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Using carbon isotope analysis of the diet of two introduced Australian megaherbivores to understand Pleistocene megafaunal extinctions

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Abstract:

Abstract Aim 

Australia lost a diverse assemblage of large marsupial herbivores in the late Pleistocene, with suggestions that the extinctions were biased towards browsers. In modern times two bovines, the Asian water buffalo (Bubalus bubalis) and banteng (Bos javanicus), have established feral populations in the Northern Territory, Australia. Buffalo have aggressively expanded throughout the savanna landscape, yet banteng remain near their point of introduction on the Cobourg Peninsula. We hypothesized that this difference is related to feeding ecology, possibly reflecting a legacy of the Pleistocene extinctions. Location 

Western Arnhem Land, Northern Territory, Australia. Methods 

Analysing a previously published dataset of body mass and feeding ecology of extinct and extant marsupial herbivores, we evaluated whether browsers were at greater risk of extinction than grazers. We compared the carbon isotope composition and nitrogen content of banteng and buffalo dung in order to evaluate the hypotheses that the differences in invasion success are related to feeding ecology, and that seasonal variation in browse consumption is linked to changing nutritional quality of grass. Results 

Controlling for body mass, the Pleistocene extinctions were clearly biased towards browsers. Introduced banteng appear to be primarily browsers, with their diets comprising 40% grass in the wet season and 15% in the late dry season. Buffalo have a more variable diet, with an increasing proportion of browse from the wet (30%) to the late dry season (75%), and can therefore be described as switching from grazer to browser. The decline of grass in the diet of both species appears to reflect the decline in the nutritional value of grass through the dry season, an inference supported by the negative relationship between δ13C values and the nitrogen content of dung. Main conclusions 

Banteng and buffalo are much larger than extant native herbivores, of which browsers are restricted to isolated rocky habitats. This suggests that banteng and buffalo have filled niches made vacant following the Pleistocene extinctions. The success of buffalo appears to be related to their greater dietary breadth, which enables them to graze and browse in eucalypt savannas, whilst the browsing banteng remain tethered to a mosaic of rain forest patches. The restriction of browsers may be a long-range consequence of habitat transformations associated with Aboriginal landscape burning.

Keywords: Aboriginal landscape burning; Asian water buffalo; banteng; feeding ecology; feral animals; foraging plasticity; invasion biology; late Pleistocene extinctions; megafauna; stable isotope analysis

Document Type: Research Article

DOI: http://dx.doi.org/10.1111/j.1365-2699.2009.02206.x

Affiliations: 1: School of Plant Science, University of Tasmania, Hobart, Tas. 7001, Australia 2: School for Environmental Research, Institute for Advanced Studies, Charles Darwin University, Darwin, NT 0909, Australia

Publication date: March 1, 2010

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