Patterns and processes in complex landscapes: testing alternative biogeographic hypotheses through integrated analysis of phylogeography and community ecology in Hawai'i

The Island of Hawai‘i is a dynamic assemblage of five volcanoes with wet forest habitat currently existing in four distinct natural regions that vary in area, age, and geographic isolation. In this complex landscape, alternative assumptions of the relative importance of specific habitat characteristics on evolutionary and ecological processes predict strikingly different general patterns of local diversity and regional similarity. In this study we compare alternative a priori hypotheses against observed patterns within two distinct biological systems and scales: community composition of wet forest vascular plant species and mitochondrial and nuclear genes of Drosophila sproati, a wet forest restricted endemic. All observed patterns display strong and similar regional structuring, with the greatest local diversity found in Kohala and the windward side of Mauna Loa, the least in Ka‘ū and Kona, and a distinctive pattern of regional similarity that likely reflects the historical development of this habitat on the island. These observations largely corroborate a biogeographic model that integrates multiple lines of evidence, including climatic reconstruction, over those relying on single measures, such as current habitat configuration or substrate age. This method of testing alternative hypotheses across biological systems and scales is an innovative approach for understanding complex landscapes and should prove valuable in diverse biogeographic systems.

夏威夷岛（Island of Hawai‘i）是由五座火山构成的动态综合体，当前其境内留存有四块面积、形成年代与地理隔离程度均存在差异的独立天然区域，各区域均分布有湿润森林生境。在这一复杂的地貌系统中，针对特定生境特征在演化与生态过程中的相对重要性所提出的多种不同假设，会推导出截然不同的局域多样性与区域相似性总体格局。本研究针对两类不同生物系统与研究尺度下的观测格局，对多种先验备选假设进行对比检验：其一为湿润森林维管植物物种的群落组成，其二为专性栖息于湿润森林的特有种——斯普罗蒂果蝇（Drosophila sproati）的线粒体与核基因序列。所有观测格局均呈现出显著且一致的区域结构特征：局域多样性最高的区域为科哈拉山与冒纳罗亚火山的迎风坡，最低的区域为卡乌与科纳地区；同时存在一类独特的区域相似性格局，该格局大概率反映了该岛湿润森林生境的历史演化进程。上述观测结果在很大程度上支持了整合多维度证据（包括气候重建结果）的生物地理学模型，而非仅依赖单一指标（如当前生境配置或基底形成年代）的模型。这种跨生物系统与研究尺度检验备选假设的研究方法，是解析复杂地貌系统的创新性路径，有望在各类生物地理学研究中展现重要应用价值。