Among mammals, the order Primates is exceptional in having a high taxonomic richness in which the taxa are arboreal, semiterrestrial, or terrestrial. Although habitual terrestriality is pervasive among the apes and African and Asian monkeys (catarrhines), it is largely absent among monkeys of the Americas (platyrrhines), as well as galagos, lemurs, and lorises (strepsirrhines), which are mostly arboreal. Numerous ecological drivers and species-specific factors are suggested to set the conditions for an evolutionary shift from arboreality to terrestriality, and current environmental conditions may provide analogous scenarios to those transitional periods. Therefore, we investigated predominantly arboreal, diurnal primate genera from the Americas and Madagascar that lack fully terrestrial taxa, to determine whether ecological drivers (habitat canopy cover, predation risk, maximum temperature, precipitation, primate species richness, human population density, and distance to roads) or species-specific traits (body mass, group size, and degree of frugivory) associate with increased terrestriality. We collated 150,961 observation hours across 2,227 months from 47 species at 20 sites in Madagascar and 48 sites in the Americas. Multiple factors were associated with ground use in these otherwise arboreal species, including increased temperature, a decrease in canopy cover, a dietary shift away from frugivory, and larger group size. These factors mostly explain intraspecific differences in terrestriality. As humanity modifies habitats and causes climate change, our results suggest that species already inhabiting hot, sparsely canopied sites, and exhibiting more generalized diets, are more likely to shift toward greater ground use.

Habitat disturbance disrupts the ecological interactions of mammals, leading to negative consequences for biodiversity. In particular, it is suggested that parasite-host interactions are affected in tropical ecosystems, with parasite diversity reduced as environmental perturbations take place. In this study, we examined whether the disruption of tropical forests affects the presence of parasites in a population of endangered black howler monkeys (Alouatta pigra) that inhabits a highly fragmented landscape in Balancán, Tabasco, Mexico. Our working hypothesis was that increased forest perturbation would negatively affect the incidence of parasitic infections (parasite presence and richness) in black howler monkeys. We conducted a parasitological study and collected stool samples from 65 adult individuals living in 30 forest fragments across a disturbance gradient. We recovered parasite eggs from stool samples using flotation and sedimentation techniques. We selected fragment size and distance from each forest fragment to the nearest village as measures of forest perturbation. We analyzed the effects of forest perturbation on parasite presence and richness using generalized linear models. Other driving factors such as seasonality, host density, and sex were also considered in the models. Gastrointestinal parasite infection was positively related to distance between forest fragments and the nearest human settlement (β = 0.55 ± SE 0.28, z = 2.0, P = 0.05). No effects of fragment size or any other variable considered in the model on the presence of parasite infection were observed. Parasite richness was not affected by any of the measures of forest perturbation, nor by any other variables considered in the analysis. Our findings suggest that an increase in forest perturbation may negatively affect the probability of parasite infection in black howler monkeys, as individuals living in close proximity to human settlements showed a lower presence of parasites. We proposed that the low parasite infection rates recorded in this monkey population reflect synergistic effects associated with both the alteration of the parasite-primate network, as well as the low resilience of parasites to thrive in a disrupted ecosystem.

El presente estudio utilizó datos de precipitación y temperatura de 1960-2015 y de Modelos de Circulación Global (MCG) CNRMCM5 y HADGEM2_ES, proyectados a 2045-2069 y 2075-2099; bajo dos rutas de concentraciones de emisiones de gases de efecto invernadero (RCP); 4.5 (constantes) y 8.5 (altas). El objetivo fue probar la hipótesis de que la RBPC se convertiría en un sitio altamente expuesto al aumento en temperatura promedio anual e inundable por el incremento del nivel del mar. Los registros de precipitación y temperatura se descargaron de seis estaciones meteorológicas y capas climáticas de MCG para 2045-2069 y 2075-2099 (RCP 4.5 y 8.5) a una resolución de 1 km2. Las pruebas estadísticas utilizadas en los datos permitieron detectar tendencias de aumento (p < 0.05) a través del tiempo. Debido a la incertidumbre de los escenarios climáticos a futuro, se probaron y analizaron cuatro escenarios. Los resultados indican una tendencia de aumento significativo en temperatura promedio anual de 0.34 a 0.82 ◦C para 1960-2015. Los escenarios climáticos futuros proyectaron que la RBPC sería más cálida, seca e inundada por el incremento del nivel del mar de 13 a 33 cm, lo que propiciará en la formación de un delta costero, abarcando entre 49.3 a 49.5% de la RBPC durante 2045-2099. Conforme con los análisis climáticos, la RBPC podría ser un área altamente expuesta al calentamiento global e incremento del nivel del mar. Este último ocasionaría cambios biogeoquímicos importantes en los cuerpos de agua dulce del área.