Tim Bransford

Lemurs are severely threatened due to anthropogenic habitat loss and climate change. Therefore, understanding how lemurs adapt their diets to novel habitats is critically important for maintaining healthy wild populations and effectively managing captive populations. Here we present two case studies of the dietary and ranging behavior of semi-free ranging ring-tailed lemurs (Lemur catta; two groups) and red ruffed lemurs (Varecia rubra; two groups) at the Myakka City Lemur Reserve managed by the Lemur Conservation Foundation. We found that ring-tailed lemurs spent 64.5% of their time resting and 13.4% foraging and feeding. The most important food types for ring-tailed lemurs were mature leaves (55.9%) and detritus (12.6%); however, they consumed nine other food types, including living animals (0.7%). Ring-tailed lemurs consumed 14 plant species, 9 of which have not previously been reported. Home ranges for the two ring-tailed lemur groups were 0.18 ha and 0.20 ha, representing 9.7% and 11.4% of their forested enclosures. Ring-tailed lemurs foraged primarily within one meter from the ground. Red ruffed lemurs spent 44.9% resting and 29.6% foraging and feeding. The most important food types for red ruffed lemurs were young leaves (32.9%), mature leaves (22.0%), flower buds (15.7%), and unripe fruit (11.9%) with only three other food types consumed. Red ruffed lemurs consumed 43 different species, all of which have not been previously reported. Home ranges for the two red ruffed lemur groups were 0.83 ha and 0.87 ha representing 40.8% and 55.9% of their forested enclosures. Red ruffed lemurs also foraged primarily within one meter from the ground. This is one of very few published studies on semi-free ranging ring-tailed lemurs outside Madagascar and the first dietary study on semi-free ranging red ruffed lemurs outside Madagascar. We hope that these results can be used to inform management practices among captive lemur populations, other primates, and other taxa living in novel environments.

Diet and nutrition are critical factors influencing energetics and health. Laboratory studies show that organisms adjust to changes in nutrient intake through flexible metabolic responses such as fuel switching. While the physiological effects of nutrient balance in humans have been studied, data from closely related species living in nature are lacking. We integrate macronutrient regulation and metabolic flexibility to elucidate how wild orangutans (
Pongo pygmaeus wurmbii
) are buffered against natural fluctuations in nutritional resources. We found that these orangutans regulate protein and regularly switch between exogenous and endogenous nutritional substrates as preferred food resource availability declines. When total caloric, lipid, and carbohydrate intake declined during episodes of fruit scarcity, orangutans drew on fat and endogenous amino acids for energy. This strategy is beneficial only in the context of alternating periods of fruit scarcity and abundance. We discuss our findings in relation to the current global obesity pandemic, which has arisen with transitions in human diets toward low-cost, energy-dense, protein-dilute foods.
Orangutans have evolved behavioral and metabolic flexibility to cope with a feast-and-famine ecology.

Objectives: Temporal variation in food availability can pose nutritional challenges to primates. Characterizing the nutritional content of the non-preferred foods that primates switch to, termed fallback foods, is useful for identifying the nutritional challenges of lean periods, the nutritional limits of what primates can subsist on, and physiological adaptations. We explored the temporal patterning and the nutritional contribution of food items for Bornean orangutans (Pongo pygmaeus wurmbii) at Tuanan, Indonesia, with particular attention to the liana, Bowringia callicarpa. Materials and Methods: We quantified the nutritional contribution of food items to the diet of wild orangutans over 18 years. We modeled the relationship between preferred food availability and the nutritional contribution of Bowringia. Results: Bowringia played an outsize role in the feeding time and nutritional intake of orangutans. It can be characterized as a fallback food because it is increasingly consumed when preferred tree fruits are less available. Its immature leaves are particularly important as the greatest source of protein and energy. However, the nonprotein energy-to-protein ratio of Bowringia is extremely low, and overreliance on it would bring orangutans away from their estimated nutritional intake target. Discussion: Despite its high energy and protein content, Bowringia is a nutritionally imbalanced food. Fallback food quality should thus be evaluated based on the ability to bring an animal toward its nutritional goal rather than nutrient density. We propose that orangutans are preadapted to falling back on protein-dense foods and the great abundance of Bowringia has contributed to the high population density of orangutans at Tuanan.

The spatial and temporal variation in food abundance has strong effects on wildlife feeding and nutrition. This variation is exemplified by the peatland forests of Central Kalimantan, which are characterized by unpredictable fruiting fluctuations, relatively low levels of fruit availability, and low fruit periods (<3% of trees fruiting) that can last nearly a year. Challenged by these environments, large, arboreal frugivores like orangutans must periodically rely on non-preferred, lower-quality foods to meet their nutritional needs. We examined variation in nutrient intake among age-sex classes and seasons over a 7-year period at the Tuanan Orangutan Research Station in Central Kalimantan. We conducted 2,316 full-day focal follows on 62 habituated orangutans (Pongo pygmaeus wurmbii). We found differences in total energy and macronutrient intake across age-sex classes, controlling for metabolic body mass. Intake of both total energy and macronutrients varied with fruit availability, and preference of dietary items increased with their nutritional quality. Foraging-related variables, such as day journey length, travel time, and feeding time, also varied among age-sex classes and with fruit availability. Our results add to the growing body of literature suggesting that great variation in foraging strategies exists among species, populations, and age-sex classes and in response to periods of resource scarcity.

Bottom-up regulatory factors have been proposed to exert a strong influence on mammalian population density. Studies relating habitat quality to population density have typically made comparisons among distant species or communities without considering variation in food quality among localities. We compared dietary nutritional quality of two Bornean orangutan populations with differing population densities in peatland habitats, Tuanan and Sabangau, separated by 63 km. We hypothesized that because Tuanan is alluvial, the plant species included in the orangutan diet would be of higher nutritional quality compared to Sabangau, resulting in higher daily caloric intake in Tuanan. We also predicted that forest productivity would be greater in Tuanan compared to Sabangau. In support of these hypotheses, the overall quality of the diet and the quality of matched dietary items were higher in Tuanan, resulting in higher daily caloric intake compared to Sabangau. These differences in dietary nutritional quality may provide insights into why orangutan population density is almost two times greater in Tuanan compared to Sabangau, in agreement with a potentially important influence of diet quality on primate population density.