Sustainable coexistence of similar, related species is generally expected to be achieved through character displacement, resulting in niche partitioning. The species Apodemus sylvaticus and Apodemus flavicollis are very similar both morphologically and ecologically, and have a large geographical overlap. Whether functional or biomechanical differences between these two species contribute to their coexistence remains unknown. A biomechanical model was created based on muscle data derived from dissections to estimate the maximum bite force. In addition, the dental microwear was analysed to test for evidence of a divergence in diet. Finally, geometric morphometric approaches were used to compare mandibular shapes. The results indicate that A. flavicollis, the slightly larger species, is optimized for biting at a larger gape angle. Apodemus sylvaticus appears to be slightly more specialized for grinding and biting at a narrower gape angle. However, the majority of shape variation in the mandible across both species follows the same pattern. No significant differences in microwear were observed between species, and thus, they appear to consume similar food types. These results suggest that character divergence resulting in niche partitioning has not occurred, possibly due to low resource competition. Alternatively, resource partitioning may occur through behavioural differences or differences in activity patterns.

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