Functional Morphology and Masticatory Biomechanics of British Red Squirrels

British red squirrels Sciurus vulgaris exist in fragmented populations, with the spread of
invasive grey squirrels Sciurus carolinensis the leading cause. Populations are isolated,
occupying different habitats, consuming different diets and little genetic exchange occurring between them. As such, the potential for rapid evolution in the masticatory apparatus is high.
Here, I examine populations of British red squirrels for morpho-functional differences in the masticatory apparatus, while also assessing the mechanical challenges of their diets.
In Chapter 2, I use geometric morphometrics to analyse the cranial and mandibular
morphology of four populations of British red squirrels. Variation between populations is
revealed, with specimens collected from Formby in the 1990s exhibiting morphological traits suggestive of lesser mechanical abilities of the masticatory apparatus.
In Chapter 3, I employ a novel method to gather data on the material properties of commonly consumed food items. Values of toughness, force to fracture and energy to fracture allows comparisons between food items. It is revealed that the diet of the Formby 1990s population, mostly peanuts, a supplementary food item provided by conservationists, poses a lesser mechanical challenge compared to other food items. A diet of deciduous nuts, like that of squirrels in Northern England, proved the most mechanically challenging. Chapter 4 attempts to assess the functional abilities conferred by morphological differences revealed in Chapter 2, by assessing biomechanical performance under loading through finite element analysis. This reveals a complicated picture where some models show some ability to perform well under stress and strain, as expected, but despite morphology adapted towards a softer diet, that Formby squirrels still maintain functional abilities. This thesis assesses the effects on the masticatory apparatus of British red squirrels using a three-pronged approach, revealing how isolation, fragmentation and provision of supplementary foods can influence the morphology, and potential survival, of this native species.