Master of Science (MS)
Central America has two howling monkey species: the widespread mantled howling monkey (Alouatta palliata) and the endemic and endangered black howling monkey (A. pigra) limited to southeastern Mexico, northern Guatemala and Belize. Studies that verify the distribution of these species are needed, especially in their contact zones where sympatry is reported. Their evolutionary history remains controversial. My study examines their distribution at a local scale in a potential contact zone in eastern Guatemala through direct observations and interviews and at a regional scale across the entire isthmus using data from museum specimen localities, study sites, historic records and field surveys. Using GIS I analyzed the distributions against geographic and ecological features to infer current barriers between both species and explore the possibility of their role in the initial speciation. I found no evidence for current sympatry in eastern Guatemala; instead parapatry is maintained by a riverine barrier and by ecological adaptation, as only A. pigra occurs in the cold montane habitats further inland. My study reveals broader elevational and vegetational tolerances by A. pigra than previously reported. My results suggest differences in elevation and cold tolerances by the two species which I consider an important ecological barrier separating them at present. I identified the highland massif of northern Central America and their associated coniferous and subalpine vegetation as a geographic barrier. In contrast to other studies, I propose that both species ranges are not adjacent throughout, but separated by these mountains and only coming into contact in a broad sympatry zone in the lowlands north of the highland massif in Mexico and in the narrow parapatry zone in Guatemala. I present an alternative biogeographic hypothesis that proposes an initial split by the northern Central American highland massif during cold periods that resulted in the isolation of the A. pigra lineage in the Yucatan peninsula and in the further divergence in cold tolerance.
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Baumgarten, Amrei, "Distribution and biogeography of Central American howling monkeys (Alouatta pigra and A. palliata)" (2006). LSU Master's Theses. 2417.
G. Bruce Williamson