Behavioural and trophic variation within a well-established invasive round goby population

An animal's behavioural traits can influence the outcomes of ecological interactions within their food web, including what they eat, their vulnerability to predation and who they compete with. Despite this, few studies have directly measured links between among-individual behavioural and trophic variation. Invasive species like the round goby, Neogobius melanostomus, are often found to have consistent among-individual differences in behaviour within and between populations across their invasion front. Therefore, an individualized approach to invasive populations and their ecological interactions may be valuable to understanding their impacts on recipient ecosystems. Using nonlethal methods to measure trophic variation (i.e. stable isotope analysis via fin clips) and passive individual tagging, we analysed behavioural trait/personality variation and trophic variation to explore links between the two. Focusing on an established population of round gobies in the Guldborgsund strait in the southwest Baltic Sea, we found significant among-individual variation in bold–exploratory traits in novel environment and refuge emergence assays. We also found strong intraspecific trophic variation, with particularly high variation in carbon-12 – carbon-13 (δ¹³C), suggesting that individual round gobies differ in what they are feeding on and/or where they forage. Diet reconstruction results support previous studies showing that gastropods and bivalves are major contributors to their diet, but the large differences in isotope values suggest that individual variation influences how they interact with prey communities. There were few links between behavioural and trophic variation; nevertheless, this study shows that measuring behavioural–trophic links is a viable approach for exploring whether and how behavioural traits may influence individual level ecological variation.