One of the best strategies to help species cope with anthropogenic changes, such as climate change and habitat loss, is to promote connectivity between suitable habitats. By connecting patches with ecological corridors, species will have the opportunity to migrate if necessary. But connectivity, once established, is used by the species we intend to help, and those we don’t. This includes invasive species, which are able to use corridors to spread to new habitats and potentially continue to thrive in the face of climate change.
Across the globe, squirrels are very successful mammalian invaders. Despite being adorable, where they invade they cause harm, outcompeting native mammals, harming vegetation, and transmitting disease. In Italy there are four species of invasive squirrels – Sciurus carolinensis, Callosciurus finlaysonii, Callosciurus erythraeus, and Eutamias sibiricus. These species are all tree-dwelling, and rely on connectivity of forests to expand their ranges.
Using species distribution models and circuit theory methods, researchers determined if models using climate change alone, or climate change paired with habitat change estimates, yielded different results for the potential future distribution of these invasive species.
With just global warming alone, the ranges of these invasive squirrels is expected to increase across Italy, over 50% compared to current ranges. However, when projected land use changes are also considered, fewer dispersal corridors and less forested habitat are available to squirrels. Basically, warmer is good for squirrels but not good for squirrel habitat. Under these scenarios, there were predicted negative effects on all four species, leading to decreased range sizes and decreased population stability.
As the climate warms and ranges shift, managers looking to protect native species will need to include climate change in their decision making, yet as noted in a previous digest, climate change is rarely incorporated into connectivity mapping or planning. In addition to climate change, this study makes it clear that changes to land use also need to be considered; models that include climate change alone lead to very different outcomes than more complex models that take into consideration land use changes as well. This type of research is even more rare, however, because there are fewer projections available for land use change compared to projections for climate change.
It also means that ecological corridors are essential features for squirrel invasions, and their loss in the future is expected to harm both native and invasive species. For management, this research highlights the importance of preventing long-distance movement of squirrels to prevent jumps into unoccupied territory. Because squirrels are popular as pets and charismatic, this will involve the education of the public to prevent the sale and transport of these species.
Febbraro, MD, Menchetti, M, Russo, D, Ancillotto, L, Aloise, G, Roscioni, F, Preatoni, DG, Loy, A, Martinoli, A, Bertolino, S, Mori, E. (2019) Integrating climate and land‐use change scenarios in modelling the future spread of invasive squirrels in Italy. Diversity and Distributions, 25:644–659
Conservation Corridor Digest: Managing range shifts under climate change across new habitats and borders
Conservation Corridor Digest: Review: connectivity modeling for climate change