Data from: A stoichiometric perspective of the effect of herbivore dung on ecosystem functioning

Ungulate herbivores play a prominent role in maintaining the tree–grass balance in African savannas. Their top-down role through selective feeding on either trees or grasses is well studied, but their bottom-up role through deposition of nutrients in dung and urine has been overlooked. Here, we propose a novel concept of savanna ecosystem functioning in which the balance between trees and grasses is maintained through stoichiometric differences in dung of herbivores that feed on them. We describe a framework in which N2-fixing trees and grasses, as well as ungulate browsing and grazing herbivores, occupy opposite positions in an interconnected cycle of processes. The framework makes the testable assumption that the differences in dung N:P ratio among browsers and grazers are large enough to influence competitive interactions between N2-fixing trees and grasses. Other key elements of our concept are supported with field data from a Kenyan savanna.

有蹄类草食动物在维持非洲稀树草原的树-草平衡中发挥着关键作用。学界已对其通过选择性取食树木或草本植被所产生的下行调控效应开展了充分研究，但它们通过粪便与尿液沉积养分所介导的上行调控效应却长期被忽视。本文提出了一种全新的稀树草原生态系统功能概念，即通过取食不同植被类群的草食动物粪便的化学计量特征差异，实现树木与草本植物的平衡维持。我们构建了一个理论框架，其中固氮树木、草本植物，以及执行啃食（取食木本植物）和放牧（取食草本植物）策略的有蹄类草食动物，在相互关联的过程循环中占据对立的生态位位置。该框架提出了一项可检验假说：啃食者与放牧者的粪便氮磷（N:P）比值差异足够显著，足以影响固氮树木与草本植物之间的种间竞争关系。该概念的其他核心要素均得到了来自肯尼亚稀树草原的野外实地数据的支撑。