Impact of urbanization and anthropogenic food sources on the ecology and energy budgeting of the Eurasian red squirrel (Sciurus vulgaris)
Final Report Abstract
Human activities are constantly changing the earth in multiple ways. Urbanization is amongst the major modifications and challenges wildlife with multiple stressors, such as habitat fragmentation, largely built-up area, changed vegetation, frequent encounters with humans, traffic, noise or pollutants. Many species cannot tolerate these extensive disturbances. Consequently, urbanization contributes to the globally ongoing biodiversity loss. Nonetheless, some species seem to be successful in cities and even occur in higher densities than in their natural habitats. This phenomenon is likely a result from fewer natural predators and buffered environmental conditions in terms of higher ambient temperature (i.e. the "urban heat island") and year-round access to human refuse and supplemental feeding. However, urban species might suffer from side-effects on a long-term basis. In the scope of this project, we investigated the response of a common mammal to urbanization and associated changes in food availability and ambient temperature. Eurasian red squirrels (Sciurus vulgaris) are naturally forest dependent and favor seeds and nuts in their diet, but forage on a great variety of foods, depending on availability. We combined a field study in urban parks in the core of a large city and in a nearby forest, with experiments in outdoor enclosures to study the ecology, foraging behavior and physiology of urban versus forest squirrels. Despite higher population densities in all urban study sites compared to the forest, we identified substantial differences between the parks, likely related to pronounced differences in natural and supplemental food abundance. This highlights the heterogeneity of urban habitat patches where environmental conditions can change within few 100 meters. In subsequent experiments, urban squirrels differed from forest squirrels in their food choice when they were free to choose, mainly by eating higher amounts of non-natural food items and presumably health-relevant amounts of sugar. Body mass and condition, both relevant for survival and reproduction in squirrels, were lower though, which raises concerns about an adequate nutrient supply. Besides this, energy expenditure, a measure that directly relates to body heat production in mammals, was less responsive to a decrease in ambient temperature in urban squirrels. This is likely related to the warmer urban temperatures and more stable food supply. However, our results also pointed towards energy savings of the urban squirrels when it is cold, but higher expenses at warmer temperatures. The latter is worrying with regard to the global climate change and associated temperature rise, particularly in cities. The results of our project underline that high densities might not necessarily imply thriving populations on a long-term basis. Studying whether and how urban and rural populations differ is crucial for a better understanding of urban biodiversity and for mitigating negative side effects. Restricting the access to human refuse and guiding the public about adequate feeding might be important tools for urban planning and conservation to ensure a healthy diet for urban wildlife. Besides this, urban greening measures that entail cooling effects can be crucial, not only to create habitat, shelter and appropriate food for wildlife, but also to mitigate the effects of climate change in cities for both, humans and wildlife.
Publications
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Crowded in the city: Effects of urbanization and anthropogenically-provided food sources on the ecology and energy budgeting of the Eurasian red squirrel (Sciurus vulgaris). International Squirrel Colloquium, Galway, Ireland, 2019.
Wist B.; Probst B.; Reher S.; Teich E.; Thomas L.; Turner J. & Dausmann KH
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Sugar addicted in the city: impact of urbanisation on food choice and diet composition of the Eurasian red squirrel (Sciurus vulgaris). Journal of Urban Ecology, 8(1).
Wist, Bianca; Stolter, Caroline & Dausmann, Kathrin H.
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City comfort: weaker metabolic response to changes in ambient temperature in urban red squirrels. Scientific Reports, 13(1).
Wist, Bianca; Montero, B. Karina & Dausmann, Kathrin H.
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Food availability and population parameters for squirrels differ even in neighbouring urban parks. Urban Ecosystems, 27(2), 531-544.
Wist, Bianca & Dausmann, Kathrin H.
