Department of Animal and Poultry Science, College of Agriculture and Bioresources, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
PLoS One. 2013;8(1):e53777. doi: 10.1371/journal.pone.0053777. Epub 2013 Jan 9.
Density dependence can have marked effects on social behaviors such as group size. We tested whether changes in population density of a large herbivore (elk, Cervus canadensis) affected sex-specific group size and whether the response was density- or frequency-dependent. We quantified the probability and strength of changes in group sizes and dispersion as population density changed for each sex. We used group size data from a population of elk in Manitoba, Canada, that was experimentally reduced from 1.20 to 0.67 elk/km(2) between 2002 and 2009. Our results indicated that functional responses of group size to population density are sex-specific. Females showed a positive density-dependent response in group size at population densities ≥0.70 elk/km(2) and we found evidence for a minimum group size at population density ≤0.70 elk/km(2). Changes in male group size were also density-dependent; however, the strength of the relationship was lower than for females. Density dependence in male group size was predominantly a result of fusion of solitary males into larger groups, rather than fusion among existing groups. Our study revealed that density affects group size of a large herbivore differently between males and females, which has important implications for the benefits e.g., alleviating predation risk, and costs of social behaviors e.g., competition for resources and mates, and intra-specific pathogen transmission.
密度制约因素对社会行为（如群体大小）有显著影响。我们检验了大型食草动物（麋鹿，Cervus canadensis）的种群密度变化是否会影响雌雄个体的群体大小，以及这种反应是密度依赖还是频率依赖的。我们量化了种群密度变化时每个性别群体大小和分散度的变化概率和强度。我们使用了来自加拿大马尼托巴省的麋鹿种群的群体大小数据，该种群在 2002 年至 2009 年间从 1.20 只/平方公里实验性减少到 0.67 只/平方公里。我们的结果表明，群体大小对种群密度的功能反应是雌雄特异性的。在种群密度≥0.70 只/平方公里时，雌性群体大小呈现出正密度依赖性反应，我们发现种群密度≤0.70 只/平方公里时存在最小群体大小。雄性群体大小的变化也与密度有关；然而，这种关系的强度低于雌性。雄性群体大小的密度依赖性主要是由于独居雄性融合成更大的群体，而不是现有群体之间的融合。我们的研究表明，密度对大型食草动物的雌雄个体的群体大小有不同的影响，这对社会行为的益处（例如，减轻捕食风险）和成本（例如，资源和配偶竞争，以及种内病原体传播）有重要影响。
