fish. The habitat use, diet and growth of individuals were also repeatedly measured in pond mesocosms that mimicked the bullies’ natural ecosystem. Behavioural types, in particular individual boldness, were found to be moderately to strongly repeatable through time. There were also significant correlations between all behavioural types, where bolder fish were consistently more aggressive and more exploratory, establishing the existence of a proactive/reactive behavioural syndrome. 50% of the total dietary niche width of the population was accounted for by individual specialisation, while habitat use was found to be only weakly repeatable. It was found that behaviour was correlated with individual resource use in fish that had their personality analysed prior to their resource use, where more exploratory, less bold fish ate larger prey in shallower habitats. In contrast, correlations in fish that had their behaviour assayed after placement in mesocosms were non-significant. There were also no significant correlations between an individual’s growth, and its behaviour or resource use, though there was a near-significant tendency for more proactive fish to have slower growth rates. Overall, the discovery of this behavioural syndrome and resource specialisation is important as it highlights the uniqueness in how each individual reacts to different situations and how these could then feed through to alter predator-prey interactions. This could then affect abundances of species at trophic levels with which they are connected, and potentially the functioning and services an ecosystem provides. Ultimately, this study advances our understanding of the individualities of the behaviour and niche within this species, and gives insight into the possible mechanisms for effects that animal personalities can have on ecosystems