Behavioral and physiological responses to fruit availability of spider monkeys ranging in a small forest fragment

Abstract

Numerous animal species currently experience habitat loss and fragmentation. This might result in behavioral and dietary adjustments, especially because fruit availability is frequently reduced in fragments. Food scarcity can result in elevated physiological stress levels, and chronic stress often has detrimental effects on individuals. Some animal species exhibit a high degree of fission–fusion dynamics, and theory predicts that these species reduce intragroup feeding competition by modifying their subgroup size according to resource availability. Until now, however, there have been few studies on how species with such fission–fission dynamics adjust their grouping patterns and social behavior in small fragments or on how food availability influences their stress levels. We collected data on fruit availability, feeding behavior, stress hormone levels (measured through fecal glucocorticoid metabolites (FGCM)), subgroup size, and aggression for two groups of brown spider monkeys (Ateles hybridus) in a small forest fragment in Colombia and examined whether fruit availability influences these variables. Contrary to our predictions, spider monkeys ranged in smaller subgroups, had higher FGCM levels and higher aggression rates when fruit availability was high compared to when it was low. The atypical grouping pattern of the study groups seems to be less effective at mitigating contest competition over food resources than more typical fission–fusion patterns. Overall, our findings illustrate that the relationship between resource availability, grouping patterns, aggression rates, and stress levels can be more complex than assumed thus far. Additional studies are needed to investigate the long-term consequences on the health and persistence of spider monkeys in fragmented habitats.

Responses to social and environmental stress are attenuated by strong male bonds in wild macaques

“…Several studies, however, failed to replicate the negative effect of aggression received on an individual's physiological stress level (55,(60)(61)(62)(63). Our results suggest that in these latter studies interaction effects in the social buffering mechanism may have blurred the patterns observed and may explain ambiguities between some studies and species.…”

Brown spider monkeys ( Ateles hybridus ): a model for differentiating the role of social networks and physical contact on parasite transmission dynamics

“…Changes in subgroup composition were recorded whenever one or more individuals joined ('fused') or left ('fissioned') the subgroup containing the focal animal. We considered individuals as belonging to the same subgroup when they were at a distance of less than or equal to 50 m from at least one other subgroup member following a chain rule [53,56]. On a daily basis, multiple observers (2-5) followed one focal individual each, thereby increasing the probability of noting 'fission' and 'fusion' events.…”

“…For this study, we collected data on one study group (SJ-1), which during the study period consisted of three to four adult males, five adult females, one subadult female, one to three subadult males, zero to two juvenile males, three to four juvenile females, one infant male and one infant female (total ¼ 14-16). The forest fragment was occupied by a second group of brown spider monkeys, but intergroup encounters between these two groups were rare [53], however, and almost never included physical contact. Thus, we assumed that between-group parasite transmission rates were very low or non-existent.…”

Unraveling the disease consequences and mechanisms of modular structure in animal social networks

“…In contrast to network fragmentation and subgroup cohesion, we found variation in subgroup sizes to have a weak negative effect on network modularity. Fluid subgroup sizes are common in many social species (e.g., in spotted hyenas, elks, chimpanzees, bottlenose dolphins, and African lions) and can be brought about by changes in resource availability, intragroup aggression, demographic factors (such as sex ratio), dominance hierarchy, and female reproductive state (13,15,16).…”