Data from: Resource selection and landscape change reveal mechanisms suppressing population recovery for the world's most endangered antelope

Understanding how bottom-up and top-down forces affect resource selection can inform restoration efforts. With a global population size of <500 individuals, the hirola Beatragus hunteri is the world's most endangered antelope, with a declining population since the 1970s. While the underlying mechanisms are unclear, some combination of habitat loss and predation are thought to be responsible for low abundances of contemporary populations. Efforts to conserve hirola are hindered by a lack of understanding as to why population density remains low, despite eradication of the viral disease, rinderpest. To elucidate factors underlying chronically low numbers, we examined resource selection and landscape change within the hirola's native range. Because hirola are grazers, we hypothesized that the availability of open areas would be linked both to forage and safety from predators. We quantified: (1) changes in tree cover across the hirola's historical range in eastern Kenya over the past 27 years; (2) how tree cover has influenced resource selection by hirola; and (3) interactions between tree cover and predation. Between 1985 and 2012, tree cover increased by 251% across the historical range of hirola. Tree encroachment was associated with a 98% decline of hirola and elephant Loxodonta africana populations, a 74% decline in cattle Bos indicus, an increase in browsing livestock by 327%, and a reduction in rainfall. Although hirola avoided tree cover, we found no evidence that predation on hirola increased with increasing tree cover. Synthesis and applications. Hirola may qualify as a refugee species, in which contemporary populations are restricted to suboptimal habitat and exhibit low survival, reproduction, or both. The extinction of hirola would be the first of a mammalian genus on the African continent in modern history. We conclude that contemporary low numbers of hirola are due at least partly to habitat loss via tree encroachment, triggered by some combination of elephant extirpation, overgrazing, drought, and perhaps fire suppression. We recommend a combination of rangeland restoration efforts (including conservation of elephants, manual clearing of trees, and grass seeding), increased enforcement of an existing protected area (Arawale National Reserve), and reintroductions to enhance recovery for this endangered species. These efforts will rely on enhanced support from the international conservation community and the cooperation of pastoralist communities with which the hirola coexist.探究自上而下与自下而上的作用力如何影响资源选择，可为物种恢复工作提供科学参考。全球种群数量不足500只的亨氏牛羚（hirola, Beatragus hunteri）是全球最濒危的羚羊物种，自20世纪70年代起种群持续衰退。尽管其种群长期偏低的内在机制尚不明确，但普遍认为栖息地丧失与捕食作用的共同影响是当代种群数量稀少的核心原因。尽管病毒性疾病牛瘟（rinderpest）已被根除，但学界对为何该物种的种群密度仍维持低位缺乏认知，这一困境阻碍了亨氏牛羚的保护工作。 为阐明该物种种群长期处于低水平的关键影响因素，我们针对亨氏牛羚原生分布区内的资源选择与景观变化展开了研究。由于亨氏牛羚为草食性动物，我们提出假说：开阔区域的可获得性同时与采食条件及躲避天敌的安全性相关。我们开展了三项量化分析：（1）解析过去27年间肯尼亚东部亨氏牛羚历史分布区内的树木覆盖度变化；（2）探究树木覆盖度对亨氏牛羚资源选择的影响；（3）解析树木覆盖度与捕食作用之间的交互关系。 1985年至2012年间，亨氏牛羚历史分布区内的树木覆盖度增长了251%。树木侵殖与亨氏牛羚和非洲象（Loxodonta africana）的种群数量下降98%、瘤牛（Bos indicus）种群数量下降74%、啃食性家畜数量增长327%以及降雨量减少存在显著关联。尽管亨氏牛羚会主动避开树木覆盖区域，但我们未发现捕食压力随树木覆盖度升高而增强的证据。 综合分析与应用启示。亨氏牛羚或可被归类为避难所物种（refugee species）——即当代种群仅能局限于次优栖息地中，且存活率、繁殖率偏低或二者兼具。亨氏牛羚的灭绝将是现代历史上非洲大陆首个哺乳动物属级物种的灭绝事件。我们认为，该物种当代种群数量偏低至少部分源于树木侵殖引发的栖息地丧失，而树木侵殖则由非洲象局部灭绝、过度放牧、干旱以及可能的火抑制等多重因素共同触发。 我们建议结合开展多项草场恢复工作（包括非洲象保护、人工伐树、草地播种）、加强现有保护区阿拉瓦莱国家保护区（Arawale National Reserve）的执法力度，以及实施再引入计划，以推动这一濒危物种的种群恢复。上述工作的推进，有赖于国际保护界的更多支持，以及与亨氏牛羚共存的游牧社区的协作配合。