Ejrnaes Rasmus, Bruun Hans Henrik, Graae Bente J
Department of Wildlife Ecology and Biodiversity, National Environmental Research Institute, Rønde, Denmark.
Ecology. 2006 May;87(5):1225-33. doi: 10.1890/0012-9658(2006)87[1225:caiegs]2.0.co;2.
It is hard to defend the view that biotic communities represent a simple and predictable response to the abiotic environment. Biota and the abiotic environment interact, and the environment of an individual certainly includes its neighbors and visitors in the community. The complexity of community assembly calls forth a quest for general principles, yet current results and theories on assembly rules differ widely. Using a grassland microcosm as a model system, we manipulated fertility, disturbance by defoliation, soil/microclimate, and arrival order of species belonging to two groups differing in functional attributes. We analyzed the outcome of community assembly dynamics in terms of species richness, invasibility, and species composition. The analyses revealed strong environmental control over species richness and invasibility. Species composition was mainly determined by the arrival order of species, indicating that historical contingency may change the outcome of community assembly. The probability for multiple equilibria appeared to increase with productivity and environmental stability. The importance of arrival order offers an explanation of the difficulties in predicting local occurrences of species in the field. In our experiment, variation in fertility and disturbance was controlling colonization with predictable effects on emergent community properties such as species richness. The key mechanism is suggested to be asymmetric competition, and our results show that this mechanism is relatively insensitive to the species through which it works. While our analyses indicate a positive and significant correlation between richness and invasibility, the significance disappears after accounting for the effect of the environment. The importance of arrival order (historical contingency) and environmental control supports the assumption of the unified neutral theory that different species within a trophic level can be considered functionally equivalent when it comes to community assembly. However, our results indicate that variation in asymmetric competition is the key factor determining the richness of the resulting communities, and this is far from neutral.
认为生物群落是对非生物环境的简单且可预测的反应，这种观点很难站得住脚。生物群落与非生物环境相互作用，个体所处的环境无疑包括其所在群落中的邻居和访客。群落组装的复杂性引发了对一般原则的探寻，但目前关于组装规则的研究结果和理论差异很大。我们以草地微观生态系统为模型系统，对肥力、通过去叶进行的干扰、土壤/微气候以及属于两个功能属性不同的组的物种的到达顺序进行了操控。我们从物种丰富度、可入侵性和物种组成方面分析了群落组装动态的结果。分析揭示了环境对物种丰富度和可入侵性有很强的控制作用。物种组成主要由物种的到达顺序决定，这表明历史偶然性可能会改变群落组装的结果。多重平衡的概率似乎随着生产力和环境稳定性的增加而上升。到达顺序的重要性解释了在野外预测物种局部出现情况时所面临的困难。在我们的实验中，肥力和干扰的变化控制着群落定植，并对诸如物种丰富度等群落涌现特性产生可预测的影响。关键机制被认为是不对称竞争，我们的结果表明该机制对其起作用的物种相对不敏感。虽然我们的分析表明丰富度和可入侵性之间存在正相关且显著相关，但在考虑环境影响后这种相关性就消失了。到达顺序（历史偶然性）和环境控制的重要性支持了统一中性理论的假设，即就群落组装而言，营养级内的不同物种在功能上可被视为等效。然而，我们的结果表明，不对称竞争中的变化是决定最终群落丰富度的关键因素，而这远非中性。
