Behavioral plasticity, or the mechanism by which an organism can adjust its behavior in response to exogenous change, has been highlighted as a potential buffer against extinction risk. Giraffes (Giraffa spp.) are gregarious, long-lived, highly mobile megaherbivores with a large brain size, characteristics that have been associated with high levels of behavioral plasticity. However, while there has been a recent focus on genotypic variability and morphological differences among giraffe populations, there has been relatively little discussion centered on behavioral flexibility within giraffe populations. In large wild herbivores, one measure of behavioral plasticity is the ability to adjust herd size in line with local environmental conditions. Here, we examine whether a genetically isolated population of Angolan giraffes (G. g. angolensis) in a heterogeneous environment adjust their herd sizes in line with spatiotemporal variation in habitat. Our results suggest that ecological factors play a role in driving herd size, but that social factors also shape and stabilize herd-size dynamics. Specifically, we found that 1) mixed-sex herds were larger than single-sex herds, suggesting that sexual composition of herds played a role in driving herd size; 2) the presence of young did not influence herd size, suggesting that giraffes did not make use of the dilution effect to safeguard their young from predation; and 3) there was a strong relationship between herd size and spatial, but not seasonal, variation in food biomass availability, suggesting stability in herd sizes over time, but temporary variation in line with resource availability. These findings indicate that giraffes adjust herd size in line with local exogenous factors, signaling high behavioral plasticity, but also suggest that this mechanism operates within the constraints of the social determinants of giraffe herd size.

中文翻译：

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栖息地异质性和社会因素驱动长颈鹿群规模动态的行为可塑性

行为可塑性，或生物体可以根据外源性变化调整其行为的机制，已被强调为抵御灭绝风险的潜在缓冲。长颈鹿 (Giraffa spp.) 是群居的、长寿的、高度移动的大型食草动物，具有较大的大脑尺寸，这些特征与高水平的行为可塑性有关。然而，虽然最近关注长颈鹿种群之间的基因型变异和形态差异，但关于长颈鹿种群内行为灵活性的讨论相对较少。在大型野生食草动物中，行为可塑性的一种衡量标准是根据当地环境条件调整畜群规模的能力。在这里，我们检查基因上孤立的安哥拉长颈鹿种群（G. g. angolensis）在异质环境中根据栖息地的时空变化调整其畜群规模。我们的研究结果表明，生态因素在驱动畜群规模方面发挥作用，但社会因素也会塑造和稳定畜群规模动态。具体来说，我们发现 1) 混合性别的牛群比单一性别的牛群大，这表明牛群的性别构成在驱动牛群规模方面发挥了作用；2) 幼仔的存在不影响种群规模，表明长颈鹿没有利用稀释效应来保护幼仔免受捕食；3) 畜群规模与食物生物量可用性的空间变化（而非季节性）之间存在密切关系，这表明畜群规模随时间保持稳定，但与资源可用性一致的暂时变化。