A search for age-related changes in bite force and diet in shrews

Tooth attrition is rapid and extensive in soricine shrews. Seemingly, without compensatory morphological changes to increase bite force, older individuals must shift their diet to softer items and risk greater overlap with trophic niches of more numerous younger individuals of syntopic taxa with lower relative bite force. Initial tests of this hypothesis indicated that neither efficiency of jaw mechanics nor mass of the masticatory muscles increased significantly with age (as indexed by length of 11) in 101 Sorer trowbridgii. Similar tests of changes in these characters and hardness of the diet with age for samples of several taxa were inconclusive; coefficients of correlation were significant for a few of the relationships tested. However, a meta-analysis technique for combining coefficients of correlation to test the consensus of sets of independent tests addressing common null hypotheses indicated that overall efficiency of jaw mechanics in western shrews (Sorer) increased significantly with age: Reduction of the length of the resistance moment arm (condyloid-il length) with age contributed most to the jaw mechanics-age relationship. Although the mechanism by which the jaw shortens remains unclear, the effect likely is sufficient to prevent a significant increase in age-related overlap of trophic niches of syntopic species of western shrews.