Abstract
Closely related syntopic species have been shown to avoid competition by differentiating in the type of food they process. This can be achieved by changes in size or in the masticatory apparatus that produce modifications in bite force. The wood mouse (Apodemus sylvaticus (Linnaeus, 1758)) and Western Mediterranean mouse (Mus spretus Lataste, 1883) are two murid rodent species found in syntopy in the south of France. We measured bite force in wild specimens of both species to test for differences in performance. Despite its greater body mass, the wood mouse showed only slightly higher bite force than the Western Mediterranean mouse. We found no clear sexual dimorphism in either species; however, among the males of the Western Mediterranean mouse, two groups appeared in terms of bite force. This bite force difference may correspond to a hierarchical organization of these males. Overall, it seems that both species have similar bite forces and accordingly overlap in the resources they use. Other factors may exist that create a niche differentiation between the wood mouse and the Western Mediterranean mouse. Another explanation may be a great abundance of food, which would cancel competition for this resource in these species.