1. A negative relationship between water availability and the abundance of 15N relative to 14N (expressed as ?15N) in the bone collagen of herbivores has been widely reported. However, the relative importance of dietary ?15N and animal metabolism in producing this effect remains unclear. 2. To evaluate the relative importance of these two factors, we examined variation in ?15N of both grass foliage and kangaroo (Macropus spp.) bone collagen. We assessed whether the offset between grass and bone collagen ?15N was constant with respect to water availability. 3. An index of water availability (annual actual evapotranspiration/annual potential evapotranspiration) explained a considerable proportion of the variation in both grass ?15N (R2 = 0.40) and bone collagen ?15N (R2 = 0.57), and the slopes of these negative relationships were similar, with a near-constant ?15N offset between grass foliage and bone collagen. 4. This finding suggests that dietary ?15N is the main cause of the negative relationship between kangaroo bone collagen ?15N and water availability, with metabolic factors having little discernible effect. � 2006 The Authors.
|Number of pages||8|
|Publication status||Published - 2006|