Isolation drives species gains and losses of insect metacommunities over time in a mountaintop forest archipelago

Aim: We evaluated the effects of forest island size, isolation, and area in the landscape driving temporal changes of insect biodiversity in a mountaintop forest archipelago. We tested the following hypotheses: (i) changes in insect species composition is higher and dominated by species gains through time in smaller but less isolated forest islands; (ii) larger amounts of forest in the landscape result in higher gains of more vagile species over time, regardless of their size and isolation; (iii) heterogenization processes will prevail in less vagile groups, while homogenization processes will dominate in highly vagile groups due to differences in dispersal capability. Location: Espinhaço Range Biosphere Reserve, Brazil. Taxon: Insects. Methods: We used ants, dung beetles, bees, wasps, and butterflies as study models to represent a gradient of low-to-high dispersal capability. We evaluated the colonization- and extirpation-resultant components of temporal β-diversity using area- and isolation-related variables as predictors. Results: We found distinct colonization- and extirpation-resultant homogenization and heterogenization processes acting according to each insect group, likely due to different dispersal capabilities. Ants were dominated by species losses, with widespread and rare species being lost. Butterflies gained species, represented mainly by widespread species, leading to an increased colonization-resultant homogenization. Distance to neighboring forest islands was the underlying predictor affecting the temporal β-diversity of insect groups and on species gains and losses but differed according to the survey period. Effects of the forest amount in the landscape increased the temporal β-diversity of bees and butterflies but decreased that of ants, dung beetles, and wasps. Main Conclusions: We recommend conserving the forest amount in the landscape and keeping forest connectivity among forest islands since the temporal dynamics of local colonization and extirpation can depend on the organisms' dispersal capability. Fragmentation and habitat loss-related hypotheses will benefit from incorporating colonization-extirpation processes into their predictions.

研究目的：本研究旨在评估山顶森林群岛（mountaintop forest archipelago）景观中，森林岛（forest island）的面积、隔离程度及景观内森林总面积对昆虫生物多样性时间动态的驱动效应。我们验证了以下三项假说：（1）相较于面积更大、隔离度更高的森林岛，面积更小且隔离度更低的森林岛的昆虫物种组成变化幅度更为显著，且随时间推移以物种定殖占主导；（2）无论森林岛自身的面积与隔离程度如何，景观内森林总面积越高，随时间推移移动性（vagile）更强的物种定殖量越多；（3）由于扩散能力存在差异，扩散能力较弱的昆虫类群将以群落异质化（heterogenization）过程为主导，而扩散能力较强的类群则以群落均质化（homogenization）过程占优。
研究区域：巴西埃斯皮尼亚苏山脉生物圈保护区（Espinhaço Range Biosphere Reserve）。
研究类群：昆虫。
研究方法：本研究选取蚂蚁、粪金龟、蜜蜂、胡蜂及蝴蝶作为研究模型，用以代表从低到高的扩散能力梯度。我们以与森林岛面积、隔离程度相关的变量作为预测因子，分析了时间尺度β多样性（β-diversity）中由定殖与局域灭绝（extirpation）共同塑造的组成分量。
研究结果：我们发现不同昆虫类群存在差异化的、由定殖与局域灭绝共同介导的群落均质化与异质化过程，这一差异大概率源于类群间扩散能力的不同。蚂蚁类群以物种局域灭绝为主，丧失的物种涵盖广布种与稀有种；蝴蝶类群则以物种定殖为主，新增物种以广布种为主，进而导致由定殖介导的群落均质化程度提升。与邻近森林岛的空间距离是影响昆虫类群时间尺度β多样性及物种增减的核心预测因子，但其效应随调查时期发生变化。景观内森林总面积提升会增加蜜蜂与蝴蝶的时间尺度β多样性，但会降低蚂蚁、粪金龟与胡蜂的时间尺度β多样性。
主要结论：本研究建议保护景观内的森林总面积，并维持森林岛之间的森林连通性，因为局域定殖与局域灭绝的时间动态取决于生物的扩散能力。将定殖-局域灭绝过程纳入预测框架，将有助于完善与生境破碎化及栖息地丧失相关的生态学假说。