Lemur traits and Madagascar ecology: Coping with an island environment

The last decade's lemur research includes successes in discovering new livi ng and extinct species and learning about the distribution, biogeography, p hysiology, behavior, and ecology of previously little-studied species. In a ddition, in both the dry forest and rain forest, long-term studies of lemur demography, life history and reproduction, have been completed in conjunct ion with data on tree productivity, phenology, and climate. Lemurs contrast with anthropoids in several behavioral features, including female dominanc e, targeted female-female aggression, lack of sexual dimorphism regardless of mating system, sperm competition coupled with male-male aggression, high infant mortality, cathemerality, and strict seasonal breeding. Hypotheses to explain these traits include the "energy conservation hypothesis" (ECH) suggesting that harsh and unpredictable climate factors on the island of Ma dagascar have affected the evolution of female dominance, and the "evolutio nary disequilibrium hypotheses" (EVDH) suggesting that the recent megafauna extinctions have influenced lemurs to become diurnal. These hypotheses are compared and contrasted in light of recent empirical data on climate, subf ossils, and lemur behavior. New data on life histories of the rain forest l emurs at Ranomafana National Park give further support to the ECH. Birth se asons are synchronized within each species, but there is a 6-month distribu tion of births among species. Gestation and lactation lengths vary among sy mpatric lemurs, but all lemur species in the rain forest wean in synchrony at the season most likely to have abundant resources. Across-species weanin g synchrony seen in Ranomafana corroborates data from the dry forest that l ate lactation and weaning is the life history event that is the primary foc us of the annual schedule. Lemur adaptations may assure maximum offspring s urvival in this environment with an unpredictable food supply and heavy pre dation. In conclusion, a more comprehensive energy frugality hypothesis (EF H) is proposed, which postulates that the majority of lemur traits are eith er adaptations to conserve energy (e.g., low basal metabolic rate (BMR), to rpor, sperm competition, small group size, seasonal breeding) or to maximiz e use of scarce resources (e.g., cathemerality, territoriality, female domi nance, fibrous diet, weaning synchrony). Among primates, the isolated adapt ive radiation of lemurs on Madagascar may have been uniquely characterized by selection toward efficiency to cope with the harsh and unpredictable isl and environment. (C) 1999 Wiley-Liss, Inc.