Abstract
Models of herbivore diversification rely heavily on adaptations that reflect the nutritional quality of foods consumed. In particular, browsers and grazers are expected to show dichotomous adaptations to deal with high quality (concentrate) browse-based and poor quality grass-based diets, respectively. In this study, we test the widespread assumption that browse represents a higher quality food source than grass. We analyzed plants from a South African savanna, collected over one dry and one wet season across several habitat types, for percent nitrogen (%N), neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) to compare variations in nutritional value of different food types. Results show consistently higher %N and lower NDF and ADF of tree foliage and forbs compared to monocots, but the former have consistently higher ADL, implying a higher fiber digestibility in grass compared with browse. Some fruit species have a high NDF and ADL content, implying poorer nutritional value than is commonly assumed. Our findings are in agreement with several other studies depicting relatively poor digestibility of browse (tree foliage and fruit) compared to grass. Reference to browse as high quality foods is therefore misleading, and models of herbivory that rest on this assumption require revision. The more efficient fiber digestibility recorded in grazers compared to browsers cannot be treated as an adaptation to poor quality diets, but rather to maximize benefits of higher fiber digestibility of grass. Spatio-seasonal variations in plant nutritional seem to reflect seasonal and spatial diet changes expected for grazers and intermediate (mixed) feeders. We propose that future studies require further detail on variations in diet, diet quality, and digestive efficiency to properly understand mechanisms of adaptation.
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Acknowledgements
We thank Darryl de Ruiter, Todd Robinson, James Brink, and Norman Owen-Smith for advice and comments on the study; Charles T. Robbins for commenting on an earlier draft of this manuscript; and Marcus Clauss and an anonymous reviewer for thorough efforts that greatly improved the clarity of the paper. We also thank Rina Grant, Angela Gaylard, Abri de Buys, and Wilson Dinda for facilitating and assisting with research in Kruger National Park; the Limpopo Tourism and Parks Board for access to Hans Merensky Nature Reserve; Carl Morrow and Jo Crane for facilitating fiber analyses; John Lanham and Ian Newton for assistance with mass spectrometry; and Nick Zambatis (Kruger Park) and the South African Weather Bureau for climate data. Funding was provided by the Palaeontological Scientific Trust (RSA), the National Research Foundation (RSA), the National Science Foundation (USA), and the University of Cape Town (RSA).
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Codron, D., Lee-Thorp, J.A., Sponheimer, M. et al. Nutritional content of savanna plant foods: implications for browser/grazer models of ungulate diversification. Eur J Wildl Res 53, 100–111 (2007). https://doi.org/10.1007/s10344-006-0071-1
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DOI: https://doi.org/10.1007/s10344-006-0071-1