Nutritional content of savanna plant foods: implications for browser/grazer models of ungulate diversification |
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Authors: | Daryl Codron Julia A Lee-Thorp Matt Sponheimer Jacqui Codron |
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Institution: | (1) Department of Archaeology, University of Cape Town, Private Bag, Rondebosch, 7701, Republic of South Africa;(2) Florisbad Quaternary Research, National Museum, P.O. Box 266, Bloemfontein, 9300, Republic of South Africa;(3) Department of Archaeological Sciences, University of Bradford, Bradford, BD7 1DP, UK;(4) Department of Anthropology, University of Colorado at Boulder, Boulder, CO 80309, USA |
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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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Keywords: | Browse Diet quality Fiber Grass Protein |
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