Demographic Features of Alouatta pigra Populations in Extensive and Fragmented Forests

Abstract

Until now, little information was known about demographic features of the regionally endemic black howler populations living in large tracks of tropical forests. Here, we report results from population surveys conducted in eight extensive forests sites (>8.5 km2) in Mexico and Guatemala. We also surveyed the black howler population in the fragmented landscape bordering two of the extensive forest reserves. Based on the 120 troops encountered in the extensive forest sites, mean troop size was 6.57 (SE = 1.20) individuals (range 2–12 individuals). Troops had most commonly a multimale-multifemale social structure, with two adult males and two adult females being the most common. Population densities ranged from 12.7 to 44.1 individuals/km2. Mean troop size and composition were not correlated to population densities. For the two fragmented landscapes bordering the extensive forests, mean densities in forest fragments were, on average, five times higher than in extensive forests. Mean troop composition was not significantly different between forest fragments and extensive forests, but data suggest a tendency of fewer males in troops living in forest fragments. Long-termmonitoring in extensive forests is necessary to document variability in population dynamics and to make adequate assessments of the consequences of fragmentation on demography, behavior, and life history of A. pigra.