Soliveres Santiago, Eldridge David J, Maestre Fernando T, Bowker Matthew A, Tighe Matthew, Escudero Adrián
Área de Biodiversidad y Conservación, Departamento de Biología y Geología, Escuela Superior de Ciencias Experimentales y Tecnología, Universidad Rey Juan Carlos, 28933 Móstoles, Spain ; Instituto de Recursos Naturales, Centro de Ciencias Medioambientales, C.S.I.C., Serrano 115, E-28006 Madrid, Spain.
Office of Environment and Heritage, Department of Premier & Cabinet, c/- Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
Perspect Plant Ecol Evol Syst. 2011 Nov 20;13(4):247-258. doi: 10.1016/j.ppees.2011.06.001.
Studies of facilitative interactions as drivers of plant richness along environmental gradients often assume the existence of an overarching stress gradient equally affecting the performance of all the species in a given community. However, co-existing species differ in their ecophysiological adaptations, and do not experience the same stress level under particular environmental conditions. Moreover, these studies assume a unimodal richness-biomass curve, which is not as general as previously thought. We ignored these assumptions to assess changes in plant-plant interactions, and their effect on local species richness, across environmental gradients in semi-arid areas of Spain and Australia. We aimed to understand the relative importance of direct (microhabitat amelioration) and indirect (changes in the competitive relationships among the understorey species: niche segregation, competitive exclusion or intransitivity) mechanisms that might underlie the effects of nurse plants on local species richness. By jointly studying these direct and indirect mechanisms using a unifying framework, we were able to see how our nurse plants (trees, shrubs and tussock grasses) not only increased local richness by expanding the niche of neighbouring species, but also by increasing niche segregation among them, though the latter was not important in all cases. The outcome of the competition-facilitation continuum changed depending on the study area, likely because the different types of stress gradient considered. When driven by both rainfall and temperature, or rainfall alone, the community-wide importance of nurse plants remained constant (Spanish sites), or showed a unimodal relationship along the gradient (Australian sites). This study expands our understanding of the relative roles of plant-plant interactions and environmental conditions as drivers of local species richness in semi-arid environments. These results can also be used to refine predictions about the response of plant communities to environmental change, and to clarify the relative importance of biotic interactions as a driver of such responses.
将促进性相互作用作为沿环境梯度驱动植物丰富度的因素进行研究时，通常假定存在一个总体压力梯度，该梯度对给定群落中所有物种的表现产生同等影响。然而，共存物种在生态生理适应性方面存在差异，在特定环境条件下所经历的压力水平也不尽相同。此外，这些研究假定存在单峰的丰富度-生物量曲线，但实际情况并非像之前认为的那样普遍。我们忽略了这些假设，以评估西班牙和澳大利亚半干旱地区沿环境梯度的植物间相互作用变化及其对当地物种丰富度的影响。我们旨在了解直接机制（微生境改善）和间接机制（下层物种间竞争关系的变化：生态位分离、竞争排斥或非传递性）的相对重要性，这些机制可能是护植物对当地物种丰富度产生影响的潜在原因。通过使用统一框架联合研究这些直接和间接机制，我们得以了解我们的护植物（树木、灌木和草丛）不仅通过扩大邻近物种的生态位增加了当地的丰富度，还通过增加它们之间的生态位分离来实现这一点，尽管后者在所有情况下并不都重要。竞争-促进连续体的结果因研究区域而异，这可能是由于所考虑的压力梯度类型不同。当由降雨和温度共同驱动，或仅由降雨驱动时，护植物在整个群落中的重要性保持不变（西班牙地区），或沿梯度呈现单峰关系（澳大利亚地区）。这项研究扩展了我们对植物间相互作用和环境条件作为半干旱环境中当地物种丰富度驱动因素的相对作用的理解。这些结果还可用于完善关于植物群落对环境变化响应的预测，并阐明生物相互作用作为这种响应驱动因素的相对重要性。
