温州沿海小型海岛植物丰富度和β多样性及其影响因子

Factors affecting species richness and beta diversity of vascular plants on small islands in the Wenzhou region of eastern China

于2012-2015年调查了温州沿海20个小型无居民海岛的植物组成,共记录到维管束植物366种,隶属于95科244属,其中草本植物226种木本植物140种。拟合了5个种-面积关系模型,采用赤池信息量AIC对模型进行选择,发现种-面积-生境类型关系模型SAH_nR权重系数最大,为40.26%,两种断点回归种-面积关系模型BR-SAR权重系数分别仅为6.94%和0.43%,表明基于这20个海岛拟合的种-面积关系不存在小岛屿效应。岛屿植物物种丰富度主要受面积A影响,离大陆距离,I_m对丰富度无显著作用;偏相关分析表明除A外,周长/面积比PAR和岛屿生境多样性指数H_d显著影响了植物丰富度,其逐步回归方程分别为:植物总丰富度S=76.714+1.696A-0.046PAR,R^2=0.839;木本植物丰富度S_(-woody)=6.525+0.455A+24.544H_d,R^2=0.697;草本植物丰富度S_(-herbaceous)=66.899+1.285A-0.04PAR-23.434H_d,R^2=0.865。偏最小二乘回归PLS分析中岛屿空间特征参数对岛屿物种相似性指数重要性排序为:I_m(0.61)>I_i(0.56)>PAR(0.49)>A(0.20)>岸线长度Per(0.14)>生境类型H(0.072)>岛屿高程E(0.065)>岛屿形状指数SI(0.05)。由此可见,近岸的小型海岛植物丰富度并不总是由岛屿面积来决定;隔离度对岛屿植物β多样性影响较大。

We conducted field surveys on 20 small, uninhabited islands off the coast of Wenzhou in the Pacific Ocean and recorded 366 vascular plants belonging to 244 genera and 96 families. Of these, 140 were woody and 226 were herbaceous species. Five regression models were constructed to predict species richness （S） and β diversity and the final models were selected based on the Akaike information criterion （AIC）. The effects of island size （A）, distance to the mainland （Im）, inter-island distance （Ii）, shoreline length （Per）, perimeter to area ratio （PAR）, elevation （E）, habitat types （Hn）, habitat diversity （Hd）, and island shape index （SI） were examined. Model SAHnR had the highest Akaike weight, 40.26%, with a ratio of 1.19, 2.17, 5.80, and 94.08 over SAR, SAHdR, BR-SAR1, and BR-SAR2, respectively. Species richness increased with island size following the classic species-area relationship. However, the species similarity index decreased with increasing Ii. The importance of all exploratory variables on β diversity was Im =0.61, Ii =0.56, PAR=0.49, A= 0.20, Per =0.14, Hn =0.072, E =0.065, and SI=0.05, suggesting that isolation （i.e., Im and Ii） played a major role in β diversity. Plant species richness was also significantly affected by PAR and Hd. Stepwise regression showed that the best models to predict S were：S =76.714＋1.696A-0.046PAR （R^2=0.839）, S_woody=6.525＋0.455A＋24.544Hd （R^2=0.697）, and S_herb aceous=66.899＋1.285A-0.04PAR-23.434Hd （R^2=0.865） for total, woody, and herbaceous species richness, respectively. This further indicated that species richness of different growth forms （i.e., woody and herbaceous） on these islands was not solely dependent on island size.