【作者】 方晓峰；

【导师】 王希华；

【作者基本信息】 华东师范大学 ， 生态学， 2016， 博士

【摘要】 作为亚热带地区的地带性植被,常绿阔叶林中孕育着十分丰富的生物资源,是该区域生物多样性的宝库。在这一生态系统中业已开展了不少有关生物多样性格局及物种共存方面的研究,而且这些研究常常涉及到物种、谱系进化以及功能性状等多个层次。但是,在生活型水平上,特别是针对常绿阔叶林中普遍共存的两类生活型:常绿与落叶物种而言,所进行的类似研究却较为鲜见。常绿与落叶树种是两类有着不同物候特性与生长策略的物种的集合,因此分析两者在常绿阔叶林中的物种多样性特征,探讨它们在样地内的共存机制,既能够为理解常绿阔叶林内物种多样性的形成与维持机制提供一个全新的视角,也将有助于从生活型水平上预测全球变化背景下的群落响应;同时,亦可为受损常绿阔叶林生态系统的恢复与重建工作提供必要的理论与数据支撑。基于2010年的调查结果,天童20 ha常绿阔叶林动态监测样地内共生长有152种胸径≥1 cm的木本植物,这当中的73种为常绿树种,其余的79种为落叶树种。虽然在物种丰富度方面不及落叶树种,但常绿物种却在物种多度和胸高断面积等指标上占有绝对优势。本研究以该常绿阔叶林样地内的常绿与落叶树种为研究对象,意在回答两个问题:(1)在天童常绿阔叶林中,常绿与落叶树种各自的多样性格局有哪些特征?(2)常绿与落叶树种在天童样地内是如何实现共存的?为此,本文一方面从物种多度分布以及β多样性特征的角度对比了两类生活型物种在其多样性格局上的异同,探讨了这些差异背后的可能成因;另一方面,分析了不同空间尺度下以及不同个体发育阶段间,驱动二者在常绿阔叶林中长期共存的生态学过程。初步归纳出下述的主要结果与结论:(1)采用累积经验分布函数对常绿与落叶植物的物种多度分布进行描述,经Kolmogorov-Smirnov检验(K-S检验)后证明二者在物种多度分布上并无显著差异。利用纯统计模型、生态位模型和中性理论模型对两类生活型的物种多度分布进行了拟合,根据K-S检验及AIC值两项标准进行评判后发现,中性理论模型的拟合效果是最好的,而生态位模型的拟合效果则较为一般。从上述结果中可以看出,尽管常绿与落叶树种在物种数量和多度方面都存在差异,但它们却有着近似的物种多度分布格局。但是,鉴于模型拟合的结果只能作为理解群落多样性构建机制的必要非充分条件,故而只能初步判定中性过程对于常绿与落叶植物两者的物种多样性格局影响更大,却并不能排除或衡量诸如生态位分化等其他过程在两类生活型多样性格局形成中的贡献。(2)对天童样地内常绿与落叶植物各自的β多样性进行了计算,并将其进一步分解为物种替换和丰富度/多度差异两部分,继而结合环境变量(地形因子和土壤因子)以及空间结构变量(PCNM),使用基于距离矩阵的冗余分析(db-RDA)计算出两类变量对于常绿与落叶树种β多样性及其各组分的贡献率,以确定生态位过程和扩散过程在两类物种β多样性格局形成过程中的相对重要性。结果显示,相对于常绿树种而言,落叶树种有着更高的β多样性。物种替代过程对于两类生活型物种β多样性的决定作用均高于丰富度/多度差异过程,说明样地中不同样方间常绿或落叶植物种类组成上的差异是各生活型β多样性的主要来源。同时,生态位过程与扩散过程共同影响着两类物种β多样性格局的形成,但后者的贡献率更高,这与结论(1)中的判断相吻合,即相较于生态位过程,中性过程对常绿与落叶树种多样性格局的形成更为重要。而且,鉴于生态位过程以及扩散过程对于落叶树种β多样性的总解释度较低,可以认为某些纯随机的过程(如林窗的形成)在落叶树种β多样性格局形成中的影响可能更大。(3)为了探讨天童样地内常绿与落叶树种在不同空间尺度下的共存,利用空间点格局分析的方法对它们各自的空间分布格局以及二者间的空间关联进行了研究。使用异质性泊松零模型剔除生境异质性对于个体密度的影响,以判断生境过滤过程在两类生活型物种共存中的作用;最后使用多元回归树方法对10 m、20 m和50 m尺度下常绿与落叶树种的生境偏好进行了分析和检验。结果显示,常绿与落叶树种分别在小于125 m和60 m的尺度上表现出显著的空间聚集,此外两者在小于120 m的尺度下表现为空间上的互斥,但当生境异质性的影响被去除后这种空间分离的情况就消失了。在前述的三个空间尺度下(10m、20m和50 m),两类物种对于土壤全磷含量表现出了相反的偏好,例如落叶物种往往在土壤全磷含量较高(0.27-0.30 g·kg-1)的生境中占有优势。以上结果表明天童样地内常绿与落叶树种的镶嵌分布格局主要是由生境过滤过程所导致的,而且微生境异质性在其中也起到了非常重要的作用。此外,土壤全磷含量可能是维持两者共存格局的主要环境因子。(4)通过将样地内的常绿与落叶物种依据其胸径划分为幼树、中树和成树三个阶段,探讨了不同个体发育阶段间两类物种的共存。利用空间点格局分析及空间自相关回归的手段,分析了两类生活型在不同发育阶段内的空间格局、空间关联性以及生境偏好的变化情况。结果表明,处于不同发育阶段中的常绿与落叶树种间,在较小尺度下主要表现为空间分离,且随着植物个体从幼树发育到成树阶段,其分离的空间尺度也往往有增大的趋势,但这种排斥在使用异质性泊松零模型将环境异质性的影响去除后便消失了。空间自相关回归的结果表明,随着个体发育阶段的改变,常绿或落叶物种自身对于生境的选择会发生改变,但二者之间依旧表现出对某些环境因子的不同偏好。结合两方面的分析结果可知,即使是处在不同发育阶段的常绿与落叶树种,生境过滤依然是影响它们共存的重要过程。综合以上结果,在天童常绿阔叶林中,常绿与落叶树种有着相似的物种多样性形成机制,它们的多样性格局均受到生态位过程和中性过程的综合作用,但是以扩散过程为代表的中性过程影响更大。至于常绿与落叶树种在样地内的共存,即使研究的空间尺度不同,个体所处的发育阶段迥异,生境过滤可能依然是其共存格局背后重要的生态学过程。更多还原

【Abstract】 As the zone vegetation in the subtropical area,evergreen broad-leaved forest(EBLF)is rich in species diversity and includes several global biodiversity hotspots.Researches about the bidoversity pattern and species coexistence in the EBLF are prevalent.Ecologists have studied the topic in different aspects,such as species,phylogeny and plant functional traits.However,they rarely conduct the relevant reserach at the life form level,especially for the evergreen and deciduous tree species,which are the two major life form compositions in EBLFs.Evergreen and deciduous plants are two types of species with distinct phenological characteristics and growth strategies.It is valuable for analyzing their species diversity characteristics separately,and detecting the mecahnisms of their coexistence in EBLFs.Specifically,the study may provide a new angle on the understanding of generation and maintenance of speices diversity in EBLFs;it is helpful in predicting the community responses to the global change based on the life form;such work will provide some necesary theoretical and experimental data underpinning the practice of biodiversity protection and restoration as well.According to the result of investigation in the autumn of 2010,152 woody plants whose diameters at breast height(DBH)≥ 1 cm were recorded in the 20 ha stem-mapped EBLF dynamic plot in Tiantong National Forest Park,consisted of 79 deciduous and 73 evergreen tree species.Compared to deciduous plants,evergreen species were slightly lower in species richness but substantially higher in abundance and basal area.In this study,we focus on the evergreen and deciduous tree species in the EBLF plots and attempt to answer the following two questions:(1)what are the characteristcs of diversity patterns of evergreen and deciduous trees in Tiantong EBLF?(2)How do these two life forms coexist in the Tiantong plot?Therefore,the species abundance distributions and β diversity patterns of each life form were compared and the potential reasons were discussed.Besides,we also tried to recognize the ecological processes influencing the coexistence of these two life forms in various spatial scales and different ontogentic stages.The main results and conclusions of this study are listed as follows:(1)Empirical cumulative distribution function(ECDF)was utilized to describe the species abundance distribution(SAD)of evergreen and deciduous species,whereas the differences of SAD between the two life forms were not significant according to the result of Kolmogorov-Smirnov test(K-S test).Three types of models,ie.,statistic model(log-normal model and log-series model),niche model(broken-stick model and niche preemption model)and neutral theory model(metacommunity zero-sum multinomial distribution model and Volkov model),were used to fit the SAD of each life form.With reference to the results of K-S test and AIC values,the best fitting model was the neutral theory model,and the niche model showed the poorest fitting of the data.Thus we could conclude that evergreen and deciduous trees had similar SAD pattern,although they are different in species richness and abundance.However,the model fitting results were commonly deermed as the necessary but insufficient condition in understanding the forming mechanism of biodiversity.Hence we could only preliminarily conclude that neutral process had a major effect on the generation of biodiversity pattern of either evergreen and deciduous plants,whereas the possible contributions made by other processes,such as niche differentiations,could not be excluded and measured by this method merely.(2)We calculated the beta-diversity index of evergreen and deciduous plants in Tiantong plot,and further partitioned it into two parts:species replacement and richness/abundance difference.The environmental variables(topographic factors and edaphic factors)and spatial structure variables(PCNM)were employed in the distance-based redundancy analysis(db-RDA)calculating the contribution rates of each variable on the beta-diversity index and the two beta-diversity components for each life form,in order to determine the relative importantce of niche and dispersal.The beta-diversity of deciduous plants was higher than that of evergreen species.Species replacement process was more important than richness/abundance difference process in determining the beta-diversity of both life forms indicating the discrepancy in species of either evergreen or deciduous plants among quadrats were the main source of their beta-diversity.Dispersal process had more effect on the beta-diversity pattern of evergreen and deciduous plants,although niche differentiation and neutral dispersal process influenced such pattern simultaneously.This is in line with the result(1),which stressed the significance of neutral process in shaping the diversity patterns of evergreen and deciduous trees.Moreover,by virtue of the low overall interpretation degree of variation of beta-diversity of deciduous plants by both niche and dispersal processes,pure random processes such as the present of forest gaps might be more important in generating the diversity pattern of deciduous plants.(3)Mosaics of evergreen and deciduous trees that are characteristic of EBLF are thought to arise from habitat filtering,but empirical evidence for this is limited.We test this assertion asking(i)whether environmental heterogeneity explains the distribution of deciduous and evergreen trees;(ii)which are the most important environmental variables;and,(iii)does their importance change with scale?We used data from a 20-ha individual-mapped EBLF in spatial point pattern analyses testing the scale of aggregation within,and segregation between,the two life forms.We used a heterogeneous Poisson process model to remove the effects of environmental heterogeneity,predicting segregation would disappear if the mosaics were due to habitat filtering alone.Finally we tested the relative importance of theoretically important environmental variables using multivariate regression trees at three spatial scales(10,20 and 50 m grid cells).We found evergreen and deciduous trees were aggregated at scales below 125 m and 60 m respectively and mutually exclusive at scales<120 m.Evidence of any spatial segregation between the life forms was removed at all scales after controlling for environmental heterogeneity.Only soil phosphorous concentrations contributed to spatial patterns at all scales,with values greater than 0.27-0.30 g·kg-1 favouring deciduous species.Our study is consistent with habitat filtering creating the observed mosaics of evergreen and deciduous tree species,but micro-habitat heterogeneity contributed even at scales below 20 m.Soil phosphorus availability appears to be the major environmental variable maintaining these mosaic patterns at hillslope scales in EBLF.(4)In order to deliberate on the ecological processes influencing the coexistence of evergreen and deciduous tree speices in different ontogenetic stages,we divided each of the two life forms into three ontogenetic stages(sapling,juvenile and mature)in the light of their DBH.We analyzed the spatial association and habitat preference within and between each ontogenetic stage of the two life forms using spatial point pattern analysis and spatial autocorrelation regression(SAR)analysis.We found that these two life forms in distinct life stages presented a spatial repulsion at relative small scales,and with the developing of individuals of evergreen and deciduous plants the segregated spatial scales increased.Whereas the segregation situation disappeared while the habitat heterogeneities were removed by heterogeneous Poisson process model.The SAR result denoted that albeit the preference of either evergreen or deciduous plants would transform along with the growth of their individuals,the two life forms still performed divergent preference in certain environmental elements.Combinng with these findings,habitat filtering was still the main process mediating the coexistence of the two life forms even for evergreen and deciduous individuals in distinct ontogenetic stages.In summary,evergreen and deciduous trees in Tiantong EBLF possessed similar mechanism in determining their diversity patterns:their species diversity patterns were influenced by both niche and neutral process,whereas the neutral process represented by dispersal process was more important.As to the coexistence of the two life forms,habitat filtering could be the main promoting force behind the pattern,in spite of the differences in spatial scales and ontogenetic stages.更多还原