【作者】 何兰军；

【导师】 李先琨； 向悟生；

【作者基本信息】 广西师范大学 ， 植物学， 2012， 硕士

【摘要】 种群空间格局分析有利于理解格局形成的原因和物种共存机制。本研究主要从群落学特征、种群结构、空间分布格局动态和种间关联几方面对广西弄岗北热带喀斯特季节性雨林3个典型群落进行了分析。分析结果表明,3个样地内物种组成十分丰富,尤其是单种属非常多,甚至有超过10%的种属于单科单属种。3个样地内所有个体总的径级结构均呈倒“J”型,表明群落稳定且更新、生长良好。对主要建群种径级结构的分析发现,蚬木和肥牛树径级频率分布呈现不连续的状态,这可能是由于在热带喀斯特季节性雨林中,乔木层的中径级个体对光资源的需求增加及种间相互竞争加剧所致；东京桐的胸径主要集中在中径级,小径级和大径级相对较少,更新层缺乏,说明其为远期衰退种。通过空间点格局相关函数g(r)方法分析3个典型群落内主要树种的空间分布格局,发现80%左右的物种几乎在0-20m的尺度上表现为聚集分布。随着研究尺度的增大,随机分布的物种比例有升高趋势,但在不同群落类型中,这种变化趋势并不相同。一般认为,小尺度上的聚集格局主要由扩散限制等种群生物学特性和生境异质性决定,而大尺度上(>20m)的聚集格局主要由生境异质性的影响形成,同时种间的相互作用也会导致聚集格局的形成,因此推测,种子扩散限制等种群生物学特性、种间的相互作用和生境异质性影响可能是3种典型喀斯特季节性雨林种群空间分布格局形成的主要原因。在种群发育过程中,3个群落建群种的空间分布格局随发育过程而变化。蚬木小径级个体在小尺度上形成的“斑块”状分布,在水平空间方向上并不是连续的,而是镶嵌分布于整个群落中。说明蚬木小径级个体的空间分布格局除了受自身更新方式的影响外,可能还与喀斯特石山土壤的不连续性、不均匀性等特性有关。蚬木小径级个体随着DBH的增大,其发生聚集分布的尺度逐渐增大,这可能与植物生长和岩溶作用的密切关系有关。蚬木较大径级个体在较小尺度下表现为随机分布,随着尺度的增加,逐渐过度为聚集分布,后又趋于随机分布。肥牛树从小径级到大径级,发生聚集分布的尺度逐渐缩小,最终随机分布占主导。东京桐各生长阶段个体均以随机分布为主,整个种群也呈随机分布。种群分布格局的变化是种群与生境相互作用的结果,与种群数量的动态变化密切相关,反映了种群的一种适应机制。种群不同生长阶段个体之间的相互关系是种群与环境长期相互作用的结果,也是种群动态与稳定性的标志。对蚬木、肥牛树和东京桐各生长阶段个体间的空间关联性研究,有利于进一步加深对其分布格局形成过程的理解。研究表明,随着径级差距的加大,在小尺度上蚬木小径级个体与较大径级个体之间的空间正相关减弱,而负相关增强；在大尺度上空间关联则呈相反的过程。同时发现种群径级相邻越近,蚬木个体之间在空间分布上基本呈正相关。整体上,蚬木各个生长阶段之间的关系基本上呈正相关,但随尺度变化而发生微弱的变化。肥牛树各生长阶段之间的关联都比较密切,只是存在某些尺度下显著与不显著的差别,但整体上均呈正相关。东京桐各生长阶段个体之间的关系在所有尺度下均为不相关,只是在某些尺度下出现轻微的负相关,而另一些尺度下呈微弱的正相关。一般地,如果在小尺度上小径级个体与成年个体存在正相关,说明扩散限制对格局的形成可能起重要作用。综合上述结果,进一步验证了扩散限制在蚬木种群及肥牛树种群格局形成过程中可能起到非常重要作用,而扩散限制对东京桐种群格局的形成作用不明显。种间空间关联性的研究有助于理解群落内物种之间的相互作用,以及不同物种在不同生境中的定居分异,客观反映物种与环境的关联性。通过对3个典型群落共59个物种对的种间关联分析,结果表明广西弄岗北热带喀斯特地区多对种间关联性不稳定,这可能与弄岗北热带喀斯特石山小生境的不均匀性、不连续性和复杂多样化等特征有关。在某些尺度上由于物种微生态位上的差异,使得物种达到和谐共存,甚至出现伴生现象,而在其他尺度上由于物种对资源利用的相似性,即生态位重叠,资源竞争会导致生态位分化,物种之间在空间上表现为负相关。本区80%左右物种在0-20m的尺度上呈聚集分布,但显著关联种对比例较低。种间个体之间相互作用的机会少,而同种个体紧密聚集,种内相互作用较易发生。这说明扩散限制导致了同种个体聚集分布,而生境异质性促进了种群生态位分化,种群格局发生变化。3个典型群落不同种间空间关联类型累加的结果表明,在所有尺度上,正相关、负相关和不相关所占物种对比例近似,为30%左右。这表明喀斯特季节性雨林物种之间在空间分布上是错综复杂的,物种在空间分布上的分化,促进了喀斯特季节性雨林良性发展。综上所述,3个典型的喀斯特季节性雨林目前处于一种稳定状态。种子扩散限制等种群生物学特性以及生境异质性影响可能是物种空间格局形成的主要机制。由于引起物种空间分布变化的原因是多种多样的,而且不同的生态学过程和机制可以产生相同的格局,如何区分如扩散限制、生境异质性、负密度制约等不同机制的影响以及不同机制对喀斯特季节性雨林生物多样性维持的贡献,还需要进一步深入研究。更多还原

【Abstract】 Spatial patterns analysis of plants may provide significant insights into processes and mechanisms of species coexistence in forest communities. In order to understand community dynamics and mechanisms that control the distribution of species in tropical karst seasonal rainforests in Guangxi Nonggang Nature Reserve, we analyzed community characteristics, population structure, spatial pattern dynamics and spatial associations of dominant plant species of three1-ha tropical karst seasonal forest communities.We found that the three communities were species rich. The communities also had high taxonomic diversity with more than10%of species belonging to single genera and single family. The structure of DBH size class of all species in each of the three plots generally showed inverse "J" shape, indicating that all of the three communities were stable and successful regeneration. The frequency distributions of DBH size class of Excentrodendron hsienmu and Cephalomappa sinensis, the two constructive species, were discrete, which may be due to the middle layer species were easy damaged in a tropical karst seasonal rainforest. By comparison, the structure of DBH size class of Deutzianthus tonkinensis, another constructive species, was unimodal, which indicated that it would become a declining species in the future.By using the spatial point pattern correlation function g (r), we analyzed spatial distributions of dominant species in the three typical communities. The results showed that the distribution patters about80%of species were aggregative at scales of0-20m, and the percentage of species exhibiting a random or regular pattern increased with scale, mainly occurring at scales of>20m. Biological characteristics (e.g. seed dispersal limitation), and environmental heterogeneity may be the important factor to shape the species spatial distribution in this area.The spatial patterns of three constructive species changed with development of the communities. The patches distribution of Excentrodendron hsienmu at small scale was not continuous in horizontal direction and showing a mosaic distribution across the community, which indicated Excentrodendron hsienmu spatial patterns was not only influenced by their own regeneration type, but related to the heterogeneous distribution of karst rocky mountain soil. The scale of clustered distribution increased as the DBH size of Excentrodendron hsienmu grew. Larger DBH size class individuals of Excentrodendron hsienmu showed random distribution, and it gradually became aggregated distribution as the scale increased and finally tended to be random distribution. Form small to large diameter of Cephalomappa sinensis individuals, the scale of aggregate distribution is gradually reduced, and eventually showed random distribut. Deutzianthus tonkinensis were mainly randomly distributed at different growth stages. The variation of population distribution pattern resulted from the interaction between populations and environment, which reflected an adaptation mechanism of the population.The relationship between different age classes of individuals was a result of long-term interactions between populations and the environment, and hence it could provide an insight into population dynamics and stability. The spatial associations of different growth stages of Excentrodendron hsienmu, Cephalomappa sinensis and Deutzianthus tonkinensis could facilitate can distinguish our understanding of the mechanism that produced their spatial patterns. The results showed that positive interactions were to be found between small individuals and larger individuals of Excentrodendron hsienmu at small scale. On the whole, the relationships between the different growth stages of Excentrodendron hsienmu were basically positive interactions, and only slightly changed with the scale. Positive interactions were found between the different growth stages of Cephalomappa sinensis except at several certain scales. No significant spatial associations between the different growth stages of Deutzianthus tonkinensis were observed at all spatial scales. Therefore, to sum up, the results verified that dispersal limitation may play an important role in determining spatial patterns of Excentrodendron hsienmu and Cephalomappa sinensis.Exploring interspecific spatial associations are helpful in understanding the interactions between species within the community and the niche differentiation among species. We analyzed59species pairs, and the results showed that interspecific associations of some species pairs were unstable. Because of the high habitat heterogeneity, resources competition between species-pairs at one scale could lead to niche differentiation; at the other scales, species-pairs could coexist and even became companions. This area about80%of species-pairs showed aggregated distribution at scale of0-20m, but few species-pairs displayed significant associations. These results suggested that dispersal limitation may cause the interspecific individuals aggregated distribution, in contrast, habitat heterogeneity resulted in the population niche differentiation.We found that the proportions of positive interactions, negative interactions and spatial segregation were about30%, respectively, indicating that the spatial distribution were complex, and spatial segregation promoted successful regeneration in the karst seasonal rainforest.In summary, the three typical karst seasonal rainforest communities were now in stable status. Biological characteristics (e.g. seed dispersal limitation), and environmental heterogeneity may be the important mechanism to shape species spatial pattern in this area. However, different ecological processes and mechanisms can produce the same distribution pattern, how to distinguish the different mechanisms such as dispersal limitation, habitat heterogeneity and negative density dependence which contribute to maintain the biodiversity in the karst seasonal rainforeststill remains to be explored.更多还原