Personality differences between native and invasive populations of the eastern gray squirrel

Invasive alien species are a major threat to global biodiversity, thus recent work has aimed to identify traits of successful invaders to better inform management efforts and predictions of future invasions. Personality and intraspecific behavioral variation are important characteristics that may mediate individuals’ and species’ invasion success. However, to the best of our knowledge, no study to date has looked at the personality differences between an invasive species in its native and invasive ranges. Here, we filled this gap by studying the sociality and self-grooming behavior of eastern gray squirrels (Sciurus carolinensis) in their native range in Northeastern USA and in their invasive range in Italy. We used the open field and mirror-image stimulation tests to assess the personality of 466 unique gray squirrels, including 271 individuals from the native population and 195 from the invasive population. We found that both the distribution and the median value of sociality significantly differed between populations, with a higher median value of sociality among invasive squirrels, while the distribution and median of self-grooming, a proxy for stress-coping ability, did not significantly differ between populations. Overall, we demonstrate that certain personality traits differ between native and invasive populations, highlighting the importance of considering intraspecific behavioral diversity for the prediction and management of invasive alien species. We urge further work to elucidate the mechanisms behind such personality differences.