School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, South Africa.
Proc Biol Sci. 2012 Jun 22;279(1737):2433-41. doi: 10.1098/rspb.2011.2472. Epub 2012 Feb 15.
Longitudinal studies have revealed how variation in resource use within consumer populations can impact their dynamics and functional significance in communities. Here, we investigate multi-decadal diet variations within individuals of a keystone megaherbivore species, the African elephant (Loxodonta africana), using serial stable isotope analysis of tusks from the Kruger National Park, South Africa. These records, representing the longest continuous diet histories documented for any extant species, reveal extensive seasonal and annual variations in isotopic--and hence dietary--niches of individuals, but little variation between them. Lack of niche distinction across individuals contrasts several recent studies, which found relatively high levels of individual niche specialization in various taxa. Our result is consistent with theory that individual mammal herbivores are nutritionally constrained to maintain broad diet niches. Individual diet specialization would also be a costly strategy for large-bodied taxa foraging over wide areas in spatio-temporally heterogeneous environments. High levels of within-individual diet variability occurred within and across seasons, and persisted despite an overall increase in inferred C(4) grass consumption through the twentieth century. We suggest that switching between C(3) browsing and C(4) grazing over extended time scales facilitates elephant survival through environmental change, and could even allow recovery of overused resources.
纵向研究揭示了消费者群体内部资源利用的变化如何影响它们在群落中的动态和功能意义。在这里，我们使用来自南非克鲁格国家公园的象牙的串联稳定同位素分析来研究关键巨型草食动物物种——非洲象（Loxodonta africana）个体内的多十年饮食变化。这些记录代表了任何现存物种记录的最长连续饮食史，揭示了个体的同位素——以及因此的饮食——生态位的广泛季节性和年度变化，但个体之间的变化很小。个体之间缺乏生态位差异与最近的几项研究形成对比，这些研究发现各种分类群的个体生态位专业化程度相对较高。我们的结果与理论一致，即个体哺乳动物食草动物在营养上受到限制，无法维持广泛的饮食生态位。对于在时空异质环境中广泛觅食的大型分类群来说，个体饮食专业化也是一种代价高昂的策略。个体饮食的可变性在季节内和季节之间都很高，并且尽管在 20 世纪整体推断的 C(4)草食摄入量增加，但仍然存在。我们认为，在长时间尺度上在 C(3)浏览和 C(4)放牧之间切换有助于大象通过环境变化生存，甚至可以允许过度使用的资源恢复。
