Francis Quang-Hai Dinh’s initial summer at McGill University was spent traversing Montreal-area parks on his bicycle in search of squirrels. He visited nearly 200 green spaces across the region, from Mirabel to Saint-Bruno, meticulously observing and documenting over 800 grey and black squirrels. What began as an undergraduate assignment evolved into a personal project driven by his fascination with how the city’s layout and meandering waterways influence evolution subtly.
Expressing his growing affection for squirrels, Dinh shared, “I developed a fondness for them after spending considerable time observing and contemplating them. Squirrels are often overlooked as mere pests, but they are indeed a form of wildlife.” Due to the unavailability of a car and limited public transportation options in suburban areas, Dinh heavily relied on his bicycle to explore as far as possible, making him the sole researcher known to conduct manual squirrel surveys park by park throughout the region.
Research revealed that, on average, approximately 12% of squirrels in Montreal exhibit black coloration. Notably, as Dinh ventured further north, the prevalence of black squirrels increased. In regions just north of Laval, he discovered that up to 40% of squirrels had black coats, a descriptor for darker squirrel fur differing from the typical grey hue. On Laval Island, around 20% were black, while on Montreal Island, the figure stood at approximately 15%. Moving to the south shore of Montreal, the percentage dropped significantly to only two to three percent.
The study delineated three primary factors contributing to this phenomenon, with temperature ranking as the most significant. As temperatures decrease further north, the prevalence of black squirrels rises due to their ability to absorb heat more effectively than grey squirrels. Additionally, forest cover plays a crucial role, as denser tree canopies create a darker environment where black squirrels blend in better.
The study’s lead author, Allison Roth, an assistant professor at the University of Missouri and former McGill postdoctoral fellow, emphasized that the research focuses not solely on squirrels but employs them as a model to examine how urban landscapes influence evolutionary changes. Urban environments, characterized by diverse neighborhoods, varying tree cover levels, and distinctive boundaries like Montreal’s waterways, create nuanced environmental variations that can prompt genetic and physical adaptations within the same animal population.
Roth highlighted Montreal’s unique geographical features, particularly its segmentation by the St. Lawrence River and tributaries, which create isolated pockets resembling distinct islands. This spatial configuration potentially influences patterns of squirrel melanism, underscoring the importance of understanding evolutionary processes in such environments.
Contrary to previous studies comparing urban and rural animal evolution broadly, this research delves into wildlife changes on a neighborhood-specific basis. By considering fine-scale variations in vegetation structure and microclimates, the study challenges the notion that human development alone drives evolutionary shifts. Urban sprawl, altered local temperatures, reduced tree cover, and natural barriers like riverways collectively contribute to shaping wildlife adaptations.
The study, titled “Fine-scale spatial variation in eastern grey squirrel melanism across a complex urban landscape,” offers valuable insights into how environmental factors influence evolutionary patterns. It emphasizes the indirect impact of urbanization on melanism, mediated by local environmental variables. The findings are part of a special feature by five ecology journals focusing on collaborative efforts to address significant ecological inquiries.
Reflecting on his experiences, Dinh acknowledged a shift in his perspective on wildlife, remarking, “The dichotomy between city life and nature is a common notion. However, wildlife persists despite our modifications, reminding us of their resilience.”