Clutton-Brock T H, Rose K E, Guinness F E
Department of Zoology, University of Cambridge, UK.
Proc Biol Sci. 1997 Oct 22;264(1387):1509-16. doi: 10.1098/rspb.1997.0209.
In sexually dimorphic mammals, high population density is commonly associated with increased mortality of males relative to females and with female-biased adult sex ratios. This paper investigates the consequences of these changes on the distribution of male breeding success, the intensity of competition for females and the opportunity for sexual selection. After the red deer (Cervus elaphus L.) population of the North Block of Rum (Inner Hebrides) was released from culling, female numbers rose and male numbers declined, leading to an adult sex ratio of around one male to two females. This change was the result of increased mortality of males relative to females during the first two years of life; of increased emigration rates by young males; and of reduced immigration by males from outside the study area. The increasing bias in the adult sex ratio affected the timing of breeding as well as the distribution of mating success in males. As the adult sex ratio became increasingly biased towards females, the degree of skew in mating success (calculated across all harem-holders) increased, but mature males defended harems for shorter periods and a higher proportion of males held harems. In addition, a higher proportion of calves were fathered by immigrant males and the proportion fathered by males born in the study area declined. These results support the contention that, where high population density is associated with a female-biased adult sex ratio, competition for mates is likely to decline.
在具有两性异形的哺乳动物中，高种群密度通常与雄性相对于雌性死亡率增加以及成年性别比偏向雌性有关。本文研究了这些变化对雄性繁殖成功率分布、对雌性的竞争强度以及性选择机会的影响。在鲁姆岛（内赫布里底群岛）北区块的马鹿（Cervus elaphus L.）种群停止捕杀后，雌性数量增加而雄性数量减少，导致成年性别比约为一比二。这种变化是由于在生命的头两年中雄性相对于雌性死亡率增加；年轻雄性的迁出率增加；以及来自研究区域外的雄性迁入减少。成年性别比偏差的增加影响了繁殖时间以及雄性交配成功率的分布。随着成年性别比越来越偏向雌性，交配成功率的偏斜程度（计算所有拥有妻妾群的个体）增加，但成熟雄性保卫妻妾群的时间缩短，拥有妻妾群的雄性比例更高。此外，更高比例的幼崽由迁入雄性所生，而由研究区域内出生的雄性所生的比例下降。这些结果支持了这样的观点，即在高种群密度与成年性别比偏向雌性相关的情况下，对配偶的竞争可能会减少。
