Effects of Female Group Size on the Number of Males in Blue Monkey ( Cercopithecus mitis ) Groups
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Effects of Female Group Size on the Number of Males in Blue Monkey (Cercopithecus mitis) Groups Lu Gao 1 & Marina Cords 1,2 Received: 9 January 2020 / Accepted: 28 July 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The number of males per group varies substantially in group-living primates, both between and within species. In blue monkeys (Cercopithecus mitis), males may temporarily join groups during annual mating seasons when sexually receptive females are present. A likely determinant of the number of males per group is female group size (the number of adult females in a group). To clarify the role of female group size in driving variation in the number of males per group, we expanded on earlier observations of a wild population in the Kakamega Forest, Kenya with a larger sample of groups that varied fivefold in female group size. We found considerable flexibility in social organization, with groups experiencing multimale episodes both during and outside mating seasons, some persisting over multiyear periods. The dichotomy between single- and multimale mating seasons was less distinct than previously reported, suggesting greater variation in multimale states. Across 65 group-specific conception periods, female group size strongly influenced how often multiple sexually active females and multiple males were present in a group. The number of sexually active females present on a given day related closely to the number of males in the group that same day, especially during conception periods. Results suggest that males join and remain in larger groups where mating opportunities are greater and costs of joining or staying may be lower than in smaller groups. This longitudinal study highlights intraspecific social variation within and across groups while confirming that female group size influences the number of males. Keywords Behavioral flexibility . Breeding synchrony . Intraspecific variation . Male
influx . Social organization . Male strategies
Handling Editor: Julio Cesar Bicca-Marques
* Marina Cords [email protected]
1
Department of Ecology, Evolution and Environmental Biology, Columbia University, New York, NY, USA
2
New York Consortium in Evolutionary Primatology, New York, NY, USA
L. Gao, M. Cords
Introduction The number of males in a social group is a highly variable feature of primate social organization that influences mating systems, the exchange of social behavior, and the adaptive benefits of gregarious living for members of both sexes (Kappeler 2000, 2017). Early studies of social organization often focused on the distinction between single- vs. multimale groups in cross-species comparisons (Crook and Gartlan 1966; Eisenberg et al. 1972; Emlen and Oring 1977), but awareness of intraspecific variation has grown (Agnani et al. 2018; Díaz-Muñoz and Bales 2016; Silk and Kappeler 2017; Sterck and van Hooff 2000). Such variation can occur among populations, among groups within a population, and over time in a single group (Kappeler 2017). Comparative
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