Urbanization is a major form of land use change, entailing the creation of novel environments where unique dynamics and selective pressures can shape wildlife phenotypes, with behaviour being especially affected. These environmental changes can shape animal personality, resulting in differences between populations along an urbanization gradient. To fill the knowledge gap about the role of personality traits in population persistence in cities, we investigated whether the mean expression of activity, exploration and social tendency, as well as their among-individual variance and within-individual variance, changed between urban, suburban and rural populations. We conducted 490 repeated arena tests on 169 Eurasian red squirrels, Sciurus vulgaris , to estimate personality trait expression through an open field test followed by a mirror image stimulation test. We found no differences in the mean expression of activity, exploration and social tendency between populations living at different degrees of urbanization, even if exploration decreased at higher population densities. However, we observed minor changes in the variance components of all the personality traits. Rural populations tended to be more heterogeneous (higher among-individual variance) in the expression of exploration and social tendency, and individuals in suburban populations were more flexible (greater within-individual variance) in activity than rural conspecifics. Our findings provide insights into how the variance components change along an urbanization gradient, a topic still largely unexplored despite its implications for ecology, evolution and management of populations, as it could support population response to the highly dynamic urban environments.
Tranquillo et al. (2026) studied this question.