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, old er individuals must shift their diet to softer items and risk greater overlap with trophic niches of more numerous younger individuals of sy ntopic taxa with lower relative bite force. Initial tests of this hypo thesis indicated that neither efficiency of jaw mechanics nor mass of the masticatory muscles increased significantly with age (as indexed b y length of 11) in 101 Sorer trowbridgii. Similar tests of changes in these characters and hardness of the diet with age for samples of seve ral taxa were inconclusive; coefficients of correlation were significa nt for a few of the relationships tested. However, a meta-analysis tec hnique for combining coefficients of correlation to test the consensus of sets of independent tests addressing common null hypotheses indica ted that overall efficiency of jaw mechanics in western shrews (Sorer) increased significantly with age: Reduction of the length of the resi stance moment arm (condyloid-il length) with age contributed most to t he jaw mechanics-age relationship. Although the mechanism by which the jaw shortens remains unclear, the effect likely is sufficient to prev ent a significant increase in age-related overlap of trophic niches of syntopic species of western shrews.