The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)


Together in solitude: Sifakas and bamboo lemurs cycle through food patches rapidly and rarely share

MITCHELL T. IRWIN1,5, TSARAFILAMATRA ROTSINOMENA ANDRIAMISEDRA2, LAUREN BETTINO3, MOLLY C. FITZPATRICK1, TSIORINTSOA RANDRIAMASY2, NANDRIANINA RABETOANDRO2, HOLIARIMINO VOLOLONORO4 and FANOMEZANTSOA JEAN-LUC RAHARISON5.

1Department of Anthropology, Northern Illinois University, 2Department of Paleontology and Biological Anthropology, University of Antananarivo, 3Department of Environmental Conservation, University of Massachusetts Amherst, 4Department of Animal Biology, University of Antananarivo, 5Division of Research, NGO Sadabe

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Socioecology seeks to explain the evolution of social organization by modeling it as an adaptation to spatiotemporal distribution of foods. A fundamental assumption is that increasing group size causes increased feeding competition; this has been documented in several species. However, one variable that many studies overlook is the degree to which food patches are shared by groupmates. We used day-long focal animal follows to quantify patch use and sharing in two lemur species at Tsinjoarivo, Madagascar. Diademed sifakas (Propithecus diadema) visited 37.2 feeding patches per day, with average bout duration of 232s (n=363 days). For four adults in 2 groups (each with 1 adult male and 1 adult female), 15.8% of bouts were in patches shared with the other adult (17.2% of feeding time), and most sharing was sequential, not simultaneous (n=8 days). Bamboo lemurs (Hapalemur griseus) had shorter bouts (213s; n=133 days). Within a 4-member group, 64% of the adult female’s feeding time and 84% of the adult male’s was in patches not shared by groupmates (n=8 days). Lemurs (especially adults) seem to be “isolated within groups” during feeding. This raises questions for understanding optimum group size; if group-mates find similar-quality patches, the relationship between patch size and group spread may be less important than the ranging costs associated with larger groups (scramble competition). However, if similar patches are not found, steeper within-group fitness gradients may result. Much remains unknown about interspecific variation in patch-sharing; understanding these differences might help explain variation in social adaptations, including unique lemur traits.

Supported by Margot Marsh Biodiversity Foundation, National Geographic Society, NSERC, Northern Illinois University, and St. Louis Zoo