Populations are typically defined as spatially contiguous sets of individuals, but large populations of social species can be composed of discrete social communities that often overlap in space. Masai giraffes (Giraffa camelopardalis tippelskirchi) of Tanzania live in distinct social subpopulations that overlap spatially, enabling us to simultaneously explore environmental and social factors correlated with demographic variation in a metapopulation of >1,400 adult females and calves. We considered statistically distinct communities in the social network as subpopulations and tested for variation among the 10 subpopulations in adult female survival, calf survival, and reproductive rate (calf-to-adult female ratio). We then related variation in demographic rates among subpopulations to differences in vegetation, soil type, proximity to 2 types of human settlements, local giraffe population density, and social metrics of relationship strength and exclusivity among adult females. We did not find any among-subpopulation effects on adult female survival, suggesting adult female survival is buffered against environmental heterogeneity among subpopulations. Variation in calf demographic rates among subpopulations were correlated with vegetation, soils, anthropogenic factors, and giraffe population density but not with adult female relationship metrics, despite substantial spatial overlap. Subpopulations with more dense bushlands in their ranges had lower calf survival probabilities, and those closer to human settlements had higher reproductive rates, possibly because of spatial gradients in natural predation. Reproductive rates were higher in subpopulations with more volcanic soils, and calf survival probabilities were greater in subpopulations with higher local adult female densities, possibly related to higher-quality habitat associated with fertile soils or lower predation risk, or to greater competitive ability. The variation in fitness among subpopulations suggests that giraffes do not move unhindered among resource patches to equalize reproductive success, as expected according to an ideal free distribution. The differences in calf survival and reproductive rates could rather indicate intercommunity differences in competitive ability, perception, learning, or experience. Our approach of comparing demography among spatially overlapping yet distinct socially defined subpopulations provides a biologically meaningful way to quantify environmental and social factors influencing fine-scale demographic variation for social species. © 2021 The Wildlife Society.

中文翻译：

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社会定义的亚群揭示了长颈鹿种群的人口统计学差异

种群通常被定义为空间上连续的个体集合，但大量的社会物种可以由离散的社会社区组成，这些社区通常在空间上重叠。马赛长颈鹿 ( Giraffa camelopardalis tippelskirchi)) 的坦桑尼亚生活在不同的社会亚群中，这些亚群在空间上重叠，使我们能够同时探索与超过 1,400 只成年雌性和小牛的复合种群中的人口变化相关的环境和社会因素。我们将社交网络中统计上不同的社区视为亚群，并测试了 10 个亚群在成年雌性存活率、小牛存活率和繁殖率（小牛与成年雌性比率）方面的差异。然后，我们将亚群之间人口统计率的变化与植被、土壤类型、与两种人类住区的接近程度、当地长颈鹿种群密度以及成年女性之间关系强度和排他性的社会指标的差异相关联。我们没有发现任何亚群间对成年女性存活率的影响，表明成年女性的生存受到亚群之间环境异质性的缓冲。尽管存在大量空间重叠，但亚群之间小牛人口统计率的变化与植被、土壤、人为因素和长颈鹿种群密度相关，但与成年雌性关系指标无关。在其范围内拥有更密集丛林的亚种群的小牛存活率较低，而那些靠近人类住区的亚种群具有更高的繁殖率，这可能是因为自然捕食的空间梯度。火山土壤较多的亚群的繁殖率更高，当地成年雌性密度较高的亚群的小牛存活率更高，这可能与肥沃的土壤或较低的捕食风险相关的高质量栖息地有关，或提高竞争力。亚群之间适应度的变化表明，长颈鹿不会在资源斑块之间不受阻碍地移动以均衡繁殖成功，正如根据理想的自由分布所预期的那样。小牛存活率和繁殖率的差异更可能表明社区间在竞争能力、感知、学习或经验方面的差异。我们比较空间重叠但具有不同社会定义的亚群之间的人口统计学的方法提供了一种具有生物学意义的方法来量化影响社会物种细尺度人口变化的环境和社会因素。© 2021 野生动物协会。根据理想的自由分布，正如预期的那样。小牛存活率和繁殖率的差异更可能表明社区间在竞争能力、感知、学习或经验方面的差异。我们比较空间重叠但具有不同社会定义的亚群之间的人口统计学的方法提供了一种具有生物学意义的方法来量化影响社会物种细尺度人口变化的环境和社会因素。© 2021 野生动物协会。根据理想的自由分布，正如预期的那样。小牛存活率和繁殖率的差异更可能表明社区间在竞争能力、感知、学习或经验方面的差异。我们比较空间重叠但具有不同社会定义的亚群之间的人口统计学的方法提供了一种具有生物学意义的方法来量化影响社会物种细尺度人口变化的环境和社会因素。© 2021 野生动物协会。我们比较空间重叠但具有不同社会定义的亚群之间的人口统计学的方法提供了一种具有生物学意义的方法来量化影响社会物种细尺度人口变化的环境和社会因素。© 2021 野生动物协会。我们比较空间重叠但具有不同社会定义的亚群之间的人口统计学的方法提供了一种具有生物学意义的方法来量化影响社会物种细尺度人口变化的环境和社会因素。© 2021 野生动物协会。