Browsing by Subject "RANOMAFANA-NATIONAL-PARK"

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    Estimating the population size of lemurs based on their mutualistic food trees
    (Journal of Biogeography, 2018-11-01) Herrera, JP; Borgerson, C; Tongasoa, L; Andriamahazoarivosoa, P; Rasolofoniaina, BJR; Rakotondrafarasata, ER; Randrianasolo, JLRR; Johnson, SE; Wright, PC; Golden, CD
    Aim: Species’ distributions and abundances are primarily determined by the suitability of environmental conditions, including climate and interactions with sympatric species, but also increasingly by human activities. Modelling tools can help in assessing the extinction risk of affected species. By combining species distribution modelling of abiotic and biotic niches with population size modelling, we estimated the abundance of 19 lemur taxa in three regions, especially focusing on 10 species that are considered Endangered or Critically Endangered. Location: Madagascar. Taxa: Lemurs (Primates) and angiosperm trees. Methods: We used climate data, field samples, and published occurrence data on trees to construct species distribution models (SDM) for lemur food tree species. We then inferred the SDMs for lemurs based on the probability of occurrence of their food trees as well as climate. Finally, we used tree SDMs, topography, distance to the forest edge, and field estimates of lemur population density to predict lemur abundance in general linear models. Results: The SDMs of lemur food trees were stronger predictors of the occurrence of lemurs than climate. The predicted probability of presence of food trees, slope, elevation, and distance from the forest edge were significant correlates of lemur density. We found that sixteen species had minimum estimated abundances greater than 10,000 individuals over >1,000km2. Three lemur species are especially threatened, with less than 2,500 individuals predicted for Cheirogaleus sibreei, and heavy hunting pressure for the relatively small populations of Indri indri and Hapalemur occidentalis. Main conclusions: Biotic interactors were important variables in SDMs for lemurs, allowing refined estimates of ranges and abundances. This paper provides an analytical workflow that can be applied to other taxonomic groups to substantiate estimates of species’ vulnerability to extinction.
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    Morphometric signals of population decline in diademed sifakas occupying degraded rainforest habitat in Madagascar.
    (Scientific reports, 2019-06-19) Irwin, Mitchell T; Samonds, Karen E; Raharison, Jean-Luc; Junge, Randall E; Mahefarisoa, Karine Lalaina; Rasambainarivo, Fidisoa; Godfrey, Laurie R; Glander, Kenneth E
    Anthropogenic habitat change can have varied impacts on primates, including both negative and positive outcomes. Even when behavioural shifts are seen, they may reflect decreased health, or simply behavioural flexibility; understanding this distinction is important for conservation efforts. This study examines habitat-related variation in adult and immature morphometrics among diademed sifakas (Propithecus diadema). We collected morphometric data from sifakas at Tsinjoarivo, Madagascar (19 years, 188 captures, 113 individuals). Captures spanned 12 groups, five within continuous forest ("CONT"), and seven in degraded fragments ("FRAG") where sifakas have lower nutritional intakes. Few consistent differences were found between CONT and FRAG groups. However, using home range quality as a covariate rather than a CONT/FRAG dichotomy revealed a threshold: the two FRAG groups in the lowest-quality habitat showed low adult mass and condition (wasting), and low immature mass and length (stunting). Though less-disturbed fragments apparently provide viable habitat, we suggest the sifakas in the most challenging habitats cannot evolve fast enough to keep up with such rapid habitat change. We suggest other long-lived organisms will show similar morphometric "warning signs" (wasting in adults, stunting in immatures); selected morphometric variables can thus be useful at gauging vulnerability of populations in the face of anthropogenic change.