Abstract # 1024 Event # 131:

Scheduled for Friday, August 19, 2005 04:00 PM-04:15 PM: Session 10 (Mayfair Room) Oral Presentation


LIVING IN FOREST FRAGMENTS REDUCES GROUP COHESION IN DIADEMED SIFAKAS (Propithecus diadema) IN EASTERN MADAGASCAR, BY REDUCING PATCH SIZE OF FOOD RESOURCES

M. Irwin
Stony Brook University, Dept. of Anthropology, Stony Brook, NY 11794-4364, USA
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     Forest fragmentation is thought to threaten primate populations, yet the mechanisms by which this occurs remain largely unknown. I present results from a 12-month study of Propithecus diadema at Tsinjoarivo, eastern Madagascar, including two groups in rainforest fragments (FRAG) and two in continuous rainforest (CONT). Feeding data were collected continuously during all-day focal animal follows. Nearest-neighbor data were collected at 5-minute intervals (subsampled to 15-minutes to ensure independence, n = 26,792 records). CONT groups had higher dietary diversity and ate more fleshy fruit. During winter, dietary diversity dropped and they relied heavily on the small mistletoe Bakerella (diameter < 2m). In contrast, FRAG groups relied on mistletoes year-round; the fruits that sustain CONT groups throughout the summer are absent. I tested the hypothesis that habitat type affected group cohesion using categorized nearest-neighbor distances (0, 0.5-2, 3-5, 6-10 and >10m). FRAG groups had much lower cohesion (G-test, P < 0.001), with doubled median nearest-neighbor distance. For CONT groups, cohesion was highest in summer (when food patches are large), and lowest in winter (when relying on mistletoes). Chance of having no neighbor within 5m was positively correlated with percent feeding time spent on mistletoes (Spearman’s r > 0.6, P < 0.05). This suggests that fragmentation reduces group cohesion by forcing a shift to smaller food patches, possibly increasing predation risk. Supported by Margot Marsh Biodiversity Foundation, PCI, IPPL and Stony Brook University.