Trophic scaling and occupancy analysis reveals a lion population limited by human pressure in the Limpopo National Park, Mozambique.

Trophic scaling and occupancy analysis reveals a lion population limited by human pressure in the Limpopo National Park, Mozambique. Authors: Kristoffer T. Everatt1*, Leah Andresen1 , Michael J. Somers1,2 Affiliations: Centre for Wildlife Management, University of Pretoria, Pretoria, South AfricaCentre for Invasion Biology, University of Pretoria, Pretoria, South Africa *To whom correspondence should be addressed: [e-mail] Abstract The African lion (Panthera leo) has suffered drastic population and range declines over the last few decades and is listed by the IUCN as vulnerable to extinction. Conservation management requires reliable population estimates, however these data are lacking for many of the continent’s remaining lion populations. It is possible to estimate lion populations using a trophic scaling approach based on relatively easy to obtain aerial prey data. However, such inferences assume that a predator population is subject only to bottom-up regulation, and are thus likely to produce biased estimates in systems with considerable top-down anthropogenic pressures. Here we provide baseline data on the status of lions in a developing National Park in Mozambique that is impacted by humans and livestock. We compare a direct density estimate using call-ups with an estimate derived from trophic scaling. We then use replicated detection/non-detection surveys to estimate the proportion of area occupied by lions, and hierarchical ranking of covariates to provide inferences on the relative contribution of prey resources and anthropogenic factors influencing lion occurrence. Direct density estimates were less than 1/3 of the estimate derived from prey resources (0.99 lions/100 km2 vs. 3.05 lions/100 km2). The proportion of area occupied by lions was Ψ = 0.436 (SE = 0.127), or approximately 44% of a 2400 km2 sample of potential habitat. Although lions were strongly predicted by a greater probability of encountering prey resources, the greatest contributing factor to lion occurrence was a strong negative association with agro-pastoralist settlement areas. Finally, our empirical abundance estimate is approximately a third of a published abundance estimate derived from opinion surveys. Altogether, our results describe a lion population that is held below resource-based carrying capacity by anthropogenic factors, and highlight the limitations of trophic scaling and opinion surveys for estimating predator populations exposed to anthropogenic pressures. Our study provides the first empirical quantification of a population that future change can be measured against.

营养级缩放（trophic scaling）与占用分析（occupancy analysis）揭示莫桑比克林波波国家公园内受人类压力制约的狮子种群
作者：Kristoffer T. Everatt¹*，Leah Andresen¹，Michael J. Somers¹,²
作者单位：1. 南非比勒陀利亚大学野生动物管理中心；2. 南非比勒陀利亚大学生物入侵研究中心
*通讯作者：[e-mail]
摘要：非洲狮（Panthera leo）在过去数十年间经历了种群数量与分布范围的大幅缩减，被世界自然保护联盟（International Union for Conservation of Nature, IUCN）列为易危物种。保护管理工作亟需可靠的种群估算数据，但非洲大陆多数残存狮种群均缺乏此类观测数据。基于易于获取的航空猎物调查数据（aerial prey data），可通过营养级缩放法（trophic scaling approach）估算狮种群数量。然而此类推断默认捕食者种群仅受上行调控（bottom-up regulation）影响，因此在存在显著人为自上而下压力（top-down anthropogenic pressures）的生态系统中，该方法得到的估算结果可能存在偏差。本研究针对莫桑比克一处受人类与家畜活动影响的发展中国家公园，提供其境内狮种群现状的基准观测数据。我们对比了基于叫声回放法（call-ups）的直接密度估算值与营养级缩放法得到的估算结果；随后通过重复检测-非检测调查（detection/non-detection surveys），估算狮子的区域占用比例，并对协变量进行层级重要性排序（hierarchical ranking of covariates），以推断猎物资源与人为因素对狮子出现概率的相对贡献。直接密度估算值仅为基于猎物资源得到的估算值的1/3以下（0.99头/100 km² vs. 3.05头/100 km²）。狮子的区域占用比例为Ψ=0.436（标准误SE=0.127），即2400 km²潜在栖息地中约44%的区域被狮子占据。尽管猎物资源丰度更高的区域更易观测到狮子，但影响狮子出现的最主要因素为其与农牧民定居点存在显著负相关关系。此外，本研究得到的实测种群数量估算值仅为已发表的基于专家意见调查的种群丰度估算值的1/3左右。综上，我们的研究结果表明，人为因素将狮种群压制在基于资源的环境容纳量（carrying capacity）之下，同时凸显了营养级缩放法与意见调查在估算受人为压力影响的捕食者种群时存在的局限性。本研究提供了首个可用于衡量未来种群变化的基准量化数据。