Okavango Research Institute, University of Botswana, Maun, Botswana.
Structure and Motion Lab, Royal Veterinary College, London, United Kingdom.
PLoS One. 2019 Mar 12;14(3):e0213720. doi: 10.1371/journal.pone.0213720. eCollection 2019.
Sympatric herbivores experience similar environmental conditions but can vary in their population trends. Identifying factors causing these differences could assist conservation efforts aimed at maintaining fully functional ecosystems. From 1996-2013, tsessebe and wildebeest populations in the Okavango Delta, Botswana, declined by 73% and 90%, respectively, whereas zebra populations remained stable. These sympatric, medium sized herbivores are exposed to similar natural and anthropogenic pressures, but apparently differ in their responses to those pressures. To identify factors that could cause these differences, we fitted GPS-enabled collars to six zebra, eight tsessebe and seven wildebeest in the Moremi Game Reserve, Botswana. We calculated utilisation distributions (UDs) from GPS data, and used 95% isopleths to compare seasonal home range size between species. We calculated utilisation intensity (UI) from the UDs and generated spatial layers representing resources and disturbances, and then used model averaging to identify factors affecting UI for each species. We calculated second and third order habitat selection ratios to determine whether species were habitat specialists or generalists. Zebra occupied larger home ranges than tsessebe and wildebeest, showed weaker responses to spatial variables and displayed no third order habitat selection; zebra social systems are also more fluid, allowing for information exchange between stable harems. Herbivore species that are sedentary, occupy small home ranges, are habitat specialists and exist in relatively isolated groups are likely to be less resistant and resilient to the rapid pace of environmental change forecast by climate change scenarios. Resources contained within existing protected areas are unlikely to maintain populations of such species at sufficiently high levels, potentially leading to functional extinction. Special precautions may be needed to ensure that such species can persist in the wild, such as buffer zones around existing protected areas, which would allow greater potential for adaptive movement should current environmental conditions change.
同域食草动物经历着相似的环境条件，但它们的种群趋势可能会有所不同。确定导致这些差异的因素，可以帮助我们进行保护工作，以维持功能完备的生态系统。1996 年至 2013 年间，博茨瓦纳奥卡万戈三角洲的斑马、角马和黑尾牛羚的数量分别下降了 73%、90%和 73%，而斑马的数量保持稳定。这些同域、中等体型的食草动物面临着相似的自然和人为压力，但它们对这些压力的反应显然不同。为了确定导致这些差异的因素，我们在博茨瓦纳的莫雷米禁猎区为 6 只斑马、8 只转角牛羚和 7 只黑尾牛羚佩戴了 GPS 项圈。我们从 GPS 数据中计算了利用度分布（UD），并使用 95%等距线比较了物种之间的季节性家域大小。我们从 UD 中计算了利用强度（UI），生成了表示资源和干扰的空间层，然后使用模型平均来确定影响每个物种 UI 的因素。我们计算了第二和第三级生境选择比，以确定物种是生境专家还是生境一般者。斑马的家域比转角牛羚和黑尾牛羚大，对空间变量的反应较弱，没有第三级生境选择；斑马的社会系统也更加灵活，允许在稳定的母群之间进行信息交流。久坐不动、占据小的家域、是生境专家且存在于相对孤立的群体中的食草动物，可能对气候变化情景预测的快速环境变化的抵抗力和恢复力较弱。现有保护区内的资源不太可能将这些物种的数量维持在足够高的水平，这可能导致功能灭绝。可能需要采取特殊措施来确保这些物种能够在野外生存，例如在现有保护区周围设置缓冲区，以便在当前环境条件发生变化时，为适应性迁移提供更大的潜力。
