When a species is introduced to a new area, it often can have detrimental effects on the native ecosystem. The causes of those negative impacts are often unknown. The grey squirrel from North America was introduced to Europe in ~1948 and has had devastating impacts on the native Eurasian red squirrel (pictured above). With our Italian collaborators Francesca Santicchia (Ph.D. student) and Prof. Luc Wauters at the University of Insubria and funding from the European Squirrel Initiative, we asked if the presence of grey squirrels induced stress in the native Eurasian red squirrel. Francesca and Luc used a really comprehensive set of experiments along with collection of fecal samples to show that the presence of invasive grey squirrels does substantially increase the stress hormone levels of the native Eurasian red squirrel and removal of the invasive grey squirrels can lower the stress levels of the native Eurasian red squirrel. Because elevated stress levels may suppress reproduction or lower survival, the presence of invasive grey squirrels may therefore negatively affect the native Eurasian red squirrel by increasing their stress levels. This work is now published in the Journal of Animal Ecology.
Photo credit and photo made available by CC BY 2.0