Female feeding competition in a folivorous primate (Propithecus verreauxi) with formalized dominance hierarchies: contest or scramble?

Feeding competition limits female reproductive success and is expected to have social consequences for group living females. Frugivores have been argued to experience contest competition and thus are predicted to exhibit rank related asymmetries in fitness. Folivores, in contrast, are often assumed to experience scramble competition, and female fitness is predicted to be influenced by group size. Verreaux’s sifaka (Propithecus verreauxi) are a medium-sized, gregarious folivore that has been suggested to exhibit a “dispersal-egalitarian” competitive regime and experience scramble feeding competition. However, linear, formalized dominance relationships occur in females. Therefore, I examined six years of behavioral and morphological data from four social groups to determine the type of feeding competition in Verreaux’s sifaka in Kirindy Mitea National Park. Consistent with contest feeding competition, females had formal dominance relationships, expressed via unidirectional submissive signals. However, rates of agonism were not predicted by the proportion of fruit or young leaves in the diet. Female rank also did not predict female body mass indices or infant survival. In addition, contrary to expectations of scramble competition, group size did not significantly influence female body mass indices or infant survival. While group size significantly influenced nearest neighbor distances, nearest neighbor distances decreased with increasing group size, contrary to expectations. Thus, my results indicate that female Verreaux’s sifaka experience weak feeding competition and suggest that formalized dominance relationships are driven by factors other than competition for food resources.