Ecological separation of two sympatric species of Microcebus spp. E. Geoffroy, 1812 in southern Madagascar

Abstract

Classical hypotheses suggest that two species cannot coexist if they share the same ecological niche. Observations of a number species sharing the same habitat suggest that species can coexist if they utilize different resources, adapt differently to environmental conditions, or differ in size.

In this thesis, I use two sympatric species of mouse lemurs, the reddish-gray mouse lemur (Microcebus griseorufus) and the gray mouse lemur (M. murinus), to study their distribution along a gradient of ecosystems and to determine the mechanisms that allow these two species to coexist despite seemingly identical ecological requirements. These two species are morphologically very similar and represent sister species, i.e., they are the least likely primate species to coexist due to their phylogenetic similarity. They co-occur in the dry spiny forest in southern Madagascar.

This study was carried out from September 2006 to June 2009 at Andohahela National Park in the extreme south-east of Madagascar. This area provides an ideal opportunity to investigate the various patterns and evolutionary constraints along a continuous environmental gradient ranging from evergreen humid rainforest to dry spiny forest.

The aims of this study were (1) to investigate the environmental conditions that are associated with the distribution of the two Microcebus species and their hybrids; (2) to study the possible mechanisms that allow the coexistence of these sympatric congeneric species (M. murinus and M. griseorufus) by investigating the potential separation with respect to food composition. This study is based on stable isotopes as an indirect measure of the trophic level of the consumer and its prey; (3) to describe microhabitat utilization of both species.

The results showed that Microcebus murinus and M. griseorufus are clearly associated with specific habitat types that are related to the different abiotic and biotic environmental conditions. Along the vegetation gradient of Andohahela National Park, M. griseorufus is associated with dry conditions, while M. murinus is associated with more mesic conditions. Co-occurrence of these congeneric species appears to be allowed through microhabitat differentiation and different degrees of insectivory, during the lean season, M. griseorufus eat more insects than M. murinus. Microcebus murinus was found in microhabitats with larger trees than average while M. griseorufus utilized microhabitats with smaller trees than average.