Morphological changes in a British mammal as a result of introductions and changes in landscape management: the red squirrel (Sciurus vulgaris)

Abstract

British red squirrel populations have been subject to landscape management practices resulting in large-scale fragmentation and defragmentation of habitat, as well as numerous historical introductions of closely related subspecies. This unique population history allowed us to examine: (1) the morphological changes to a rare native species probably caused by hybridization with introduced subspecies; (2) the impact of landscape management, specifically reforestation, on the spread of these morphological changes across the north of England. British red squirrels represent a peripheral population of Sciurus vulgaris, which is regarded as a separate subspecies (S. v. leucourus) to populations found on the European continent. British populations are in danger of extinction because of the introduction of the North American grey squirrel S. carolinensis. Repeated translocation of continental European S. vulgaris individuals to Britain over 150 years may be responsible for an alteration of the morphological characteristics of populations compared to the original subspecies description. The majority of examined populations possessed the coat colour characteristics associated with continental European subspecies. Only populations in the western region of Cumbria possessed coat colour characteristics similar to the described subspecies S. v. leucourus. Changes to landscape connectivity in Britain during the 1980s greatly altered dispersal patterns, resulting in an increase of gene flow from populations in the north-east of England and the Borders into Cumbria. The morphological characteristics of the Cumbrian population also changed over this period, from traits similar to the British subspecies before 1980, to traits similar to the continental European subspecies after 1980. This study demonstrates the threat landscape management practices and the introduction of closely related subspecies can present to rare peripheral populations.