This analysis is based on a census of the primate populations of the southeastern part of the Los Tuxtlas Biosphere Reserve. The demographic data obtained in 2008 were compared to those formerly reported in 1985, to identify the primate population trends in this region. A total of 37 individuals of Alouatta palliata mexicana and 68 individuals of Ateles geoffroyi vellerosus were found in 12 fragments. The size of the total primate population in this site is similar to that reported at the end of the 80's. Nonetheless, the ecological density was higher and a wane in the adult females and immature proportions within primate groups was observed. This could be considered as the beginning of demographic decline processes inside primate population in this region, which could be a consequence of a decrease in habitat quality and quantity. Improving the connectivity between forest fragments was suggested as a conservation measure within a strategy that takes into account the complexity of land dynamics in the region.

In fragmented habitats, an increase in the proportion of available forest edge has been positively correlated to parasite richness. We evaluated how the presence of forest edge may affect parasite-host dynamics in a population of wild owl monkeys (Aotus azarai azarai) in an unlogged gallery forest in Formosa, Argentina. We collected 53 fecal samples from groups inhabiting edge territories (n = 7 groups, 33 samples) and groups inhabiting the interior of the forest (n = 3 groups, 15 samples). We compared the number of parasite species (richness) found between the two types of groups, as well as the frequency of samples with multiple infections (more than one parasite species in the sample) and the distribution of helminths on the forest floor between habitat types. The number of parasite species, the proportion of samples with multiple infections and the helminth distribution were not significantly different across the two habitat types.

The conservation status of the Mexican howler monkey in core zone III of Los Tuxtlas Biosphere Reserve, Veracruz, Mexico, is uncertain. Here, we provide the first set of demographic data of Alouatta palliata mexicana in the southern sector of the core zone III by using two different methods: line transect and sweep census. A total of twenty-six individuals divided in 6 groups were registered inhabiting the continuous forest, with a mean group size of 4 (± 0.5) individuals and a range of 3 to 6 individuals. The density of the animals for the study site was 0.04 howler monkeys/ha. Conversely, no individuals were found in any of the fragments surveyed within the buffer zone. Overall, field research showed a much lower density than was expected, suggesting historical and/or contemporary factors may be directly and/or indirectly affecting the persistence of the howlers in the area. New studies focused on the environmental changes caused by natural or anthropogenic factors will be of great aid in future management interventions and viability assessments of the population.