The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Preliminary evidence suggests that two-male siamang (Symphalangus syndactylus) groups at Way Canguk live in larger, higher quality home ranges than monogamous groups


1Anthropology, Appalachian State University, 2Anthropology, Rutgers University, 3International Programs, Wildlife Conservation Society, 4Mpala Research Centre, Mpala Wildlife Foundation, 5Biology, Universitas Indonesia

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Siamang groups at Way Canguk contain one adult female but one, two, or occasionally three adult males. Food abundance and distribution affect grouping patterns in many animal populations, but the effects of ecological factors on siamang group dynamics are poorly understood. We examined the relationship between group composition, home range size, and an indirect measure of habitat quality to test the hypothesis that home range size and quality are important predictors of grouping patterns at Way Canguk.

Group composition and ranging data were collected from 11 groups from 2000-2002 (7 groups) and 2007-2009 (11 groups). We collected feeding data from 6 groups from 2000-2002.

Home range size was a near-significant predictor of the number of males in a group (GLMM with group as a random factor; F1,13.8=4.2, P=0.060). However, there was not a significant relationship between home range size and the density (feeding trees/ha) of important food trees used by the siamangs (rs=-0.143, N=6, P=0.787). Thus, larger home ranges should contain more food, and indeed, groups that contained more males fed from more important food trees (rs = 0.851, N=6, P=0.016). Groups containing more males also contained more infants and juveniles (F1,15.9=14.0, P=0.002), suggesting that birth rates, offspring survivorship, or both were higher in multi-male groups. Alternatively, the association between reproductive rates and the number of males in a group may be driven by underlying relationships between both variables and home range quality. Our results may shed light on the determinants of group composition in primates.

Funding was provided by the USA Fulbright Program, the LSB Leakey Foundation, Sigma Xi, the Wenner-Gren Foundation, the National Science Foundation (Grant ID 0726022 to LM), Appalachian State University, Rutgers University, and Wildlife Conservation Society-Indonesia Program.

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