Table_1_Frequency and Density Associated Grouping Patterns of Male Roosevelt Elk.DOCX

Group-size variation has been examined within a framework of costs and benefits to ecological factors such as food limitations and risks from predators. Social interactions between males from male–male competition might also influence group size particularly in polygynous males. To explore the role of social and ecological factors on group size outside the mating season I examined the influence of abundance on male grouping patterns in a population of Roosevelt elk (Cervus elaphus roosevelti) in northwestern California, USA. Male grouping patterns were complex, males often group with other males, but they also can be transient members of female groups. Because male–male competition is pervasive even outside of the mating season, sizes of groups comprised of males only should be positive and linearly related to abundance of the male population or frequency associated. Whereas the number of males in female groups should be inversely related to female abundance or density associated. Males associating with females is more likely at low female abundance because females might still be reproductively active and per capita forage should be abundant. Across a 23-year study I examined whether male or female abundance was related to male only group sizes and the number of males in female groups. Size of male-only groups displayed a positive, linear relationship with male abundance and the number of males in female groups exhibited an inverse, linear relationship with female abundance. Uncovering forces influencing male grouping patterns required using the appropriate metric of abundance. Social factors likely influenced sizes of male-only groups and ecological factors probably influenced male prevalence in female groups.

已有研究围绕食物限制、捕食者风险等生态因子的成本收益框架，对群体规模变异展开了探讨。雄性间竞争所驱动的雄性社会互动，同样可能影响群体规模，这一点在多配制雄性类群中尤为显著。为探究交配季外社会与生态因子对群体规模的作用，本研究针对美国加利福尼亚州西北部的罗斯福马鹿（Cervus elaphus roosevelti）种群，探讨了种群密度对雄性集群模式的影响。雄性集群模式较为复杂：雄性既常与其他雄性组成群体，也可作为临时成员加入雌性群体。由于雄性间竞争即使在交配季外也普遍存在，纯雄性群体的规模应与雄性种群密度或相关种群频率呈正线性相关；而雌性群体中的雄性个体数，则应与雌性种群密度或相关种群频率呈负相关。在雌性种群密度较低时，雄性更倾向于与雌性集群，这是因为此时雌性仍处于繁殖活跃期，且人均可获取的觅食资源较为充足。本研究通过一项长达23年的调查，检验了雄性或雌性种群密度分别与纯雄性群体规模、雌性群体中雄性个体数的相关性。纯雄性群体规模与雄性种群密度呈正线性相关，而雌性群体中的雄性个体数则与雌性种群密度呈负线性相关。要揭示影响雄性集群模式的驱动因素，需采用恰当的种群密度衡量指标。社会因素或对纯雄性群体规模存在影响，而生态因素则可能调控雌性群体中的雄性占比。