Department of Biology, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada.
Cognitive and Behavioural Ecology Interdisciplinary Program, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada.
PLoS One. 2018 Mar 1;13(3):e0193425. doi: 10.1371/journal.pone.0193425. eCollection 2018.
In many taxa, individual social traits appear to be consistent across time and context, thus meeting the criteria for animal personality. How these differences are maintained in response to changes in population density is unknown, particularly in large mammals, such as ungulates. Using a behavioral reaction norm (BRN) framework, we examined how among- and within-individual variation in social connectedness, measured using social network analyses, change as a function of population density. We studied a captive herd of elk (Cervus canadensis) separated into a group of male elk and a group of female elk. Males and females were exposed to three different density treatments and we recorded social associations between individuals with proximity-detecting radio-collars fitted to elk. We constructed social networks using dyadic association data and calculated three social network metrics reflective of social connectedness: eigenvector centrality, graph strength, and degree. Elk exhibited consistent individual differences in social connectedness across densities; however, they showed little individual variation in their response to changes in density, i.e., individuals oftentimes responded plastically, but in the same manner to changes in density. Female elk had highest connectedness at an intermediate density. In contrast, male elk increased connectedness with increasing density. Whereas this may suggest that the benefits of social connectedness outweigh the costs of increased competition at higher density for males, females appear to exhibit a threshold in social benefits (e.g. predator detection and forage information). Our study illustrates the importance of viewing social connectedness as a density-dependent trait, particularly in the context of plasticity. Moreover, we highlight the need to revisit our understanding of density dependence as a population-level phenomenon by accounting for consistent individual differences not only in social connectedness, but likely in other ecological processes (e.g., predator-prey dynamics, mate choice, disease transfer).
在许多分类群中，个体的社会特征似乎在时间和环境上保持一致，因此符合动物个性的标准。这些差异如何在种群密度变化的情况下得以维持尚不清楚，特别是在大型哺乳动物（如有蹄类动物）中。利用行为反应规范（BRN）框架，我们研究了使用社会网络分析测量的社交联系的个体间和个体内差异如何随种群密度而变化。我们研究了一群圈养的麋鹿（Cervus canadensis），分为一群雄性麋鹿和一群雌性麋鹿。雄性和雌性麋鹿暴露在三种不同的密度处理下，我们记录了带有接近探测无线电项圈的个体之间的社交联系。我们使用二元关联数据构建了社会网络，并计算了三个反映社交联系的社会网络指标：特征向量中心性、图强度和度。麋鹿在不同密度下表现出一致的个体间社交联系差异；然而，它们对密度变化的反应几乎没有个体差异，即个体通常具有可塑性，但对密度变化的反应方式相同。雌性麋鹿在中等密度下具有最高的连接性。相比之下，雄性麋鹿随着密度的增加而增加连接性。虽然这可能表明，对于雄性来说，社交联系的好处大于竞争增加的代价，但雌性似乎表现出社交收益的阈值（例如，捕食者检测和觅食信息）。我们的研究说明了将社交联系视为密度依赖特征的重要性，特别是在可塑性方面。此外，我们强调需要重新审视我们对密度依赖性的理解，将其视为一种种群水平的现象，不仅要考虑社交联系的个体差异，还可能要考虑其他生态过程（例如，捕食者-猎物动态、配偶选择、疾病传播）的个体差异。
