物种多度和径级尺度对于评价群落系统发育结构的影响:以尖峰岭热带山地雨林为例

Effects of species abundance and size classes on assessing community phylogenetic structure: a case study in Jianfengling tropical montane rainforest

研究不同径级尺度群落系统发育多样性有助于了解不同年龄模式下物种的亲缘关系及其群落系统发育结构;但是关于物种多度对群落系统发育结构影响的研究较少。以海南尖峰岭热带山地雨林群落为例,首先在不同径级尺度比较物种多度加权与否分别对4个广泛采用的系统发育指数的影响,继而利用其中2个经过标准化处理的系统发育多样性指数:净种间亲缘关系指数(net relatedness index,NRI)和净最近种间亲缘关系指数(nearest taxon index,NTI),结合群落的生境类型来量度不同局域生境条件下不同径级尺度木本植物系统发育关系。结果发现:(1)未考虑物种多度加权的系统发育平均成对距离(mean pairwise distance,MPD)指数比考虑物种多度加权的MPD指数显著地高估了群落整体系统发育多样性,且这种现象在小径级尺度(1 cm≤DBH<5 cm)最为明显。因此,在森林监测样地中对于中、小径级群落系统发育结构研究中建议考虑物种多度信息。(2)从群落组成整体系统发育结构来看,尖峰岭热带山地雨林在几乎所有径级尺度和生境下均倾向于系统发育发散,且随着径级的递增发散程度趋于明显(NRI<0)。(3)从群落组成局部系统发育结构来看,尖峰岭热带山地雨林在中、小径级倾向于系统发育聚集(NTI>0),而在大径级(DBH≥15 cm)则倾向于系统发育发散(NTI<0)。总之,研究群落系统发育结构时应考虑物种多度的影响以及径级尺度效应。

Studying community phylogenetic diversity within forest stands of different diameter classes（i.e. size classes） is helpful for understanding relationships among species at different ages while at the same time community phylogenetic structure. However, little research has been focused on the influence of species abundance on phylogenetic structure of community. This study was conducted in the Jianfengling tropical montane rainforest on Hainan Island. First, we assessed the impact of species abundance on four widely used phylogenetic diversity indices at different size classes. Next, two of the indices（i.e. net relatedness index,NRI and nearest taxon index, NTI） were standardized and used to quantify phylogenetic relatedness of woody plants at different size classes across a series of local habitat types. The results showed that：（1） The unweighted MPD（mean pairwise distance） index significantly overestimated phylogenetic diversity relative to MPD weighted according to species abundance. This overestimation when using unweighted MPD was greatest for small trees and shrubs（1 cm≤DBH〈5 cm）. Therefore species abundance information should be taken into consideration in the study of phylogenetic structure of community when most of the trees and shrubs are young and small.（2） The community phylogenetic structure was most likely overdispersed among almost all size classes and habitats of the Jianfengling tropical montane rainforest（NRI〈0）. This phylogenetic overdispersion increased as size class increased.（3） The partial community phylogenetic structure tended to be clustered at middle and small size classes（NTI〉0）. However, this pattern continued to show overdispersion within communities made up of large trees（DBH≥15 cm）（NTI〈0）. In summary, studies assessing the influences of species abundance and size classes on community phylogenetic structure are required.