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Abstract

The stable carbon isotopic composition (expressed as d13C) of herbivore remains is commonly used to reconstruct past
changes in the relative abundance of C4 versus C3 grass biomass (C4 relative abundance). However, the strength of the relationship
between herbivore d13C and C4 relative abundance in extant ecosystems has not been thoroughly examined. We
determined sources of variation in d13C of bone collagen and tooth enamel of kangaroos (Macropus spp.) collected throughout
Australia by measuring d13C of bone collagen (779 individuals) and tooth enamel (694 individuals). An index of seasonal
water availability, i.e. the distribution of rainfall in the C4 versus C3 growing seasons, was used as a proxy for C4 relative
abundance, and this variable explained a large proportion of the variation in both collagen d13C (68%) and enamel d13C
(68%). These figures increased to 78% and 77%, respectively, when differences between kangaroo species were accounted
for. Vegetation characteristics, such as woodiness and the presence of an open forest canopy, had no effect on collagen or
enamel d13C. While there was no relationship between collagen d13C and kangaroo age at death, tooth enamel produced later
in life, following weaning, was enriched in 13C by 3.5‰ relative to enamel produced prior to weaning. From the observed
relationships between seasonal water availability and collagen and enamel d13C, enrichment factors (e*) for collagen-diet
and enamel-diet (post-weaning) were estimated to be 5.2‰± 0.5 (95% CI) and 11.7‰ ± 0.6 (95% CI), respectively. The findings
of this study confirm that at a continental scale, collagen and enamel d13C of a group of large herbivores closely reflect C4
relative abundance. This validates a fundamental assumption underpinning the use of isotopic analysis of herbivore remains
to reconstruct changes in C4 relative abundance.

Item Type:	Article
Authors/Creators:	Murphy, BP and Bowman, DMJS and Gagan, MK
Journal or Publication Title:	Geochimica et Cosmochimica Acta
Publisher:	Pergamon
ISSN:	0016-7037
DOI / ID Number:	10.1016/j.gca.2007.05.012
Additional Information:	The definitive version is available at http://www.sciencedirect.com
Item Statistics:	View statistics for this item

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