【作者】 骆争荣；

【导师】 傅承新； 丁炳扬；

【作者基本信息】 浙江大学 ， 植物学， 2011， 博士

【摘要】 密度制约被认为是一种重要的维持森林物种多样性机制。40多年来,该理论受到广泛的关注和讨论。但对于其真正的作用仍存在很大的分歧,野外观测和实验研究得出了两方面的证据(支持或反对)。目前,对该理论的验证和研究仍然存在许多值得探讨的问题。例如密度制约在亚热带森林是否普遍,密度制约在不同物种、同一物种的不同生长阶段是否存在差异,密度制约到底能否影响群落的多样性。本文以浙江百山祖5ha亚热带常绿阔叶林固定监测样地两次调查数据为基础,从个体的存活率、种群的空间分布格局和群落的物种和谱系多样性三个层次分析密度制约对于亚热带中山常绿阔叶林森林动态的影响,探讨密度制约对于亚热带常绿阔叶林内物种多样性维持的作用。如果密度制约起作用,那么个体的存活将随个体周围的同种多度(或生物量)或进化上的近亲多度增高而下降；同时如果存在集群保护,那么个体将受周围异种的保护而增加存活。在控制个体大小、生境因素和空间自相关因素后,自相关逻辑斯蒂回归分析能够较好地反映个体存活与邻域内同种(或异种)多度或近缘种多度的关系,从而推断密度制约的作用。分析结果显示个体本身大小是影响其存活率的最主要因素,地形在一定成度上影响个体存活。在被监测的22个常见物种中,仅有8个物种的胸径1cm以上树木的存活受邻域内高同种密度或同种生物量的损害；增加邻域内的谱系复杂性仅显著提高2个物种的树木存活；增加邻域内的异种多度显著降低4个物种的个体存活,集群保护效应不存在。同种密度制约和谱系依赖的密度制约的强度和普遍性在幼苗阶段与后幼苗阶段没有显著差异。密度制约效应对不同的功能群的作用存在差异表明密度制约可能依赖于物种的功能特征。如果密度制约具有重要作用,那么种群的聚集程度将随年龄级(径级)的增大而下降(即密度制约的稀疏效应),后代的分布重心与母树的距离将随年龄的增大而增大(即密度制约的距离效应)。本研究使用点格局分析中的成对关联函数作为统计工具,选择异质性泊松过程和随机标签作为零模型控制大尺度上生境异质性对物种空间分布格局的影响,选择性的分析植物间的相互作用。结果表明53.3%的物种空间分布不受密度制约稀疏效应影响,对于受其影响的物种来说,这种效应对于种群空间格局的调节作用也不是一贯的,因此种群成年树并不能发展成为均匀格局。只有16.7%物种的未成年树在某个生长阶段远离成年树,密度制约的距离效应几乎不存在。而有63.3%的物种至少在一个阶段表现为非成年树向成年树靠拢,避难所效应起着更强的作用。由于多种因素共同作用,更新格局随生活史阶段在不断变化,并不能由McCanny定义的某一种格局来描述某个物种的更新格局。如果群落中所有物种的表现对密度变化的反应都一样,那么优势种受到更强的密度制约,(局域尺度上的)群落的物种(或谱系)多样性将随这群体年龄的增长而增加,死亡后群体的多样性也将增加。本文比较了不同年龄群体的物种和谱系多样性,同时也比较了群体死亡前后物种和谱系多样性的变化。结果表明死亡后物种多样性显著下降,而谱系多样性没有显著变化,说明密度制约并没有在短期内发挥作用。相反,生境过滤可能起着很大的作用。但是结果也表明年长群体比年轻群体在物种和谱系多样性上都高。这虽与密度制约的预期十分一致,但其并非由密度制约效应造成,而更可能是由波动依赖的稳定机制(如储存效应)造成的。但这种稳定机制也仅在山脊等小生境中起作用。综合来看,密度制约对亚热带常绿阔叶林的结构和动态的影响是微弱的,相对于其他因素(如生境异质性、扩散限制、储存效应)密度制约对维持亚热带常绿阔叶林的物种多样性的作用非常有限。更多还原

【Abstract】 Density dependence was considered as an important mechanism to maintain high species diversity in forest. This theory was discussed widely in past40years. There is a long debate among ecologists as to whether density dependence is a community-wide important mechanism in maintenance of species diversity in natural forests. Some empirical and experimental studies supported this theory, but many others not. There are many questions about this theory are waiting for discussion. For example, whether is it prevalent and important in subtropical forest or not? How the effect changes form between species, from stage to stage, and from site to site. In this study, I used the data from5-ha Baishanzu Forest Dynamic Plot (FDP), a part of an evergreen broadleaved forest in the Fengyangshan-Baishanzu National Nature Reserve in eastern China, to investigate the contribution of density dependence to species coexistence in subtropical evergreen broad-leaved forest. The study was divided into three aspects:individual survival analysis, spatial pattern analysis of populations and dynamic analysis of species and phylogenetic diversity.Following density dependence theory, the survival of plants would be impaired by high density (or biomass) of conspecifics or heterspecifics with close phylogenetic relationship. At the same time, herd-protect effects would protect individuals by improving heterospecific density. After controlling effects of self size, habitat heterogeneity and spatial autocorrelation, auto-logistic regression was a good tool to reveal relationship between individual survival and density of conspecifcs/heterospecifics. Results showed that individual survival was strongly influenced by self size; topography somewhat influenced individual survival. Among22analyzed species, only8species exhibited the pattern that individual survival was negatively related to the density (or biomass) of conspecifics. Increase of phylogenetic complexity significantly improved tree survival of2species only, while increase of heterospecific density significantly reduced tree survival of4species. There was no herd-protect effects in the forest. Density dependent effects on trees and seedlings survival did not show significant difference. The effect of density dependence varied among functional guilds, which suggested the strength of this effect depended on species functional traits.If density dependence works in this forest, the clustering should decline and average distance between offspring and adult increase with the age of size classes. In this study, I used point pattern analysis with heterogeneous Poisson process and random labeling to rule out the influence of habitat heterogeneity, and selectively analyze plant-plant interaction. Results showed that spatial distribution of53.3%species we examined did not exhibit any thinning effect of density dependence. For other species that showed thinning effects, the effects were not consistent throughout the whole life history. Few species distributed regularly at adult stage. There were only16.7%species whose non-adults were apart from adults at least at a stage. The distance effect of density dependence did almost not occur in the forest. While63.3%species exhibited the pattern that non-adults were close to adults. Because of coexistence of many processes, the recruitment patterns always change with life stage. Any pattern defined by McCanny can not describe the recruitment pattern of species accurately.If abundant species (or clade) in the community suffer more serious effects of density dependence, species (or phylogenetic) diversity would increase when a group of plants aged. In this study, I compared species and phylogenetic diversity among different size-classes and checked shifts in species and phylogenetic diversity between pre-and post-mortality communities. Results showed that species diversity significantly decreased while phylogenetic diversity kept unchanged after mortality occurring. This suggested that density dependence did not determine species and phylogenetic diversity in short-term, while habitat filtering may work strongly. I also noted that species and phylogenetic diversity increase with ages of size-classes. The finding was consistent with prediction of density dependence, but it was not the result of density dependence, and may be the result of stable processes such as storage effect. However, the stable process was also restricted in ridge.All in all, I believed that the effects of density dependence on structure and dynamics of this subtropical forest were very weak. Relative to other mechanisms, negative density dependence only have little influence on maintenance of species diversity in the subtropical forest.更多还原