Van Belle Sarie, Estrada Alejandro
Department of Zoology, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Am J Primatol. 2008 Jun;70(6):613-9. doi: 10.1002/ajp.20534.
It has been argued that grouping patterns might influence the reproductive performance of individuals. Increasing group size results in greater travel costs and competition over depletable food resources, which could lead to reduced individual reproductive success. However, in groups with an increasing number of males, female reproductive success is predicted to augment because larger male groups might better protect immatures from infanticidal attacks. In contrast, male reproductive success is predicted to decrease with number of males in a group because fertilization cannot be shared between males. In this paper, we test these predictions on the Mesoamerican black howler monkey (Alouatta pigra) with data on group size and composition for 120 groups from eight populations of black howler monkeys existing in eight protected forests in Mexico and Guatemala. Male and female reproductive success were calculated as a deviation of the observed number of infants (or immatures) from the expected number of infants (or immatures), relative to the number of males and females in a group. Results indicate that both male and female reproductive success decreased with group size. Male reproductive success decreased with an increasing number of males in a group and with increasing proportion of males relative to females in a group. Decreased female reproductive success was associated with increasing number of females in a group, and female reproductive success had a tendency to increase with increasing number of males in a group. These results suggest that in black howler monkeys, living in larger groups might negatively affect the reproductive success of each member. Our findings are similar to those reported for a population of a sister species, Alouatta palliata, living in larger groups.
有人认为，群体模式可能会影响个体的繁殖表现。群体规模的增加会导致更高的出行成本以及对可耗尽食物资源的竞争加剧，这可能会导致个体繁殖成功率降低。然而，在雄性数量不断增加的群体中，预计雌性繁殖成功率会提高，因为更大的雄性群体可能会更好地保护幼崽免受杀婴攻击。相比之下，预计雄性繁殖成功率会随着群体中雄性数量的增加而降低，因为雄性之间无法共享受精机会。在本文中，我们利用来自墨西哥和危地马拉八个受保护森林中八个黑吼猴种群的120个群体的群体规模和组成数据，对这些预测进行了检验。雄性和雌性繁殖成功率的计算方法是，观察到的幼崽（或未成熟个体）数量与预期数量的偏差，相对于群体中的雄性和雌性数量而言。结果表明，雄性和雌性繁殖成功率均随群体规模的增加而降低。雄性繁殖成功率随着群体中雄性数量的增加以及雄性相对于雌性比例的增加而降低。雌性繁殖成功率的降低与群体中雌性数量的增加有关，并且雌性繁殖成功率有随着群体中雄性数量的增加而增加的趋势。这些结果表明，对于黑吼猴来说，生活在更大的群体中可能会对每个成员的繁殖成功率产生负面影响。我们的研究结果与报道的一个姐妹物种——鬃毛吼猴（Alouatta palliata）种群生活在更大群体中的情况相似。
