Kabalika Zabibu, Morrison Thomas A, McGill Rona A R, Munishi Linus K, Ekwem Divine, Mahene Wilson Leonidas, Lobora Alex L, Newton Jason, Morales Juan M, Haydon Daniel T, Hopcraft Grant G J C
Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Graham Kerr building, Glasgow, G12 8QQ UK.
National Environmental Isotope Facility, Scottish Universities Environmental Research Centre, University of Glasgow, Glasgow, G75 0QF UK.
Mov Ecol. 2020 Sep 18;8:37. doi: 10.1186/s40462-020-00222-w. eCollection 2020.
Current animal tracking studies are most often based on the application of external geolocators such as GPS and radio transmitters. While these technologies provide detailed movement data, they are costly to acquire and maintain, which often restricts sample sizes. Furthermore, deploying external geolocators requires physically capturing and recapturing of animals, which poses an additional welfare concern. Natural biomarkers provide an alternative, non-invasive approach for addressing a range of geolocation questions and can, because of relatively low cost, be collected from many individuals thereby broadening the scope for population-wide inference.
We developed a low-cost, minimally invasive method for distinguishing between local versus non-local movements of cattle using sulfur isotope ratios (δS) in cattle tail hair collected in the Greater Serengeti Ecosystem, Tanzania.
We used a Generalized Additive Model to generate a predicted δS isoscape across the study area. This isoscape was constructed using spatial smoothers and underpinned by the positive relationship between δS values and lithology. We then established a strong relationship between δS from recent sections of cattle tail hair and the δS from grasses sampled in the immediate vicinity of an individual's location, suggesting δS in the hair reflects the δS in the environment. By combining uncertainty in estimation of the isoscape, with predictions of tail hair δS given an animal's position in the isoscape we estimated the anisotropic distribution of travel distances across the Serengeti ecosystem sufficient to detect movement using sulfur stable isotopes.
While the focus of our study was on cattle, this approach can be modified to understand movements in other mobile organisms where the sulfur isoscape is sufficiently heterogeneous relative to the spatial scale of animal movements and where tracking with traditional methods is difficult.
当前的动物追踪研究大多基于全球定位系统（GPS）和无线电发射器等外部定位器的应用。虽然这些技术能提供详细的移动数据，但获取和维护成本高昂，这常常限制了样本量。此外，部署外部定位器需要对动物进行物理捕捉和重新捕捉，这带来了额外的福利问题。天然生物标志物提供了一种替代的、非侵入性的方法来解决一系列地理定位问题，并且由于成本相对较低，可以从许多个体中收集，从而扩大了进行全种群推断的范围。
我们开发了一种低成本、微创的方法，利用在坦桑尼亚大塞伦盖蒂生态系统收集的牛尾毛中的硫同位素比率（δS）来区分牛的本地移动和非本地移动。
我们使用广义相加模型生成了研究区域内预测的δS等硫值图。该等硫值图是使用空间平滑器构建的，并以δS值与岩性之间的正相关关系为基础。然后，我们在牛尾毛最近部分的δS与个体所在位置附近采集的草的δS之间建立了紧密的关系，这表明毛发中的δS反映了环境中的δS。通过将等硫值图估计中的不确定性与给定动物在等硫值图中的位置时尾毛δS的预测相结合，我们估计了塞伦盖蒂生态系统中旅行距离的各向异性分布，足以利用硫稳定同位素检测移动情况。
虽然我们的研究重点是牛，但这种方法可以进行修改，以了解其他移动生物的移动情况，前提是硫等硫值图相对于动物移动的空间尺度具有足够的异质性，且传统方法难以进行追踪。
