Terrestrial invertebrates surviving San Ambrosio island’s ecological catastrophe reinforce biogeographic affinities between the Juan Fernández and Desventuradas Islands

Islands are hotspots of biodiversity and extinction. It is critical to study their unique island life before it is lost forever. The Desventuradas Islands, comprised of San Félix and San Ambrosio islands, are a volcanic archipelago 850 km off the coast of Chile. They are key to understanding the diversification processes which shaped the flora and fauna of other Chilean oceanic islands such as the Juan Fernández Archipelago. But, the biogeographic affinities between these archipelagos are still poorly known. Over the last century, the plant and animal communities present in the Desventuradas have radically changed due to invasive mammal introductions. Here, focusing on terrestrial invertebrates, we: (1) confirm the presence of described endemic species, (2) detect new species records and (3) assess the biogeographic affinities between the Juan Fernández and Desventuradas archipelagos. In September 2018, San Ambrosio was surveyed using different methods (hand collecting, beating sheet, entomological net, pitfall traps and light traps) at night and during the day. A total of 35 morphospecies were collected. Four endemic species were found, in addition to several previously described higher taxonomic groups with undescribed species. Collecting methods were not successful in detecting another nine previously described endemic species. There was a total of 28 new records, including a new land snail, a new Isopoda and representatives of five spider families. Twelve of all the recorded genera from Desventuradas Islands have known relatives in the Juan Fernández Archipelago. Five of them were not previously known for San Ambrosio, reinforcing the biogeographic affinities between both archipelagos. This research highlights the urgency of surveying islands subject to a multitude of threats, including climate change and invasive species, to generate baseline data and place the island’s fauna in a broader biogeographical context.

岛屿是生物多样性与物种灭绝的热点区域。在独特的岛屿生物永久消失前，对其开展研究至关重要。德森塔杜拉斯群岛（Desventuradas Islands）由圣费利克斯岛（San Félix）与圣安布罗西奥岛（San Ambrosio）组成，是距智利海岸850公里的火山群岛。该群岛是理解塑造智利其他洋岛（如胡安·费尔南德斯群岛（Juan Fernández Archipelago））动植物区系的物种分化过程的关键所在。但目前学界对这两类群岛之间的生物地理亲缘关系仍知之甚少。
过去一个世纪以来，德森塔杜拉斯群岛的动植物群落因外来哺乳动物的引入发生了剧烈变化。本研究聚焦陆生无脊椎动物，完成了三项核心工作：（1）确认已描述特有物种的存在；（2）发现新物种记录；（3）评估胡安·费尔南德斯群岛与德森塔杜拉斯群岛间的生物地理亲缘关系。
2018年9月，研究团队采用多种调查方法（手采、振落采样拍盘、昆虫网、陷捕器以及灯光诱捕器），在圣安布罗西奥岛开展了昼夜调查。本次调查共采集到35个形态种。除发现数个携带有未描述物种的已描述高级分类群外，还记录到4个特有物种。但部分采样方法未能检出另外9种此前已被描述的特有物种。
本次调查共计获得28个新记录，包括1个新陆生蜗牛类群、1个新等足目（Isopoda）物种以及5个蜘蛛科的代表类群。德森塔杜拉斯群岛记录到的12个属，其已知近缘类群分布于胡安·费尔南德斯群岛，其中5个属此前未在圣安布罗西奥岛被发现，进一步强化了两类群岛间的生物地理亲缘关系。
本研究凸显了对面临气候变化、外来物种入侵等多重威胁的岛屿开展调查的紧迫性，以获取基线数据，并将岛屿动物区系置于更广阔的生物地理框架中开展研究。