Department of Ecology and Evolutionary Biology, Brown University, Providence, RI, USA.
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, USA.
J Anim Ecol. 2020 Jun;89(6):1482-1496. doi: 10.1111/1365-2656.13206. Epub 2020 Apr 10.
Theory predicts that trophic specialization (i.e. low dietary diversity) should make consumer populations sensitive to environmental disturbances. Yet diagnosing specialization is complicated both by the difficulty of precisely quantifying diet composition and by definitional ambiguity: what makes a diet 'diverse'? We sought to characterize the relationship between taxonomic dietary diversity (TDD) and phylogenetic dietary diversity (PDD) in a species-rich community of large mammalian herbivores in a semi-arid East African savanna. We hypothesized that TDD and PDD would be positively correlated within and among species, because taxonomically diverse diets are likely to include plants from many lineages. By using DNA metabarcoding to analyse 1,281 faecal samples collected across multiple seasons, we compiled high-resolution diet profiles for 25 sympatric large-herbivore species. For each of these populations, we calculated TDD and PDD with reference to a DNA reference library for local plants. Contrary to our hypothesis, measures of TDD and PDD were either uncorrelated or negatively correlated with each other. Thus, these metrics reflect distinct dimensions of dietary specialization both within and among species. In general, grazers and ruminants exhibited greater TDD, but lower PDD, than did browsers and non-ruminants. We found significant seasonal variation in TDD and/or PDD for all but four species (Grevy's zebra, buffalo, elephant, Grant's gazelle); however, the relationship between TDD and PDD was consistent across seasons for all but one of the 12 best-sampled species (plains zebra). Our results show that taxonomic generalists can be phylogenetic specialists, and vice versa. These two dimensions of dietary diversity suggest contrasting implications for efforts to predict how consumers will respond to climate change and other environmental perturbations. For example, populations with low TDD may be sensitive to phylogenetically 'random' losses of food species, whereas populations with low PDD may be comparatively more sensitive to environmental changes that disadvantage entire plant lineages-and populations with low dietary diversity in both taxonomic and phylogenetic dimensions may be most vulnerable of all.
理论预测，营养特化（即低饮食多样性）应该使消费者种群对环境干扰敏感。然而，诊断特化既困难又复杂，因为精确量化饮食组成具有难度，而且定义也不明确：什么使饮食多样化？我们试图在东非半干旱稀树草原的一个大型哺乳动物食草动物物种丰富的群落中描述分类饮食多样性（TDD）和系统发育饮食多样性（PDD）之间的关系。我们假设 TDD 和 PDD 会在物种内和物种间呈正相关，因为分类多样化的饮食可能包括来自许多谱系的植物。通过使用 DNA 代谢组学分析在多个季节收集的 1281 个粪便样本，我们为 25 种共生的大型食草动物物种编制了高分辨率的饮食概况。对于这些种群中的每一个，我们都根据当地植物的 DNA 参考文库计算了 TDD 和 PDD。与我们的假设相反，TDD 和 PDD 的度量值要么不相关，要么相互负相关。因此，这些指标反映了物种内和物种间饮食特化的不同维度。一般来说，食草动物和反刍动物的 TDD 较高，但 PDD 较低，而食叶动物和非反刍动物则较低。我们发现除了四种物种（细纹斑马、水牛、大象、格兰特瞪羚）外，所有物种的 TDD 和/或 PDD 都有显著的季节性变化；然而，在 12 种采样最好的物种中，除了一种（平原斑马）外，TDD 和 PDD 之间的关系在所有季节都是一致的。我们的结果表明，分类上的多面手可能是系统发育上的专家，反之亦然。这两个饮食多样性维度表明，对于预测消费者如何应对气候变化和其他环境干扰的努力，有截然不同的影响。例如，TDD 低的种群可能对分类上“随机”的食物物种丧失敏感，而 PDD 低的种群可能对使整个植物谱系处于不利地位的环境变化更敏感——而在分类和系统发育维度上饮食多样性低的种群可能最脆弱。
