Rhinos in the Parks: An Island-Wide Survey of the Last Wild Population of the Sumatran Rhinoceros

In the 200 years since the Sumatran rhinoceros was first scientifically described (Fisher 1814), the range of the species has contracted from a broad region in Southeast Asia to three areas on the island of Sumatra and one in Kalimantan, Indonesia. Assessing population and spatial distribution of this very rare species is challenging because of their elusiveness and very low population number. Using an occupancy model with spatial dependency, we assessed the fraction of the total landscape occupied by Sumatran rhinos over a 30,345-km2 survey area and the effects of covariates in the areas where they are known to occur. In the Leuser Landscape (surveyed in 2007), the model averaging result of conditional occupancy estimate was ψ^(SE[ψ^])=0.151(0.109) or 2,371.47 km2, and the model averaging result of replicated level detection probability p^(SE[p^])=0.252(0.267); in Way Kambas National Park—2008: ψ^(SE[ψ^])=0.468(0.165) or 634.18 km2, and p^(SE[p^])=0.138(0.571); and in Bukit Barisan Selatan National Park—2010: ψ^(SE[ψ^])=0.322(0.049) or 819.67 km2, and p^(SE[p^])=0.365(0.42). In the Leuser Landscape, rhino occurrence was positively associated with primary dry land forest and rivers, and negatively associated with the presence of a road. In Way Kambas, occurrence was negatively associated with the presence of a road. In Bukit Barisan Selatan, occurrence was negatively associated with presence of primary dryland forest and rivers. Using the probabilities of site occupancy, we developed spatially explicit maps that can be used to outline intensive protection zones for in-situ conservation efforts, and provide a detailed assessment of conserving Sumatran rhinos in the wild. We summarize our core recommendation in four points: consolidate small population, strong protection, determine the percentage of breeding females, and recognize the cost of doing nothing. To reduce the probability of poaching, here we present only the randomized location of site level occupancy in our result while retaining the overall estimation of occupancy for a given area.

自1814年费舍尔（Fisher 1814）首次对苏门答腊犀牛（Sumatran rhinoceros）进行科学描述以来的200年间，该物种的分布范围已从东南亚的广阔区域萎缩至印度尼西亚苏门答腊岛的3处区域，以及加里曼丹的1处区域。由于该物种生性隐秘且种群数量极低，对其种群规模与空间分布开展评估颇具挑战。本研究采用具备空间依赖性的占用模型（occupancy model），对30345平方千米调查区域内苏门答腊犀牛的整体景观占用率，以及已知其栖息区域内的协变量影响进行了评估。在2007年调查的勒塞尔景观区，模型平均得到的条件占用估计值为ψ^(SE[ψ^])=0.151(0.109)，对应栖息面积约2371.47平方千米；模型平均得到的重复检测概率为p^(SE[p^])=0.252(0.267)。在2008年的韦坎巴斯国家公园，模型平均得到的条件占用估计值为ψ^(SE[ψ^])=0.468(0.165)，对应栖息面积约634.18平方千米，重复检测概率为p^(SE[p^])=0.138(0.571)。在2010年的武吉巴里安塞拉坦国家公园，模型平均得到的条件占用估计值为ψ^(SE[ψ^])=0.322(0.049)，对应栖息面积约819.67平方千米，重复检测概率为p^(SE[p^])=0.365(0.42)。在勒塞尔景观区，犀牛的出现概率与原生旱地森林及河流呈正相关，与道路存在呈负相关；在韦坎巴斯国家公园，犀牛出现概率与道路存在呈负相关；在武吉巴里安塞拉坦国家公园，犀牛出现概率则与原生旱地森林及河流呈负相关。基于样地占用概率，本研究绘制了空间显性地图，可用于划定原位保护（in-situ conservation）的重点防护区域，并为苏门答腊犀牛的野外保护工作提供详细评估。本研究总结了四项核心建议：整合小型种群、强化保护措施、确定繁育雌性个体占比，以及认清无所作为的保护成本。为降低偷猎风险，本研究仅在结果中公布了样地水平占用的随机位置，而保留了特定区域的占用总体估计值。