The Effects of Elevated Population Density on North American Red Squirrel (Tamiasciurus hudsonicus) Behavior

Abstract

Urbanization is one of the most significant drivers of changes in wildlife population densities, as it often results in habitat fragmentation, degradation, and loss, decreasing the suitability of habitat for wildlife. Many species in urban areas experience higher population densities compared to undisturbed areas. My study is predicated on an experiment that elevated the population density of wild North American red squirrels (Tamiasciurus hudsonicus). The purpose of this study was to investigate the behavioral changes as a result of this increase in population density and whether any resulting behavioral changes are a result of natural selection, as opposed to behavioral plasticity. I leveraged a long-term behavioral database from the Kluane Red Squirrel Project to assess the differences in two behaviors (activity and aggression) recorded from squirrels in a standardized behavioral assay (open-field trial and mirror-image simulation) between the high-density experimental area and lower-density control areas. I then performed behavioral tests on individuals from the high-density area to assess how the number of maternal generations an individual’s lineage had experienced in the high-density area affected activity level, aggression, and docility. Previous studies show that female red squirrels that were more aggressive and less active in conditions where competition was elevated had higher reproductive success. Because of this, I predicted a decrease in activity level and increase in aggression with elevated population density. Because these behaviors have been shown to be genetically heritable in red squirrels, I predicted this would be a result of natural selection and there would be an increase in the frequency of these behaviors with increasing maternal generation time in the area of elevated density. My results showed squirrels from the area with elevated population density were significantly less active than those from the control areas. There was no relationship with aggression between density levels, or with any behavior and maternal generation time. These results show that elevated population density could influence behavior but suggests that perhaps these changes are due to behavioral plasticity rather than natural selection.