Population Dynamics of Nocturnal Lemurs in Littoral Forest Fragments: The Importance of Long-Term Monitoring

Habitat loss and fragmentation pose a significant threat to many primate species worldwide, yet community-level responses are complex and nuanced. Despite repeated calls from primatologists and the wider conservation community to increase monitoring initiatives that assess long-term population dynamics, such studies remain rare. Here we summarize results from a longitudinal study set in the littoral forests of southeast Madagascar. Littoral forests are a useful model for monitoring lemur population dynamics, as they are relatively well studied and their highly fragmented nature enables the effect of forest size and anthropogenic impacts to be examined. This study focuses on three Endangered nocturnal lemur species—Avahi meridionalis, Cheirogaleus thomasi, and Microcebus tanosi—across three forest fragments of different size and with different usage histories. Between 2011 and 2018, we walked 285 km of line transect and recorded 1968 lemur observations. Based on distance sampling analysis our results indicate that nocturnal lemurs respond to forest patch size and to levels of forest degradation in species-specific ways. The largest species, A. meridionalis, declined in density and encounter rate over time across the three study forests. C. thomasi populations appeared stable in all three fragments, with densities increasing in the most degraded forest. M. tanosi encounter rates were extremely low across all study fragments but were lowest in the most heavily degraded forest fragment. Our results emphasize the importance of localized pressures and species-specific responses on population dynamics. Monitoring population trends can provide an early warning signal of species loss and species-specific responses can inform crucial intervention strategies.