Data from: Effects of divergent migratory strategies on access to resources for Cape buffalo (Syncerus caffer caffer)

Populations of large herbivores frequently display divergent migratory strategies, a likely consequence of the trade-off between the costs and benefits of migration. Globally, physical and environmental barriers disrupt migrations, leading to increased residency, which can have detrimental consequences. In the Okavango Delta, Botswana, veterinary cordon fences erected in 1982 may have caused enforced residency in some subpopulations of Cape buffalo (Syncerus caffer caffer). We used data from GPS-enabled collars fitted to females in 1 resident and 1 migratory subpopulation of buffalo to test the hypotheses that 1) residents have access to less-productive forage than migrants, 2) residents occupy smaller home ranges and live in smaller herds than migrants, 3) reproductive productivity is lower in resident herds, and 4) residents have poorer body condition than migrants. Forage characteristics varied between resident and migrant ranges, both between and within seasons. Reproductive productivity and body condition did not differ between subpopulations, but residents occupied smaller home ranges during the rainy season and lived in smaller herds than migrants. Enforced residency could have decreased carrying capacity when the fence was erected, so resident buffalo may have adapted by forming smaller herds, allowing them to maintain their body condition. The area that residents occupied was located in a more central region of the Okavango Delta than that of migrants; therefore, this area would receive higher levels of nutrients from the annual flood, which would have increased heterogeneity in resident ranges, potentially compensating for effects of disrupted migrations. These results highlight the importance of conserving landscapes with spatially and temporally heterogeneous resources to buffer effects of anthropogenic activities such as artificial barriers on migrations.

大型草食动物种群常呈现出分化的迁徙策略，这大概率是迁徙成本与收益之间权衡取舍的结果。在全球范围内，自然与环境屏障会干扰迁徙行为，导致动物滞留行为增加，进而可能产生不利影响。在博茨瓦纳奥卡万戈三角洲（Okavango Delta），1982年架设的兽医隔离围栏可能迫使部分非洲水牛（Syncerus caffer caffer）亚种群滞留原地。我们借助安装于1个滞留亚种群与1个迁徙亚种群雌性水牛身上的GPS项圈（GPS-enabled collars）所收集的数据，对以下假说进行验证：1）滞留个体可获取的饲草生产力低于迁徙个体；2）滞留个体的活动家域与兽群规模均小于迁徙个体；3）滞留兽群的繁殖生产力更低；4）滞留个体的身体状况逊于迁徙个体。饲草特征在滞留与迁徙活动范围内存在季节间与季节内的差异。两个亚种群的繁殖生产力与身体状况并无显著差异，但滞留个体在雨季的活动家域更小，且兽群规模也小于迁徙个体。围栏架设后，被迫滞留的情况可能降低了环境承载力，因此滞留水牛可能通过缩小兽群规模实现适应，从而维持自身身体状况。滞留个体的活动区域相较于迁徙个体，更靠近奥卡万戈三角洲的核心区域；因此该区域会从年度洪水获取更多养分，进而提升了滞留活动范围内的资源异质性，这可能弥补了迁徙受阻带来的负面影响。本研究结果凸显了保护具备时空异质性资源的栖息地的重要性，以此缓冲人工屏障等人类活动对动物迁徙造成的干扰。