Data from: Evaluating alternative explanations for an association of extinction risk and evolutionary uniqueness in multiple insular lineages.

Studies in insular environments have often documented a positive association of extinction risk and evolutionary uniqueness (i.e. how distant a species is from its closest living relative). However, the cause of this association is unclear. One explanation is that species threatened with extinction are evolutionarily unique because they are old, implying that extinction risk increases with time since speciation (age-dependent extinction). An alternative explanation is that such threatened species are last survivors of clades that have undergone an elevated extinction rate, and that their uniqueness results from the extinction of their close relatives. Distinguishing between these explanations is difficult but important, since they imply different biological processes determining extinction patterns. Here we designed a simulation approach to distinguish between these alternatives using living species, and applied it to twelve insular radiations that show a positive association between extinction risk and evolutionary uniqueness. We also tested the sensitivity of results to underlying assumptions and variable extinction rates. Despite differences among the radiations considered, age-dependent extinction was supported as best explaining the majority of the empirical cases. Biological processes driving characteristic changes in abundance with species duration (age-dependency) may merit further investigation.

针对岛屿环境的相关研究常证实，灭绝风险与演化独特性（evolutionary uniqueness）呈正相关关系——演化独特性指某物种与其现存最近亲缘类群的演化距离。不过，这一关联的成因仍未明晰。一种解释认为，受灭绝威胁的物种之所以演化独特，是因为其演化年代更为久远，这意味着灭绝风险会随物种形成后的时间跨度递增，即年龄依赖型灭绝（age-dependent extinction）。另一种解释则提出，这类受威胁物种乃是经历过高灭绝速率的演化支（clades）的最后残存类群，其独特性源于近缘类群的灭绝。区分这两种解释颇具难度却至关重要，因为二者所指向的决定灭绝模式的生物学过程截然不同。本研究设计了一种基于现存物种的模拟方法以区分这两种假说，并将其应用于12组呈现灭绝风险与演化独特性正相关的岛屿辐射演化类群。此外，本研究还检验了研究结果对底层假设与可变灭绝速率的敏感性。尽管所分析的辐射演化类群间存在异质性，但年龄依赖型灭绝被证实为多数实证案例的最佳解释。那些随物种存续时长（即年龄依赖性）驱动种群丰度特征性变化的生物学过程，值得开展进一步的深入研究。