Inventory and Monitoring Program, Rocky Mountain Network, National Park Service, Fort Collins, Colorado 80525, USA.
Ecology. 2010 Nov;91(11):3252-60. doi: 10.1890/09-1849.1.
Niche complementarity, in which coexisting species use different forms of a resource, has been widely invoked to explain some of the most debated patterns in ecology, including maintenance of diversity and relationships between diversity and ecosystem function. However, classical models assume resource specialization in the form of distinct niches, which does not obviously apply to the broadly overlapping resource use in plant communities. Here we utilize an experimental framework based on competition theory to test whether plants partition resources via classical niche differentiation or via plasticity in resource use. We explore two alternatives: niche preemption, in which individuals respond to a superior competitor by switching to an alternative, less-used resource, and dominant plasticity, in which superior competitors exhibit high resource use plasticity and shift resource use depending on the competitive environment. We determined competitive ability by measuring growth responses with and without neighbors over a growing season and then used 15N tracer techniques to measure uptake of different nitrogen (N) forms in a field setting. We show that four alpine plant species of differing competitive abilities have statistically indistinguishable uptake patterns (nitrate > ammonium > glycine) in their fundamental niche (without competitors) but differ in whether they shift these uptake patterns in their realized niche (with competitors). Competitively superior species increased their uptake of the most available N form, ammonium, when in competition with the rarer, competitively inferior species. In contrast, the competitively inferior species did not alter its N uptake pattern in competition. The existence of plasticity in resource use among the dominant species provides a mechanism that helps to explain the manner by which plant species with broadly overlapping resource use might coexist.
生态位互补性是指共存物种利用资源的不同形式，它被广泛用来解释生态学中一些最具争议的模式，包括多样性的维持以及多样性与生态系统功能之间的关系。然而，经典模型假设资源的专门化形式是不同的生态位，这显然不适用于植物群落中广泛重叠的资源利用。在这里，我们利用基于竞争理论的实验框架来检验植物是否通过经典的生态位分化或资源利用的可塑性来分配资源。我们探讨了两种替代方案：生态位抢占，即个体通过转向替代的、较少使用的资源来应对优势竞争者；以及优势可塑性，即优势竞争者表现出高度的资源利用可塑性，并根据竞争环境改变资源利用。我们通过在生长季节内测量有和没有邻居时的生长反应来确定竞争能力，然后在野外环境中使用 15N 示踪技术来测量不同氮（N）形式的吸收。我们表明，四种具有不同竞争能力的高山植物物种在其基本生态位（没有竞争者）中具有统计上不可区分的吸收模式（硝酸盐>铵>甘氨酸），但在其实现的生态位（有竞争者）中是否改变这些吸收模式方面存在差异。具有竞争优势的物种在与较稀少、竞争劣势的物种竞争时，增加了对最易获得的 N 形式铵的吸收。相比之下，竞争劣势的物种在竞争中并没有改变其 N 吸收模式。优势物种中资源利用的可塑性的存在提供了一种机制，有助于解释具有广泛重叠资源利用的植物物种如何共存。
