Phylogenetic Analysis of Conservation Priorities for Aquatic Mammals and Their Terrestrial Relatives, with a Comparison of Methods

BackgroundHabitat loss and overexploitation are among the primary factors threatening populations of many mammal species. Recently, aquatic mammals have been highlighted as particularly vulnerable. Here we test (1) if aquatic mammals emerge as more phylogenetically urgent conservation priorities than their terrestrial relatives, and (2) if high priority species are receiving sufficient conservation effort. We also compare results among some phylogenetic conservation methods. Methodology/Principal FindingsA phylogenetic analysis of conservation priorities for all 620 species of Cetartiodactyla and Carnivora, including most aquatic mammals. Conservation priority ranking of aquatic versus terrestrial species is approximately proportional to their diversity. However, nearly all obligated freshwater cetartiodactylans are among the top conservation priority species. Further, ∼74% and 40% of fully aquatic cetartiodactylans and carnivores, respectively, are either threatened or data deficient, more so than their terrestrial relatives. Strikingly, only 3% of all ‘high priority’ species are thought to be stable. An overwhelming 97% of these species thus either show decreasing population trends (87%) or are insufficiently known (10%). Furthermore, a disproportional number of highly evolutionarily distinct species are experiencing population decline, thus, such species should be closely monitored even if not currently threatened. Comparison among methods reveals that exact species ranking differs considerably among methods, nevertheless, most top priority species consistently rank high under any method. While we here favor one approach, we also suggest that a consensus approach may be useful when methods disagree. Conclusions/SignificanceThese results reinforce prior findings, suggesting there is an urgent need to gather basic conservation data for aquatic mammals, and special conservation focus is needed on those confined to freshwater. That evolutionarily distinct—and thus ‘biodiverse’—species are faring relatively poorly is alarming and requires further study. Our results offer a detailed guide to phylogeny-based conservation prioritization for these two orders.研究背景 栖息地丧失与过度开发是威胁众多哺乳动物种群存续的首要因素之一。近期，水生哺乳动物被证实尤其脆弱。本研究旨在验证两个核心问题：其一，水生哺乳动物是否较其陆生近亲具有更高的系统发育保护优先级；其二，高优先级保护物种是否获得了充足的保护投入。此外，我们还对多种系统发育保护分析方法的结果进行了对比。 研究方法与主要结果 本研究针对鲸偶蹄目（Cetartiodactyla）与食肉目（Carnivora）共计620个物种开展了保护优先级的系统发育分析，研究样本涵盖绝大多数水生哺乳动物。结果显示，水生与陆生物种的保护优先级排名大致与其物种多样性呈正比。然而，几乎所有专性淡水鲸偶蹄目物种均位列顶级保护优先级物种之列。进一步分析表明，完全水生的鲸偶蹄目物种与食肉目物种中，分别有约74%与40%处于受威胁或数据缺乏状态，该比例显著高于其陆生近亲。值得注意的是，仅3%的‘高优先级’物种被认为种群趋势稳定，换言之，97%的高优先级物种要么呈现种群数量下降趋势（占比87%），要么相关基础数据不足（占比10%）。此外，进化独特性较高的物种出现种群下降的比例异常偏高，因此即便当前未受威胁，这类物种也应被纳入重点监测范围。不同保护分析方法间的对比结果显示，物种的精确优先级排名存在显著差异，但多数顶级优先级物种在各类方法下均能保持较高排名。尽管本研究倾向于某一种分析框架，但我们同时建议，当不同方法结果出现分歧时，采用共识性分析方案将具有实用价值。 研究结论与意义 本研究结果印证了此前的相关发现，表明亟需针对水生哺乳动物开展基础保护数据的收集工作，并应对淡水生境的水生哺乳动物给予特殊保护关注。进化独特性强——即所谓的‘生物多样性关键类群’——的物种生存状况普遍较差，这一现象令人担忧，有待进一步深入研究。本研究为鲸偶蹄目与食肉目这两个类群的系统发育导向保护优先级划分提供了详尽的参考指南。