Lemur Distribution in Relation to Treefall Canopy Gaps in Masoala National Park, Northeast Madagascar.

Madagascar is a biodiversity hotspot facing increasing anthropogenic pressures, with 95% of lemur species threatened with extinction. In addition to habitat loss and hunting, cyclones create treefall gaps with unknown effects on arboreal species. We examined the effect of Cyclone Eliakim, which struck Masoala National Park in March 2018 with sustained wind speeds reaching 151 km/h. We assessed whether lemur densities and their microhabitat niches changed in relation to the cyclone, and whether their distributions were related to treefall gaps. We conducted 110.42 km of transect walks for diurnal and 86.93 km for nocturnal lemurs between 2017 and 2022 in Andranobe, Masoala National Park, a region regularly hit by cyclones. Microhabitat data were recorded for each observation, and distance to the nearest canopy gap was used as a measure of association with treefall gaps. Densities of Varecia rubra, Eulemur albifrons, Avahi mooreorum, Lepilemur scottorum, and Microcebus sp. did not decline after the cyclone. Species niche separation was strongest directly after the cyclone (suggesting intensified competition over limited resources) and relaxed progressively as the forest recovered. Gap size increased after the cyclone and decreased by 59.9% 4.5 years later, indicating progressive canopy closure. Large diurnal lemurs were positively associated with gaps > 150 m2, likely reflecting increased food availability in sun-exposed areas. Small nocturnal lemurs were positively associated with small gaps (< 150 m2) but avoided larger gaps, possibly due to aerial predator risk. These data aid our understanding of species interactions and ecosystem dynamics under climate-driven habitat change.