1. A negative relationship between water availability and the abundance of 15N relative to 14N (expressed as δ15N) in the bone collagen of herbivores has been widely reported. However, the relative importance of dietary δ15N and animal metabolism in producing this effect remains unclear. 2. To evaluate the relative importance of these two factors, we examined variation in δ15N of both grass foliage and kangaroo (Macropus spp.) bone collagen. We assessed whether the offset between grass and bone collagen δ15N 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 δ15N (R2 = 0.40) and bone collagen δ15N (R2 = 0.57), and the slopes of these negative relationships were similar, with a near-constant δ15N offset between grass foliage and bone collagen. 4. This finding suggests that dietary δ15N is the main cause of the negative relationship between kangaroo bone collagen δ15N and water availability, with metabolic factors having little discernible effect. © 2006 The Authors.

Item Type:	Refereed Article
Research Division:	Biological Sciences
Research Group:	Other Biological Sciences
Research Field:	Global Change Biology
Objective Division:	Environment
Objective Group:	Climate and Climate Change
Objective Field:	Social Impacts of Climate Change and Variability
Author:	Bowman, DMJS (Professor David Bowman)
ID Code:	46470
Year Published:	2006
Web of Science® Times Cited:	86
Deposited By:	Plant Science
Deposited On:	2007-09-19
Last Modified:	2011-06-22
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