The Key to Madagascar Frugivores

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Abstract

In the Malagasy ecosystem one particular animal group, lemurs, have the greatest biomass and species richness of frugivores. The peak fruit production in the Malagasy rain forests is about three months shorter compared to peak fruit production in the Amazon and the African rain forests. This suggests that the environment in Madagascar has more well-defined constraints than other continental areas with primates. In Ranomafana National Park, both the overall number of trees, and the number of tree species producing fruit drops during winter months. Particularly in large-bodied lemurs such as sifakas, drop in fruit availability corresponds to an increase in leaf eating. In addition to dietary shifts, all lemur species appear to be able to deal with the season of scarce fruit availability by conserving energy. Extreme responses to winter season are seen in small-bodied lemurs which go into hibernation up to six months every year. Unlike many primate communities in other continents, lemurs do not have synchronous birth peaks across species. In Ranomafana sympatric lemurs show that while individuals within a species have synchronized births, across species lemurs have synchronized weaning. The weaning synchrony coincides with maximum fruit availability and production of small fruits peaks when small juvenile lemurs begin to forage independently. These patterns suggest that lemurs do not appear to rely on fruits to carry them over the period of food scarcity as would be expected from classical descriptions of keystone resources. Rather, we propose that lemurs as a guild rely on fruits as a keystone resource during the warm, wet months in order for lactation and weaning to succeed. Many of the fruit tree species used by lemurs are also hardwood species favored by selective loggers. While loss of these key fruit trees may not drive lemurs into extinction immediately, it may adversely affect reproductive success years after logging.