Estimating Encounter Rates and Densities of Three Lemur Species in Northeastern Madagascar
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Primate populations, including Madagascar’s lemurs, are threatened worldwide and conservationists need accurate population estimates to develop targeted conservation plans. We sought to fill knowledge gaps for three lemur taxa —white-fronted brown lemur (Eulemur albifrons); eastern woolly lemur (Avahi laniger); and Allocebus/Microcebus, a category combining observations of hairy-eared dwarf lemurs (Allocebus trichotis) and mouse lemurs (Microcebus spp.)— in northeastern Madagascar by estimating their density, examining how their encounter rates and densities vary across three different forest types, and monitoring trends in encounter rates and densities at resurveyed sites, using data from surveys at six forest sites over a 4-year period (2010–2013). Landscape density for white-fronted brown lemur, eastern woolly lemur, and Allocebus/Microcebus was 21.5 (SE 3.67), 57.7 (SE 9.17), and 39.1 (SE 9.55) individuals/km2, respectively. There was no difference in density estimates at intact and intermediately degraded forest sites; however, we encountered white-fronted brown lemurs more often in intact forest (1.64 ± SE 0.40 individuals/km) than in intermediately degraded and degraded forest (0.15 ± SE 0.06 and 0.16 ± SE 0.06 individuals/km). In addition, we encountered white-fronted brown lemurs at lower rates in 2013 (0.15 ± SE 0.06 individuals/km) compared to 2010 (0.82 ± SE 0.12 individuals/km) at a resurveyed site. Our findings emphasize that primate researchers must account for variation in how lemur encounter rates and densities differ between intact and degraded forests, and although we observed a decline in white-fronted brown lemur encounter rate at our resurveyed site, we caution that changes in lemur encounter rates may simply reflect lower detection rates rather than lower density. Future research should focus on using conventional distance sampling techniques, which are infrequently used in primate studies, to provide more robust density estimates as a way to accurately assess trends and the effects of anthropogenic pressures on lemur populations.
KeywordsDistance sampling Habitat degradation Primate Rainforest
This research was funded by the National Science Foundation (grant no. DGE 0822220), Sigma Xi, Cleveland Metroparks Zoo, European Association for Zoos and Aquaria, Idea Wild, National Geographic Society-Waitts grant #W96-10, People’s Trust for Endangered Species, Virginia Tech Chapter of Sigma Xi, Virginia Tech, and Wildlife Conservation Society Madagascar Program (WCS-MP). We thank Dean Stauffer and Steig Johnson for all the advice they provided. We thank our Malagasy field assistants B. L. Donah, Marka’Helin, R. Wilson, B. J. R. Rasolofoniaina, E. J. G. Anjaraniaina, Didice, and Augustain; numerous Malagasy collaborators; and our many field volunteers and data entry volunteers. We thank WCS-MP, especially Christopher Holmes, and Antongil Conservation for logistical aid and the Madagascar Government and Madagascar National Parks (MNP) for permitting this project. We appreciate the comments of two anonymous reviewers and the editor-in-chief, which greatly improved this contribution.
This material is based on work supported by the National Science Foundation Graduate Research Fellowship. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors(s) and do not necessarily reflect the views of the National Science Foundation.
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