Quality and overlap of individual core areas are related to group tenure in female spider monkeys.

In species with a high degree of fission-fusion dynamics group members may differ in the use of the group home range to reduce food competition. Such differential use may result in distinct individual core areas. We studied core area quality and overlap among 21 female spider monkeys belonging to the same group over a period of 4 years. Core areas ranged between 62 and 161 ha with a mean overlap of 56% between any given two females. Only a small portion (mean = 3 ha) of each individual core area was used exclusively. No single part of the home range was used as core area by all females, and only an area of less than 1 ha was used as part of the core area by 20 of the 21 females. The time a female spent in the group (i.e., group tenure) was associated with characteristics of the core areas: the longer the group tenure, the better the quality of her core area. In addition, the longer the time two females spent together in the same group, the larger the overlap between their individual core areas. As this result was obtained while controlling for the time two females spent together in the same subgroup, females may reduce direct competition by using the same resource at different times. In sum, spider monkey females' group tenure plays a central role in the quality and overlapping patterns of their individual core areas.

Variability in core areas of spider monkeys (Ateles geoffroyi) in a tropical dry forest in Costa Rica.

Core areas are highly used parts of the home range on which the survival of solitary or group-living animals depends. We investigated the home range and core area size and area fidelity of a spider monkey community in a tropical dry forest over a 4-year period. Home ranges overlapped extensively across years, subgroup sizes, and seasons. In contrast, spider monkeys used core areas that varied in size and location across the study years, subgroup sizes, and seasons. These shifts in core areas suggest that the understanding of core areas, and thus the spatial requirements, of a species in a particular habitat may be limited if based on short-term studies. In this respect, our findings emphasize the importance of long-term studies of the spatial ecology of any species in a particular habitat. Our study also shows that the yearly home range basically includes all the core areas from different years, seasons, and subgroup sizes (i.e., the super-core area). This is conceptually important for territorial species, such as spider monkeys, which defend a stable home range as it contains not only the current, but also the future core areas.

Demography, life history and migrations in a Mexican mantled howler group in a rainforest fragment.

This paper represents the results of a long-term study (1996-2003) on the demographic changes over time of a Mexican mantled howler (Alouatta palliata mexicana) group in a rainforest fragment (40 ha) in Los Tuxtlas, Mexico, with a follow-up census 3 years later (2006). In addition to demographic and life history parameters, we describe six dispersal events. Our results suggest that this group has been expanding during the study period, growing from six to 12 individuals, with an annual average intrinsic growth rate of 0.07, an infant survivorship of 67%, and an average immature to female ratio of 0.90. This increase in size is probably related to the high food availability in their home range. However, fragment isolation may be negatively affecting the dispersal patterns typical of the species, which could result in a loss of genetic variability over time.

Foraging habits of Alouatta palliata mexicana in three forest fragments.

The activity patterns and diet of howler monkeys (Alouatta palliata mexicana) were studied in 3 forest fragments in south-eastern Mexico: Playa Escondida (PLA), Agaltepec Island (AGA) and Arroyo Liza (LIZ). Intersite differences offered the opportunity to investigate the foraging adaptations of howler monkeys in response to population and habitat size. In the largest fragment (PLA), the howlers' diet was based on high-quality items (fruit and young leaves). In AGA, where the density of howlers was the highest, their diet was mostly folivorous with a marked exploitation of uncommon food items such as vines, lianas, shrubs and herbs. The dietary differences in AGA were accompanied by more time spent travelling and less time spent resting. Although LIZ was the smallest fragment and had a high howler density, the small group size and the use of energy-minimizing strategies (less time spent travelling and more time spent resting) probably allowed howlers to maintain a frugivorous diet.

Biogeographical and floristic predictors of the presence and abundance of mantled howlers (Alouatta palliata mexicana) in rainforest fragments at Los Tuxtlas, Mexico.

This research focuses on identifying the principal habitat characteristics that influence the presence and abundance of mantled howlers in forest fragments. We provide information on the demography of several fragmented Alouatta palliata mexicana subpopulations at Los Tuxtlas, Mexico, and relate this to the biogeographical and floristic characteristics of the forest fragments inhabited. The most important habitat characteristics related to the presence and abundance of howlers in the fragments were fragment size and floristic diversity. On the other hand, some evidence suggests that given the conditions under which howlers in our study area live (i.e., small and degraded fragments with high densities), secondary vegetation may be beneficial for the survival of the howlers. Finally, we discuss the possibility that the very low immature-to-female ratio (IFR) in the groups, and the lack of juveniles found in many of the study groups may be due to high mortality rates in immatures. A reduction in food availability because of the high population densities of these groups may be responsible for this process.

Interspecific interaction and predator avoidance behavior in response to tayra (Eira barbara) by mantled howler monkeys (Alouatta palliata).

This paper reports the response of one howler monkey group (Alouatta palliata) to a group of potential predators, the tayra (Eira barbara). The apparently successful predator avoidance behavior of the monkeys was recorded in detail. We observed a group of four adult tayras moving around the Alouatta group displaying a species-typical aggressive behavioral pattern. The two adult females of the howler group successfully chased the tayras away by repeatedly moving closer to the mustelids and even following them until the predators moved off.