Niche separation was documented in a year-long study of Varecia variegata rubra and Eulemur fulvus albifrons on the Masoala Peninsula, Madagascar. Feeding trees were measured, and diet, forest height, and forest site were recorded at 5-min time points on focal animals. For time point data, multivariate and bivariate analysis of frequencies was employed to examine how niche dimensions vary between species according to sex, season, and reproductive stage. V. v. rubra feeds in larger trees than E. f. albifrons. V. v. rubra has a diet consisting mainly of fruit, whereas E. f. lbifrons has a more varied diet. V. v. ubra ranges mainly above 15 m in tree crowns, whereas E. f. albifrons ranges mainly below 15 m in a wide array of forest sites. Both species are largely frugivorous, but they harvest fruit in different-sized trees, in different quantities, and in different forest strata. Niche partitioning varies in tandem with seasonal shifts in climate and food availability and with reproductive stages. Seasonal shifts in forest site and forest height use are largely attributed to species-specific tactics for behavioral thermoregulation and predator avoidance. The diet of E. f. albifrons is diverse whether examined by season or reproductive stage. However, females of both species diversify their diets with more low-fiber protein than males during gestation, lactation, and the hot seasons. This pattern is most pronounced for V. v. rubra females and may be directly attributed to high energetic investment in reproduction. These results suggest that niche partitioning may be driven more by the energetic requirements of reproductive females than males.

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The activity budgets and daily activity rhythms of Varecia rubra were examined over an annual cycle according to season and reproductive stage. Given the relatively high reproductive costs and patchy food resources of this species, I predicted that V. rubra would 1) travel less and feed more during seasonal resource scarcity in an attempt to maintain energy balance, and 2) show sex differences in activity budgets due to differing reproductive investment. Contrary to the first prediction, V. rubra does not increase feeding time during seasonal food scarcity; rather, females feed for a consistent amount of time in every season, whereas males feed most during the resource-rich, hot dry season. The results are consistent with other predictions: V. rubra travels less in the resource-scarce cold rainy season, and there are some pronounced sex differences, with females feeding more and resting less than males in every season and in every reproductive stage except gestation. However, there are also some provocative similarities between the sexes when activity budgets are examined by reproductive stage. During gestation, female and male activity budgets do not differ and appear geared toward energy accumulation: both sexes feed and rest extensively and travel least during this stage. During lactation, activity budgets are geared toward high energy expenditure: both sexes travel most and in equal measure, and rest least, although it remains the case that females feed more and rest less than males. These similarities between female and male activity budgets appear related to cooperative infant care. The high energetic costs of reproduction in V. rubra females may require that they allot more time to feeding year round, and that their overall activity budget be more directly responsive to seasonal climate change, seasonal food distribution, and reproductive schedules.

Based on a year-long field study in northeastern Madagascar, I summarize annual patterns of niche use (food patch size, diet, forest height, and forest site) in two sympatric lemurs, Varecia variegata rubra and Eulemur fulvus albifrons. Furthermore, I examine intraspecific patterns of niche use according to sex, season, and reproductive stage in these two lemurs that differ in terms of energetic investment in reproduction. Lemurs as a group provide a special opportunity to test hypotheses concerning sex differences in niche use. Due to their body size monomorphism and seasonal, synchronous pattern of breeding, it is possible to directly evaluate whether sex differences in diet reflect high energetic investment in reproduction by females. Results confirm the hypothesis that intraspecific variation in niche use (e.g., sex differences, seasonal differences) would be more pronounced in V. v. rubra than in E. f. albifrons, due in large measure to the former's relatively high energetic investment in reproduction: 1a) Dietary sex differences in V. v. rubra are most pronounced during costly reproductive stages and involve acquisition of low-fiber, high-protein plant foods. Females of both species consume more seasonally available low-fiber protein (young leaves, flowers) relative to conspecific males during the hot dry season, but only in V. v. rubra females is this pattern also evident during gestation and lactation. 1b) The diets of female V. v. rubra and female E. f. albifrons are more similar to each other than are the diets of conspecific males and females in the case of V. v. rubra. This is not uniformly the case for female E. f. albifrons. This finding confirms a hypothesis put forward in Vasey ([2000] Am J Phys Anthropol 112:411-431) that energetic requirements of reproductive females drive niche separation more than do the energetic requirements of males. 1c) Both species synchronize most or all of lactation with seasonal food abundance and diversity. E. f. albifrons shows a more protracted period of synchrony, and this may contribute to its wide biogeographic distribution in Madagascar. 2) Sex differences and seasonal differences in microhabitat use reflect intraspecific patterns of thermoregulation, predator avoidance, and in the case of V. v. rubra, reproduction. One important factor selecting for body size monomorphism in lemurs appears to be the tight synchrony between lactation and periods of food abundance afforded by annual, seasonal breeding.

Captive studies have shown that ruffed lemurs (Varecia) have an unusual suite of reproductive traits combined with extremely high maternal reproductive costs. These traits include the bearing of litters, nesting of altricial young, and absentee parenting. To characterize the breeding system of this enigmatic lemur, reproductive traits must be contextualized in the wild. Here, I provide a preliminary report of mating and infant care in one community of wild red ruffed lemurs (Varecia rubra). Observations span a 15-month period covering two birth seasons and one mating season on the Masoala Peninsula, Madagascar. Factors that are not possible to replicate in captivity are reported, such as mating pattern, natality and mortality rates, the location of nests within the home range, and the structuring of infant care within a natural community. V. rubra at Andranobe have a fission-fusion, multifemale-multimale grouping pattern and a polygamous mating system. They do not mate monogamously or live strictly in family-based groups as suggested by previous workers. During the first 2 months of life, nests and infant stashing localities are situated within each mother's respective core area, and inhabitants of each core area within the communal home range provide care for young. As part of their absentee parenting system, infants are left in concealed, protected, and supportive spots high in the canopy, while mothers travel distantly. This practice is termed 'infant stashing'. Alloparenting appears to be an integral part of V. rubra's overall reproductive strategy in the wild, as it was performed by all age-sex classes. Among the alloparental behaviors observed were infant guarding, co-stashing, infant transport, and allonursing. Alloparenting and absentee parenting may mitigate high maternal reproductive costs. Furthermore, V. rubra may have a breeding system in which genetic partners (i.e., mating partners) do not always correspond to infant care-providers. Combined with recently available information on the behavioral ecology of wild ruffed lemurs, this preliminary report suggests directions for in-depth studies on Varecia's breeding system.