小岛屿效应描述了种-面积关系的一种特殊现象, 是当前生物地理学和生物多样性研究理论框架的重要组成部分。随着气候变暖, 山顶物种的生存受到威胁, 然而以山顶生境岛屿为载体对小岛屿效应的研究还十分缺乏。该研究以太行山脉中段19个面积0.06-801.58 km²的山顶生境岛屿为研究区, 在2019-2021年的夏秋季对藓类进行调查。共记录到藓类131种, 隶属于23科68属。采用6种种-面积关系回归模型, 分别检测了所有藓和6个常见藓科是否存在小岛屿效应。根据小岛屿效应形成机制的生境多样性假说、灭亡假说和营养补给假说, 选择了岛屿高度、温度年变化范围和单位面积净初级生产力作为变量, 对小岛屿效应的驱动因素进行分析。在各类群组中, 使用多元线性回归和变差分解分别评估上述3个变量对物种丰富度变化的线性影响。首先使用5个面积最小的岛屿进行分析, 计算出3个变量对物种丰富度变化的贡献, 然后以迭代的方式逐次加入面积更大的1个岛屿, 并再次进行变差分解分析。最后使用广义线性回归分析了3个变量对物种丰富度变化的贡献在迭代过程中的变化趋势。结果显示, 所有藓和6个常见藓科均存在小岛屿效应, 其面积阈值分布在0.36-106.91 km²间。各组藓类小岛屿效应的驱动因素具有差异性, 其中, 除了紫萼藓科之外, 其他各组均支持生境假说; 除了丛藓科、真藓科、紫萼藓科和灰藓科之外, 其他各组均支持灭亡假说; 而各组在不同程度上普遍支持营养补给假说。整体而言, 面积约为10 km²以上的岛屿维持了大量的藓类物种多样性, 需要重点保护。对于生境要求较为单一的紫萼藓科而言, 保护石生环境是保护其物种多样性的关键; 而对于其他科藓类而言, 生境类型多样性的保护是维持物种多样性的重要保障。营养补给假说的普遍适用性揭示了山顶下方森林生态系统的资源补给作用减缓了由于面积的减小而造成的藓类物种数量下降, 因此保护山顶下方林地内物种多样性和群落稳定性对维持山顶藓类物种多样性具有重要意义。

Aims As an anomalous feature of the species-area relationship (SAR), the small-island effect (SIE) is an important pattern in the fields of island biogeography and biodiversity science. However, the existing work has rarely explored the SIE in fragmented mountaintops. Moreover, the underlying factors determining the SIE remain largely untested. In this paper, we aimed to evaluate the prevalence and underlying factors determining the occurrence of SIEs in mosses on mountaintops of the Middle Taihang Mountains.
Methods We investigated and compiled data on the species richness of all mosses and six most common moss families on 19 mountaintops of the Middle Taihang Mountains. For each of the seven taxonomic groups, we applied six SAR models, including four piecewise regressions with two segments, a linear regression, and a zero-slope regression as a null model, to detect the SIE and then used the corrected Akaike’s information criterion (AICc) as a criterion to select the best model. We obtained three environmental variables, including island height, annual temperature range, and net primary productivity per unit area that are linked to the habitat diversity hypothesis, the extinction hypothesis, and the subsidized island biogeography hypothesis, respectively, in order to explore the underlying drivers of the SIE. We applied iterative multiple linear regression and variation partitioning to determine the effects of island area and each of environmental variables on species richness for islands of varying sizes. Finally, we analyzed the trends of environmental variables’ contributions to species richness variation over the iterative process by using generalized linear regressions with polynomials of area up to the second degree.
Important findings A total of 131 moss species, belonging to 23 genera under 68 families, were identified. SIEs were detected for all mosses and six most common moss families, with the area thresholds varing between 0.36 km² and 106.91 km². The driving factors of the SIE differentiate among groups. Among them, Grimmiaceae did not support the habitat diversity hypothesis; Pottiaceae, Bryaceae, Grimmiaceae, and Hypnaceae did not support the extinction hypothesis; whereas, the subsidized island biogeography hypothesis was generally supported by each group to varying degrees. On the whole, mountaintops with an area of ​​over 10 km² maintain a large diversity of moss species and thus be identified as site conservation targets. For mosses with relatively unique habitat requirement, such as Grimmiaceae, protecting the stony habitat is the key to maintain its species diversity; as for other mosses, conservation of habitat diversity is the key to maintain their species diversity. The general applicability of the subsidized island biogeography hypothesis suggests that the resource replenishment of the forest ecosystem below the mountaintops counteracts the removal of mosses’ species richness due to area reduction. Therefore, conservation of species diversity and community stability in the forest below the mountaintops is essential for sustaining moss species diversity in fragmented mountaintops.