Geographic range size, water temperature and extrinsic threats predict the extinction risk in global cetaceans

Despite that cetaceans provide significant ecological contributions to the health and stability of aquatic ecosystems, they are highly endangered with nearly one-third of species assessed as threatened with extinction. Nevertheless, to date, few studies have explicitly examined the patterns and processes of extinction risk and threats for this taxon, and even less between the two subclades (Mysticeti and Odontoceti). To fill this gap, we compiled a dataset of six intrinsic traits (active region, geographic range size, body weight, diving depth, school size and reproductive cycle), six environmental factors relating to sea surface temperature and chlorophyll concentration, and two human-related threat indices that are commonly recognized for cetaceans. We then employed phylogenetic generalized least square (PGLS) models and model selection to identify the key predictors of extinction risk in all cetaceans, as well as in the two subclades. We found that geographic range size, sea surface temperature and human threat index were the most important predictors of extinction risk in all cetaceans and in odontocetes. Interestingly, maximum body weight was positively associated with the extinction risk in mysticetes, but negatively related to that for odontocetes. By linking seven major threat types to extinction risk, we further revealed that fisheries bycatch was the most common threat, yet the impacts of certain threats could be overestimated when considering all species rather than just threatened ones. Overall, we suggest that conservation efforts should focus on small-ranged cetaceans and species living in warmer waters or under strong anthropogenic pressures. Moreover, further studies should consider the extinction risk of species when superimposing risk maps and quantifying risk severity. Finally, we emphasize that mysticetes and odontocetes should be conserved with different strategies, because their extinction risk patterns and major threat types are considerably different. For instance, large-bodied mysticetes and small-ranged odontocetes require special conservation priority.

尽管鲸类（cetaceans）对水生生态系统的健康与稳定具有举足轻重的生态贡献，但其种群正面临严峻的濒危态势：经评估的物种中近三分之一已濒临灭绝。然而迄今为止，鲜有研究专门针对该类群的灭绝风险模式、形成过程及威胁因子展开探讨，且针对须鲸亚目（Mysticeti）与齿鲸亚目（Odontoceti）这两个亚支的比较研究更是寥寥无几。为填补这一研究空白，我们构建了一套标准化数据集，涵盖6项内在生物学性状（活动区域、地理分布范围、体重、潜水深度、群体规模与繁殖周期）、6项与海表温度及叶绿素浓度相关的环境因子，以及2项鲸类研究中常用的人为威胁指数。随后我们采用系统发育广义最小二乘（phylogenetic generalized least square, PGLS）模型与模型选择方法，分别针对全体鲸类及两个亚支群体，筛选并识别影响其灭绝风险的关键预测变量。研究结果显示，地理分布范围、海表温度与人为威胁指数，是影响所有鲸类及齿鲸类灭绝风险的核心预测因子。值得关注的是，须鲸类的最大体重与其灭绝风险呈正相关关系，而齿鲸类的最大体重则与灭绝风险呈负相关关系。通过将7类主要威胁类型与灭绝风险进行关联分析，我们进一步发现：渔业兼捕是鲸类面临的最普遍威胁，但当将全部鲸类物种而非仅濒危物种纳入分析框架时，部分威胁的影响效应可能被高估。综合上述结果，我们建议鲸类保护工作应优先聚焦于分布范围狭小的物种，以及栖息于暖水环境或面临高强度人为压力的类群。此外，后续相关研究在叠加风险地图与量化风险严重程度时，应将物种的灭绝风险纳入考量维度。最后，我们强调须鲸亚目与齿鲸亚目需采取差异化的保护策略，二者的灭绝风险模式与主要威胁类型均存在显著差异：例如，大体型须鲸与分布范围狭小的齿鲸应被赋予特殊的保护优先级。