Locomotor ecology of Lepilemur edwardsi and Avahi occidentalis

A well-known principle holds that where food supply is limited, two sympatric species with the same diet, morphology, and behavior will compete, leading to exclusion of one species or differentiation of their ecological niches. Avahi occidentalis and Lepilemur edwardsi are two saltatory, nocturnal folivorous lemurs of similar body size which live sympatrically over much of their range and may often be seen feeding in the same trees. We report a study of their locomotor behavior, carried out in order to determine to what extent locomotion might contribute to niche separation. Avahi lives at a higher level in the forest and is the more committed leaper, with a much larger home range and nightly travel distance, while Lepilemur climbs more and has a very small nightly travel distance. Avahi uses small, low-angled supports more often, while Lepilemur makes more use of large, high-angled supports (however, neither species uses vertical supports at a frequency greater than the availability of such supports in the forest stratum in which they live). Both species tend to land on larger-diameter supports on longer leaps, but Avahi also takes off from larger-diameter supports in longer leaps, reducing loss of energy to the substrate during takeoff. We suggest that the differences in locomotion and ranging behavior between them are consistent with niche differentiation on the basis of food quality, Avahi investing more energy in harvesting better quality but more patchy food, Lepilemur minimizing expenditure in harvesting a less selective, quantitatively poorer diet.