Danet Alain, Kéfi Sonia, Meneses Rosa I, Anthelme Fabien
AMAP CIRAD IRD CNRS INRA Université de Montpellier Montpellier France.
ISEM CNRS Université de Montpellier, IRD EPHEMontpellier France.
Ecol Evol. 2017 Dec 5;7(24):11265-11276. doi: 10.1002/ece3.3537. eCollection 2017 Dec.
Facilitation among plants mediated by grazers occurs when an unpalatable plant extends its protection against grazing to another plant. This type of indirect facilitation impacts species coexistence and ecosystem functioning in a large array of ecosystems worldwide. It has nonetheless generally been understudied so far in comparison with the role played by direct facilitation among plants. We aimed at providing original data on indirect facilitation at the community scale to determine the extent to which indirect facilitation mediated by grazers can shape plant communities. Such experimental data are expected to contribute to refining the conceptual framework on plant-plant-herbivore interactions in stressful environments. We set up a 2-year grazing exclusion experiment in tropical alpine peatlands in Bolivia. Those ecosystems depend entirely on a few, structuring cushion-forming plants (hereafter referred to as "nurse" species), in which associated plant communities develop. Fences have been set over two nurse species with different strategies to cope with grazing (direct vs. indirect defenses), which are expected to lead to different intensities of indirect facilitation for the associated communities. We collected functional traits which are known to vary according to grazing pressure (LDMC, leaf thickness, and maximum height), on both the nurse and their associated plant communities in grazed (and therefore indirect facilitation as well) and ungrazed conditions. We found that the effect of indirectly facilitated on the associated plant communities depended on the functional trait considered. Indirect facilitation decreased the effects of grazing on species relative abundance, mean LDMC, and the convergence of the maximum height distribution of the associated communities, but did not affect mean height or cover. The identity of the nurse species and grazing jointly affected the structure of the associated plant community through indirect facilitation. Our results together with the existing literature suggest that the "grazer-nurse-beneficiary" interaction module can be more complex than expected when evaluated in the field.
当一种适口性差的植物将其对放牧的防护扩展到另一种植物时，就会发生食草动物介导的植物间促进作用。这种间接促进作用影响着全球大量生态系统中的物种共存和生态系统功能。然而，与植物间直接促进作用所起的作用相比，到目前为止，它总体上一直未得到充分研究。我们旨在提供社区尺度上间接促进作用的原始数据，以确定食草动物介导的间接促进作用能够塑造植物群落的程度。此类实验数据有望有助于完善压力环境下植物 - 植物 - 食草动物相互作用的概念框架。我们在玻利维亚的热带高山泥炭地开展了一项为期两年的放牧排除实验。这些生态系统完全依赖于少数形成垫状结构的植物（以下简称“护株”物种），相关植物群落就在这些护株中发育。我们针对两种具有不同应对放牧策略（直接防御与间接防御）的护株物种设置了围栏，预计这会导致相关群落的间接促进作用强度不同。我们收集了已知会随放牧压力而变化的功能性状（叶干物质含量、叶片厚度和最大高度），这些性状来自放牧（以及由此产生的间接促进作用）和未放牧条件下的护株及其相关植物群落。我们发现，间接促进作用对相关植物群落的影响取决于所考虑的功能性状。间接促进作用降低了放牧对物种相对丰度、平均叶干物质含量以及相关群落最大高度分布趋同的影响，但不影响平均高度或盖度。护株物种的身份和放牧通过间接促进作用共同影响相关植物群落的结构。我们的研究结果与现有文献共同表明，在实地评估时，“食草动物 - 护株 - 受益者”相互作用模块可能比预期的更为复杂。
