【作者】 王鑫厅；

【导师】 梁存柱； 王炜；

【作者基本信息】 内蒙古大学 ， 生态学， 2013， 博士

【摘要】 物种间相互作用的研究是生态学研究的核心。近年来,大量研究已经表明,正相互作用与负相互作用在群落中同时存在,只是在不同条件下,某一方将居主导作用。过度放牧引起的草原退化,集中体现在种群个体小型化上,而关于小型化的机理尚未有明确解释。那么,在放牧胁迫下,是否存在正相互作用与负相作用的转化?也就是说,过度放牧引起的草原退化能否纳入到正相互作用与负相互作用转化的生态学基本理论框架内?物种间的相互作用是影响种群格局特征的主要因素之一,如果在放牧胁迫下存在正相互作用与负相互作用的转化,那么,它将如何改变种群空间格局?本文以此为起点,选择典型草原带处于不同恢复演替阶段的群落,通过野外实验、统计模型等手段,探讨了在放牧胁迫下的正、负相互作用及其相互转化,分析正、负相互作用与草原退化过程中植物个体小型化的相关关系及其对种群空间格局的影响,以期以新的视角解释过度放牧引起的草原退化机理。这一研究对于认识由于过度放牧引发的草原退化具有一定的理论和现实意义。其主要研究结果如下：1.通过O-Ring函数计算并比较种群在不同尺度下的种群邻体密度,结果发现在不同放牧胁迫梯度下,存在正相互作用与负相互作用的转化,且这种转化主要发生在种内。在严重退化的群落中,正相互作用居主导,而在放牧胁迫较小的恢复群落中负相互作用占主导。2.过度放牧引起的严重退化群落,在正相互作用下,植物种群通过改变个体形态以抵御家畜的采食,改变分布状态来抵御家畜的践踏,改变形态和分布状态紧密联系在一起共筑了抵御采食和践踏的防线。进一步通过正相互作用理论解释了以往学者在试图解释小型化机理时所存在的不足,从而有力地说明了在过度放牧条件下所发生的植物个体小型化,当为在胁迫条件下种群正相作用所致,把草原退化(小型化)统一在物种间正相互作用的生态学基本理论框架内。3.在不同放牧胁迫梯度下,存在种内正相互作用与负相互作用的转化。通过点格局并结合完全空间随机模型、泊松聚块模型和嵌套双聚块模型,证明了在不同放牧胁迫梯度下正相互作用与负相互作用的转化引起种群空间格局发生变化。其实质是在正相互作用与负相互作用转化的过程中引发种群在局部小尺度范围内邻体密度发生变化所致。更多还原

【Abstract】 The investigation of interactions among plants has been a focus of ecology during last decades. Many studies in last20years have demonstrated that positive interaction may act simultaneously with competitive interaction in a community, and the over effect of interactions depends on which mechanism is the most important in a given environment. The temperate steppe of China has been heavily disturbed by overgrazing, which has resulted in serious degradation and characteristic vegetation patterns. The degraded community exhibited individual plant miniaturization. Miniaturized display show the following characteristics: shortened internodes, contracted leaf blades and a shallowly distributed root system. However, the mechanism of individual plant miniaturization has not been unlocked. Thus, Can the shift from facilitation to competition occur along gradients of grazing stress? In other words, can we incorporate the mechanisms of degradation in steppe into mainstream ecological theories based on the balance of facilitation and competition? A considerable challenge in plant ecology is to understand how interactions, such as competition or facilitation, shape the spatial distribution of plants. If facilitation and competition are balanced along gradients of grazing pressure, how does the balance between facilitation and competition affect spatial patterns? Choosing different restored successional communities in typical steppe and by combining field experiments and statistical models, the dissertation explores the effects of positive interactions on individual plant miniaturization and population spatial patterns under grazing stress among plants, and attempt to unlock mechanisms of degradation or miniaturization based on the theoretical framework of the balance of facilitation and competition. Using test statistics based on the univariate O-ring statistic to describe local density at different scales in different restored successional communities, the results show that facilitation is the dominant interaction in a seriously degraded community, and demonstrate that the shift from facilitation to competition along gradients of grazing stress are due to intraspecific interactions.Facilitation is the dominant interaction in a seriously degraded community. Under facilitation the plant populations defense strong grazing pressure by changing their morphology and distribution. The positive interaction theory can detect the mechanism of individual plant miniaturization, which further illustrate individual plant miniaturization is caused by facilitation in a seriously degraded community.Along gradients of grazing stress the shift of intraspecific interactions from facilitation to competition. By using point pattern analysis with different null models to detect the population spatial patterns in different restored successional communities, the results show the shift from facilitation to competition determine the spatial patterns in plant populations, which is caused by variation in small local density depending on the balance between facilitation and competition. Thus the mechanisms of degradation in typical steppe are incorporated into mainstream ecological theories based on the balance of facilitation and competition.In all, in a seriously degraded community positive interaction is the dominant interaction, and by facilitation theory we scientifically explain the mechanisms of individual plant miniaturization. This is valuable for us to cognize the degradation and restoration on the typical steppe.更多还原