School of Biological and Conservation Sciences, University of KwaZulu-Natal, Durban, South Africa.
PLoS One. 2010 Sep 20;5(9):e12758. doi: 10.1371/journal.pone.0012758.
Group dynamics of gregarious ungulates in the grasslands of the African savanna have been well studied, but the trade-offs that affect grouping of these ungulates in woodland habitats or dense vegetation are less well understood. We examined the landscape-level distribution of groups of blue wildebeest, Connochaetes taurinus, and Burchell's zebra, Equus burchelli, in a predominantly woodland area (Karongwe Game Reserve, South Africa; KGR) to test the hypothesis that group dynamics are a function of minimizing predation risk from their primary predator, lion, Panthera leo.
METHODOLOGY/PRINCIPAL FINDINGS: Using generalized linear models, we examined the relative importance of habitat type (differing in vegetation density), probability of encountering lion (based on utilization distribution of all individual lions in the reserve), and season in predicting group size and composition. We found that only in open scrub habitat, group size for both ungulate species increased with the probability of encountering lion. Group composition differed between the two species and was driven by habitat selection as well as predation risk. For both species, composition of groups was, however, dominated by males in open scrub habitats, irrespective of the probability of encountering lion.
CONCLUSIONS/SIGNIFICANCE: Distribution patterns of wildebeest and zebra groups at the landscape level directly support the theoretical and empirical evidence from a range of taxa predicting that grouping is favored in open habitats and when predation risk is high. Group composition reflected species-specific social, physiological and foraging constraints, as well as the importance of predation risk. Avoidance of high resource open scrub habitat by females can lead to loss of foraging opportunities, which can be particularly costly in areas such as KGR, where this resource is limited. Thus, landscape-level grouping dynamics are species specific and particular to the composition of the group, arising from a tradeoff between maximizing resource selection and minimizing predation risk.
在非洲大草原的草原上，群居有蹄类动物的群体动态已经得到了很好的研究，但在林地栖息地或茂密植被中影响这些有蹄类动物群体形成的权衡因素却了解较少。我们检查了主要为林地（南非 Karongwe 野生动物保护区；KGR）中蓝角马 Connochaetes taurinus 和斑驴 Equus burchelli 群体的景观水平分布，以检验以下假设：即群体动态是最小化来自其主要捕食者狮子 Panthera leo 的捕食风险的函数。
方法/主要发现：我们使用广义线性模型，检查了栖息地类型（植被密度不同）、遇到狮子的概率（基于保护区内所有个体狮子的利用分布）和季节在预测群体大小和组成方面的相对重要性。我们发现，只有在开阔灌丛栖息地中，两种有蹄类动物的群体大小才会随着遇到狮子的概率增加而增加。群体组成在这两个物种之间存在差异，这是由栖息地选择和捕食风险驱动的。对于这两个物种，在开阔灌丛栖息地中，无论遇到狮子的概率如何，群体组成都以雄性为主。
结论/意义：在景观水平上，角马和斑马群体的分布模式直接支持了从一系列分类单元得出的理论和经验证据，这些证据预测了在开阔栖息地和捕食风险高的情况下，群体形成是有利的。群体组成反映了物种特有的社会、生理和觅食限制，以及捕食风险的重要性。雌性避免高资源开阔灌丛栖息地可能会导致觅食机会的丧失，在像 KGR 这样资源有限的地区，这可能特别昂贵。因此，景观水平的群体动态是特定于物种的，并且与群体的组成有关，这是在最大化资源选择和最小化捕食风险之间的权衡。
