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Diet and external morphology of nine species of insectivorous bats from Zambia East Africa, were compared using multivariate methods. Morphological and dietary resemblance between spe_cies were positively correlated; that is, taxa which resembled each other most strongly morphol?g!cally were also most similar in dietary intake. The degree of morphological and dietary distinctiveness of a ~pecies_ was posi~ivel~ c_orrelated with its morphological and dietary variability. For exa_mple,_ spec1es wh1ch ~re qmte d1stmct from others in morphology or diet tend also to be quite v~nable m _those two attnbutes. Morphology of the bats was strongly predictive of their diets; most d1etary vanance _was accounted for by morphological variance, and the first morphological principal compone_nt predicted the presence in the diet of Lepidoptera, beetles, and Orthoptera with a high !eve! ~f s1gmfican~e. These results led to a model of community organization for closely related species m wh1ch a relatively large number of specialists with invariant attributes are clustered near the community cen~roid and a smaller number of distinctive, variable species occupy niches more distant from the centrmd.

Disuse typically causes an imbalance in bone formation and bone resorption, leading to losses of cortical and trabecular bone. In contrast, bears maintain balanced intracortical remodeling and prevent cortical bone loss during disuse (hibernation). Trabecular bone, however, is more detrimentally affected than cortical bone in other animal models of disuse. Here we investigated the effects of hibernation on bone remodeling, architectural properties, and mineral density of grizzly bear (Ursus arctos horribilis) and black bear (Ursus americanus) trabecular bone in several skeletal locations. There were no differences in bone volume fraction or tissue mineral density between hibernating and active bears or between pre- and post-hibernation bears in the ilium, distal femur, or calcaneus. Though indices of cellular activity level (mineral apposition rate, osteoid thickness) decreased, trabecular bone resorption and formation indices remained balanced in hibernating grizzly bears. These data suggest that bears prevent bone loss during disuse by maintaining a balance between bone formation and bone resorption, which consequently preserves bone structure and strength. Further investigation of bone metabolism in hibernating bears may lead to the translation of mechanisms preventing disuse induced bone loss in bears into novel treatments for osteoporosis.

Disuse typically uncouples bone formation from resorption, leading to bone loss which compromises bone mechanical properties and increases the risk of bone fracture. Previous studies suggest that bears can prevent bone loss during long periods of disuse (hibernation), but small sample sizes have limited the conclusions that can be drawn regarding the effects of hibernation on bone structure and strength in bears. Here we quantified the effects of hibernation on structural, mineral, and mechanical properties of black bear (Ursus americanus) cortical bone by studying femurs from large groups of male and female bears (with wide age ranges) killed during pre-hibernation (fall) and posthibernation (spring) periods. Bone properties that are affected by body mass (e.g. bone geometrical properties) tended to be larger in male compared to female bears. There were no differences (p > 0.226) in bone structure, mineral content, or mechanical properties between fall and spring bears. Bone geometrical properties differed by less than 5% and bone mechanical properties differed by less than 10% between fall and spring bears. Porosity (fall: 5.5 ± 2.2%, spring: 4.8 ± 1.6%) and ash fraction (fall: 0.694 ± 0.011, spring: 0.696 ± 0.010) also showed no change (p > 0.304) between seasons. Statistical power was high (>72%) for these analyses. Furthermore, bone geometrical properties and ash fraction (a measure of mineral content) increased with age and porosity decreased with age. These results support the idea that bears possess a biological mechanism to prevent disuse and age-related osteoporoses.

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