Species flocks are proliferations of closely-related species, usually after colonization of depauperate habitat. These radiations are abundant on oceanic islands and in ancient freshwater lakes, but rare in marine habitats. This contrast is well documented in the Hawaiian Archipelago, where terrestrial examples include the speciose silverswords (sunflower family Asteraceae), Drosophila fruit flies, and honeycreepers (passerine birds), all derived from one or a few ancestral lineages. The marine fauna of Hawai'i is also the product of rare colonization events, but these colonizations usually yield only one species. Dispersal ability is key to understanding this evolutionary inequity. While terrestrial fauna rarely colonize between oceanic islands, marine fauna with pelagic larvae can make this leap in every generation. An informative exception is the marine fauna that lack a pelagic larval stage. These low-dispersal species emulate a "terrestrial" mode of reproduction (brooding, viviparity, crawl-away larvae), yielding marine species flocks in scattered locations around the world. Elsewhere, aquatic species flocks are concentrated in specific geographic settings, including the ancient lakes of Baikal (Siberia) and Tanganyika (eastern Africa), and Antarctica. These locations host multiple species flocks across a broad taxonomic spectrum, indicating a unifying evolutionary phenomenon. Hence marine species flocks can be singular cases that arise due to restricted dispersal or other intrinsic features, or they can be geographically clustered, promoted by extrinsic ecological circumstances. Here, we review and contrast intrinsic cases of species flocks in individual taxa, and extrinsic cases of geological/ecological opportunity, to elucidate the processes of species radiations.

中文翻译：

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海洋中的物种辐射：羊群是什么？

物种群是密切相关物种的增殖，通常是在贫瘠的栖息地定居之后。这些辐射在海洋岛屿和古老的淡水湖中很丰富，但在海洋栖息地中很少见。这种对比在夏威夷群岛得到了很好的记录，在那里陆地上的例子包括特殊的银剑鱼（向日葵科）、果蝇和蜜饯（雀形目鸟类），它们都来自一个或几个祖先谱系。夏威夷的海洋动物群也是罕见殖民事件的产物，但这些殖民事件通常只产生一种物种。传播能力是理解这种进化不公平的关键。虽然陆地动物群很少在海洋岛屿之间定居，但带有远洋幼虫的海洋动物群可以在每一代人中实现这一飞跃。一个提供信息的例外是缺乏远洋幼体阶段的海洋动物群。这些低扩散物种模仿“陆地”繁殖模式（育雏、胎生、爬行幼虫），在世界各地的分散地点产生海洋物种群。在其他地方，水生物种群集中在特定的地理环境中，包括贝加尔湖（西伯利亚）和坦噶尼喀（非洲东部）的古湖泊以及南极洲。这些地点在广泛的分类范围内拥有多个物种群，表明存在统一的进化现象。因此，海洋物种群可能是由于扩散受限或其他内在特征而出现的奇异情况，或者它们可能在地理上聚集，受到外在生态环境的推动。这里，