Asian elephant microsatellite genotypes: Nakai Plateau and Sepon mines region, Lao PDR

Habitat loss and fragmentation are leading contributors to the endangered status of species. In 2006, the Nakai Plateau contained the largest known Asian elephant (Elephas maximus) population in the Lao People's Democratic Republic (Lao PDR), and the population was among those with the highest genetic diversity reported for Asian elephants. In 2008, completion of the Nam Theun 2 hydroelectric dam inundated much of the Plateau, resulting in the loss of 40% of elephant habitat. We studied elephant presence, movements, and the incidence of human–elephant conflict (HEC) on the Nakai Plateau and surrounding areas from 2004-2020, before and for 12 years after dam completion. To examine contemporary population dynamics in the Nakai elephants, we used genetic sampling to compare minimum population numbers, demography, and levels of genetic diversity from the wet and dry seasons in 2018/2019, 10 years after dam completion, with those reported in a pre-dam-completion genetic survey. After dam completion, we found a major increase in HEC locally and the creation of new, serious, and persistent HEC problems as far as 100 km away. While we were unable to compare estimated population sizes before and after dam completion, our data revealed a decrease in genetic diversity, a male-biased sex ratio, and evidence of dispersal from the Plateau by breeding-age females. Our results raise concerns about the long-term viability of this important population as well as that of other species in this region. Given that hydropower projects are of economic importance throughout Laos and elsewhere in southeast Asia, this study has important implications for understanding and mitigating their impact.

栖息地丧失与破碎化是导致物种濒危的主要诱因。2006年，老挝人民民主共和国（Lao People's Democratic Republic, Lao PDR）南凯高原拥有当时已知规模最大的亚洲象（Elephas maximus）种群，该种群的遗传多样性水平位列已报道的亚洲象种群前列。2008年，南俄2水电站大坝建成蓄水，淹没了高原大片区域，导致该区域40%的亚洲象栖息地丧失。
本研究于2004—2020年（涵盖大坝建成前的基线监测阶段与大坝建成后12年的跟踪监测阶段），针对南凯高原及其周边区域开展了亚洲象种群存在性、移动模式与人象冲突（human–elephant conflict, HEC）发生情况的调查。为解析南凯高原亚洲象的当代种群动态，我们于大坝建成10年后的2018/2019年开展了干湿季遗传取样，对比了该时段的最小种群数量、种群统计学特征与遗传多样性水平，并与大坝建成前的遗传调查结果进行了比对。
研究结果显示，大坝建成后当地人象冲突显著加剧，且在距离该区域最远100公里的范围内均出现了新的、严重且持续的人象冲突问题。尽管我们未能直接对比大坝建成前后的种群规模估算结果，但数据显示该种群的遗传多样性有所下降，性别比例偏向雄性，同时存在育龄雌性个体从高原向外扩散的迹象。
本研究结果对该重要种群以及本区域其他物种的长期生存能力提出了警示。鉴于水电项目在老挝及东南亚其他地区均具有重要经济价值，本研究对于理解并减缓水电项目的生态影响具有重要借鉴意义。