Data from: Patterns of mammalian population decline inform conservation action

1. Evaluations of wildlife population dynamics have the potential to convey valuable information on the type of pressure affecting a population and could help predict future changes in the population's trajectory. Greater understanding of different patterns of population declines could provide a useful mechanism for assessing decline severity in the wild and identifying those populations that are more likely to exhibit severe declines. 2. We identified 93 incidences of decline within 75 populations of mammalian species using a time-series analysis method. These included: linear, quadratic convex (accelerating) declines, exponential concave (decelerating) declines, and quadratic concave declines (representing recovering populations). Excluding linear declines left a dataset of 85 declines to model the relationship between each decline-curve type and a range of biological, anthropogenic, and time-series descriptor explanatory variables. 3. None of the decline-curve types were spatially or phylogenetically clustered. The only characteristic that could be consistently associated with any curve-type was the time at which they were more likely to occur within a time-series. Quadratic convex declines were more likely to occur at the start of the time-series, while recovering curve shapes (quadratic concave declines) were more likely at the end of the time-series. 4. Synthesis and applications: The ability to link certain factors with specific decline dynamics across a number of mammalian populations is useful for management purposes as it provides decision-makers with potential triggers upon which to base their conservation actions. We propose that the identification of quadratic convex declines could be used as an early-warning signal of potentially severe decline dynamics. For such populations, increased population monitoring effort should be deployed to diagnose the cause of its decline and avert possible extinctions. Conversely, the presence of a quadratic concave decline suggests that the population has already undergone a period of serious decline but is now in the process of recovery. Such populations will require different types of conservation actions, focussed on enhancing their chances of recovery.

1. 野生动物种群动态评估可传递影响种群的各类压力类型相关的宝贵信息，同时能够助力预测种群数量变化轨迹的未来态势。对种群下降不同模式的深入认知，可为野外种群下降严重程度的评估，以及甄别更易发生严重下降的种群提供可靠的分析框架。
2. 本研究采用时间序列分析（time-series analysis）方法，在75个哺乳动物物种种群中识别出93次种群下降事件，涵盖线性下降、二次凸型（加速型）下降、指数凹型（减速型）下降，以及二次凹型下降（代表种群正处于恢复阶段）。排除线性下降事件后，本数据集剩余85次下降事件，用于构建各下降曲线类型与一系列生物学、人为干扰及时间序列描述性解释变量之间的关联模型。
3. 各类下降曲线类型均未呈现空间或系统发育聚集特征。唯一能与各曲线类型持续关联的特征，是其在时间序列中更易出现的时段：二次凸型下降更易出现在时间序列的初始阶段，而代表种群恢复的二次凹型下降曲线则更常出现于时间序列的末尾阶段。
4. 综合与应用：在多个哺乳动物种群中，将特定因素与特异性种群下降动态建立关联的能力，可为种群管理提供有力支撑——这可为决策者提供制定保护行动的潜在触发依据。本研究提出，可将二次凸型下降的识别作为潜在严重下降动态的早期预警信号；针对此类种群，应加大种群监测力度，以诊断其下降原因并规避潜在的灭绝风险。反之，二次凹型下降的出现则表明该种群此前经历了一段时期的严重下降，但目前正处于恢复进程中，此类种群则需要采取针对性的保护措施，以提升其恢复成功率。