【作者】 储诚进；

【导师】 王刚；

【作者基本信息】 兰州大学 ， 生态学， 2010， 博士

【摘要】 生物间相互作用是生态学研究的核心内容,当前大部分生态学理论均建立在生物间负相互作用基础之上。然而,随着胁迫环境下大量野外工作的出现,研究人员发现生物间不仅存在竞争等负相互作用,而且还存在促进的正相互作用。如何将正相互作用融入主要以竞争为基础的生态学理论就成了生态学家们亟需解决的问题。本论文以此为出发点,结合计算机模拟、野外实验与统计推断等手段,系统探讨植物间正相互作用对种群动态与群落结构的影响,以期建立综合正负相互作用于一体的生态学理论框架。在青藏高原东缘高寒草甸地区,通过多物种邻体去除、多性状测量与多变量统计推断,发现在青藏高原高寒草甸恶劣生境下植物间正相互作用是广泛存在的,但不同物种、不同性状之间存在一定的差异,即正相互作用是物种特异与性状特异的；同时,局部微环境也对正相互作用的发生频率和强度施加影响。这为随后构建种群与群落模型、验证模型预测提供了基础。在单物种种群中,通过扩展著名的影响域模型建立了基于正负相互作用动态平衡的植物生长速率方程。模拟结果表明,正相互作用显著改变了种群的生物量—密度关系,即经典的恒定产量法则,提高了种群的个体大小不整齐性。高寒草甸地区垂穗披碱草种植实验支持了模型的预测：在中等密度水平下平均个体生物量最大而种群的个体大小不整齐性最小。同时,理论模拟还发现胁迫环境本身减小了自疏斜率(负值,即绝对值增大),而正相互作用则能够缓解胁迫条件对自疏轨迹的影响,即增大自疏斜率(负值,即绝对值减小)。上述结果表明,正相互作用对种群动态的作用不可忽视,尤其是在相对胁迫的生境条件下。基于物种差异、生态位—中性连续体及正相互作用物种特异性的认识,将生物间正相互作用引入Lin等(2009)出生—死亡权衡的中性模型,结果表明一定强度的正相互作用可以显著增长两物种群落的共存时间,提高多物种群落的物种丰富度。高寒与亚高寒草甸地区物种丰富度沿海拔梯度的分布模式与该理论结果相一致,即单位面积内高寒植物群落的物种数目明显高于亚高寒草甸群落的物种数目。Klein等(2004)增温实验从侧面支持了模型的假定与预测,这意味着改变高寒生境的全球变暖所导致的正相互作用强度减弱甚至消失将会对脆弱生态系统如高寒草甸产生灾难性的影响,加速生物多样性的丧失。由此可见,植物间正相互作用对种群动态与群落结构具有重要的影响,构建基于正负两种相互作用的生态学理论势在必行。在全球气候变化的大背景下,该研究具有重要的理论与现实意义。更多还原

【Abstract】 The study of biotic interactions among organisms has been one of the most critical issues in community ecology during the last decades. The majority of current ecological theories on plant community structure and dynamics are permeated with negative interactions (i.e. competition). However, many experiments conducted in the last 20 years, especially conducted in physically harsh environments, have demonstrated that positive interactions (i.e. facilitation) also play an essential role in natural systems. How to incorporate facilitation into mainstream ecological theories mainly based on competition has been an emerging task for ecologists. By combining field experiments, model simulations and statistical inference, the present dissertation explores the potential effects of positive interactions among plants on population dynamics and community structures, and attempts to construct a holistic theoretical framework accounting for both facilitation and competition.Using two constrasted sites, six species, and five plant traits, we exploited the effects of the various factors on the outcome of plant interactions in an alpine meadow of the Qinghai-Tibetan Plateau. The results demonstrated that the responses to the removal of neighbors were species-and trait-specific, as well as the local environmental conditions. These experiments shed light upon the assumptions and prediction tests of population and community models we constructed.By using an extended version of an individual-based’Zone-Of-Influence’model, we constructed grow-rate equations for individual plants in monoculture to test the hypothesis that the balance between facilitative and competitive interactions determined biomass-density relationships (i.e. constant final yield), size inequality and self-thinning trajectories. Our results showed that positive interactions profoundly affect biomass-density relationships, and increase the size inequality of model populations with and without density-dependent mortality. The modelling results were supported by field experiments, in which the greatest individual and the lowest size inequality of E. nutans populations were found at intermediate densities in a high-stress alpine habitat. Additionally, facilitation ameliorated the impact of the abiotic environment per se on. the allometric slopes, which significantly sharpened the self-thinning trajectory for survivors. All these results emphasized that positive interactions among individuals could be another key factor to determine plant population dynamics.With the recognition of species difference, niche-neutrality continuum and species-specific facilitation in mind, based on recently developed tradeoff-based neutral models of Lin et al. (2009), we elucidated the potential effects of facilitative interactions on the spatial distribution of species richness along an elevation gradient. The results illustrated that facilitation could improve the time of coexistence in two-species systems, and greatly increase the number of species in multiple-species systems. The results from field experiments conducted in alpine and subalpine meadows agreed with those from simulation patterns:the number of species in an alpine meadow was higher than that found in a subalpine meadow. Results from warming experiments, such as that of Klein et al. (2004), are in line with those from our simulations, implying that the alleviation of temperature limitation expected under global warming could destroy the interaction webs among plants, resulting in a sharp decline of species richness, especially in fragile ecosystems such as alpine meadows.Taken together, we conclude that facilitation among individuals could be an important factor in shaping population dynamics and community structures. In the context of global climate change, it is imperative to include positive interactions into mainstream ecological theories. This will facilitate the development of new theories and conceptual models, as well as the establishment of sound management actions.更多还原