Group Structure and Dynamics in Black Howlers (Alouatta pigra): A 7-year Perspective

摘要

The long-term monitoring of group structure and dynamics is critical to the study of primate ecology and evolutionary processes, as well as to understand the responses of individuals to changes in their environments. We monitored individually recognized black howlers (Alouatta pigra) belonging to 11 groups for 7 yr in different habitats and landscapes in Campeche (Mexico). Our aims were 1) to describe group structure and dynamics; 2) to determine whether group structure and dynamics changed significantly over time; and 3) to evaluate which habitat and landscape-scale attributes best predicted variation among groups in structure and dynamics. Each year we surveyed the groups twice in each climatic season (wet and dry season), resulting in a total of 10,083 sampling days. Although group size increased over time, mostly as a result of moderate to high infant survival rates and increases in the number of juveniles in groups, other demographic parameters, such as the number of adults and infants per group, were stable. We observed no group takeovers involving two or more males and infrequent takeovers by solitary males; frequent disappearances of individuals of both sexes from their natal groups around the age of sexual maturation, suggesting a bisexual dispersal pattern; concentration of births in the wet season; male-biased sex ratios at birth but female-biased immature survival. Group structure and dynamics were affected by both habitat and landscape-scale attributes, but factors acting at the habitat scale had an overall higher impact on demographics. Besides reporting new life history and demographic data for this species, the results from this study suggest that black howlers may be more sensitive to habitat disturbance than previously reported.