Intragroup Feeding Competition Research Articles

Examination of increased annual range of a Tana mangabey (Cercocebus galeritus) group

A group of Tana mangabeys (Cercocebus galeritus) has greatly expanded its annual range over three decades: from 17.25 hectares (ha) in 1974 (Homewood [1976] Ph.D. dissertation, University College London) and 18.75 ha in 1988-1989 (Kinnaird [1990a] Ph.D. dissertation, University of Florida) to 46.75 ha in 2000-2001. Utilizing 5-min mapping samples, phenological samples, vegetation data, and statistical and descriptive comparisons with previous data, three hypotheses concerning this range increase were postulated. The hypothesis with the strongest support is an increase in intragroup feeding competition, which was measured by a decrease in fruit availability per hectare and an increase in group size. Fruit biomass estimates of four species individually and of eight species combined showed significant decreases between earlier findings (Kinnaird [1990] Ph.D. dissertation, University of Florida) and this study. Group size decreased from 36 in 1974 to 17 in 1988-1989, and is now 50 individuals. There is no support for the hypotheses that the group is no longer constrained in home range size by neighboring groups or by the extent of forest cover. The changes in group and home range size are also discussed in the context of historical forest loss in the lower Tana River. The ability of the Tana mangabey to increase its home range, especially by traveling through nonforest habitat, is an important aspect of its ecological flexibility in a fragmented and threatened habitat.

Optimal group size and seasonal stress in ring-tailed lemurs (Lemur catta)

Adaptive explanations for social grouping assume that there are fitness consequences associated with group size, and individuals maintain membership in groups of favorable size to maximize fitness. Here I examine fecal cortisol concentrations as a hormonal measure of stress to assess the relative well-being of Lemur catta in groups of different size and in seasons of normal and low tamarind fruit availability. I test the hypotheses that there is an optimal group size at which cortisol is lowest and that optimal group size changes in food-scarce conditions. I collected 799 fecal samples from 87 individuals in seven free-ranging L. catta groups at Berenty Reserve, Madagascar, over a 1-year period (August 1999–July 2000) and determined fecal cortisol concentrations using a radioimmunoassay. Expressing these as residuals from monthly population means to control for temporal fluctuations in cortisol concentration, I calculated mean fecal cortisol levels for each animal in seasons of normal and low tamarind fruit abundance and over the entire year. Overall, females exhibited lowest mean cortisol levels in groups of intermediate size, suggesting that there are benefits to maintaining membership in these groups. Females in groups that were atypically large or small for their habitat type had higher mean cortisol levels than typical groups. Cortisol levels increased in food-scarce conditions for larger groups, suggesting that intergroup competitive advantages do not outweigh intragroup feeding competition at this time. Group size may be optimized for long-term average conditions, and short-term stresses may intermittently alter the costs associated with group size.

Ranging behavior and foraging ecology of lowland woolly monkeys (Lagothrix lagotricha poeppigii) in Yasuní National Park, Ecuador.

In a year-long study, I investigated the ranging behavior of lowland woolly monkeys (Lagothrix lagotricha poeppigii) in a terra firma rainforest in Yasuní National Park, Ecuador, and examined the relationship between ranging, diet, food availability, and food patch use for this population. In Yasuní the total home range sizes for two social groups were 124 and 108 ha, which are much smaller than has been reported previously for Lagothrix elsewhere in its geographic distribution. The mean yearly day range estimates for these same groups were 1,792 m and 1,878 m, which are well within the range of variation previously reported. Ranging behavior was not correlated with the current habitat-wide abundance of ripe fruit, which comprises 76.3% of the yearly diet for this population, but was associated with one measure of likely insect prey abundance and with the availability of immature fruits, a minimal part of the diet. Specifically, one study group moved significantly greater distances during months of high likely insect prey abundance and when immature fruits were abundant. The second study group also traveled farther when likely insect prey abundance was high and when immature fruits were abundant, although the latter relationship only approached significance. This group also devoted significantly more of its daily activity budget to travel during these times. These results indicate that variation in ripe fruit abundance makes no meaningful contribution to explaining variation in ranging behavior for this population of woolly monkeys. Instead, the results raise the possibility that some aspects of the ranging behavior of frugivorous primates may be related to the availability of alternative food sources, such as animal prey, or to monitoring the phenological status of important fruit trees, rather than simply reflecting the degree of intragroup feeding competition.

Effects of group size on ranging patterns in Brachyteles arachnoides hypoxanthus

We collected systematic data on the home range and day ranges of one group of 57–63 muriquis (Brachyteles arachnoides hypoxanthus) at the Estacao Biologica de Caratinga, Minas Gerais, Brazil from September 1998–July 1999, and compared them with similar data collected 15 years ago when the 23–27 individuals in the group traveled together as a cohesive unit. Home range size increased from 168 ha to 309 ha, reflecting an expansion into areas of the forest that were previously unutilized and consistent with the positive relationship predicted between group size and home range size. By contrast, muriquis exhibited remarkable seasonal and interannual stability in their day ranges. Day ranges, which were calculated from 144 days with ≥8 h of observation, averaged 1,313 ± 573 m (median = 1,206 m). Day ranges did not vary with the size of subgroups, defined as independent individuals that traveled with one another out of contact with other group members. Subgroups were significantly larger during the rainy season (mean = 41.8 ± 12.7, median = 46.0 individuals, n = 72) than the dry season (mean = 36.6 ± 13.25, median = 39.5 individuals, n = 72). Subgroups were also larger than the size of the entire group during the previous study, yet their day ranges are indistinguishable. The stability in muriqui day ranges is consistent with predictions for folivorous primates in which other indicators of intragroup feeding competition, such as female dominance relationships, are also absent. We attribute the transition from cohesive to fluid grouping patterns to limits on the number of individuals that can coordinate their movements when they spread out while foraging and suggest that seasonal differences in subgroup sizes without corresponding adjustments in day ranges reflect seasonal differences in the distribution of preferred foods coupled with the effects of reproductive seasonality on muriqui grouping patterns.

Activity and Ranging Patterns of Guerezas in the Kakamega Forest: Intergroup Variation and Implications for Intragroup Feeding Competition

From March 1997 to February 1998, I investigated the activity patterns of 2 groups and the ranging patterns of 5 groups of eastern black-and-white colobus (Colobus guereza), aka guerezas, in the Kakamega Forest, Kenya. Guerezas at Kakamega spent more of their time resting than any other population of colobine monkeys studied to date. In addition, I recorded not one instance of intragroup aggression in 16,710 activity scan samples, providing preliminary evidence that intragroup contest competition may be rare or absent among guerezas at Kakamega. Mean daily path lengths ranged from 450 to 734 m, and home range area ranged from 12 to 20 ha, though home range area may have been underestimated for several of the study groups. Home range overlap was extensive with 49–83% of each group's range overlapped by the ranges of other groups. Despite the high level of home range overlap, the frequently entered areas (quadrats entered on ≥30% of a group's total study days) of any one group were not frequently entered by any other study group. Mean daily path length is not significantly correlated with levels of availability or consumption of any plant part item. Mean daily path length is also not significantly correlated with group size, though the largest group did have the longest mean daily path length. This finding suggests that intragroup scramble competition may have been rare or absent among guerezas at Kakamega except perhaps in the largest group, which was unusually large.

Food supply and chimpanzee (Pan troglodytes schweinfurthii) party size in the Budongo Forest Reserve, Uganda.

A central issue in socioecology is the nature of the relationship between an organism's environment and its social structure. In chimpanzees, the fission-fusion social system is thought to minimize feeding competition for primary dietary components: ephemeral, dispersed patches of ripe fruit. Intragroup feeding competition is thought to force individuals into small parties. Informal observations in the Sonso region of the Budongo forest had suggested that in this habitat, food supply was such that feeding competition was less important in determining grouping patterns than elsewhere. We used data collected on food supply and party sizes over a 4-year period to investigate this suggestion. In accord with theoretical expectation, sizes of foraging parties fluctuated with the size of food patches. However, party sizes showed either negative or no relationship with habitat-wide measures of food abundance. Likewise party sizes showed little relationship to overall measures of food dispersion. For important dietary items, both fruit and leaves had patchy distributions, though the degree of clumping was not strong, and fruit was not more clumped than leaves. Generally, abundant food appeared to be less patchy, and chimpanzees appeared to use more patches as food became more abundant rather than forming larger parties. We suggest that both dispersal and abundance need to be considered when investigating the impact of food supply on grouping patterns, and that the importance of food as a factor in determining chimpanzee grouping patterns declines with increasing levels of abundance.

Constraints on Group Size in Red Colobus and Red-tailed Guenons: Examining the Generality of the Ecological Constraints Model

The ecological constraints model proposes that an increase in group size will increase intragroup feeding competition and thereby constrain group size. Although this model has received wide acceptance, tests of it are based only on a few studies of species that have similar ecological requirements and social organizations, and there are reasons to question the widespread acceptance of the assumptions underpinning it. Via a 2-year study, we explored determinants of group size in species that feed on markedly different types of foods: the folivorous red colobus (Procolobus pennantii) and the frugivorous/insectivorous red-tailed guenon (Cercopithecus ascanius). We established 4 study sites approximately 15 km apart in Kibale National Park, Uganda, to examine the relationship between average group size and food availability. In both species, we quantified interdemic variation in diet, density of food trees, rate of travel, and group size. Red colobus at all sites relied heavily on leaf resources (75.5%–86.9%), but fruit (6.4%–13.9%) and flowers (2.0%–13.9%) were important in some populations. In general, red-tailed guenons fed on fruit (35.7%–59.7%), insects (14.5%–17.6%), and young leaves (12.2%–32.8%), but the amount of time allocated to these foods varied among sites. Average monthly density of trees bearing food items ranged among sites from 45 to 79 trees/ha for red colobus and from 19.6 to 67.3 trees/ha for red-tailed guenons. For both species, rate of travel was similar among sites, with one exception for red colobus. Average red colobus group size varied among sites from 14 to 40 (28 groups counted). Red-tailed guenon group size varied among sites from 11 to 24 (16 groups counted). As predicted by the ecological constraints model, group size increased with food tree density across sites for both species.

Ranging and grouping patterns of a western lowland gorilla group at Bai Hokou, Central African Republic

The ranging and grouping patterns of a gorilla group were studied during 27 months from 1990-1992 at the Bai Hokou study site, Central African Republic. The study group ranged far daily (average = 2.3 km/day) and had a large home range (22.9 km2), relative to mountain gorillas, and ranging patterns differed between years. During 1990-1992, the bimale study group foraged less cohesively and had more flexible grouping patterns than mountain gorillas. The study group sometimes split into two distinct foraging subgroups, each led by a silverback, and these subgroups occasionally slept apart (mean = 950 m apart). Lowland gorillas rely on many of the same fruit resources as sympatric chimpanzees, and under certain demographic situations gorillas, like sympatric chimpanzees, may adapt their foraging group size to reduce intragroup feeding competition. However, the fiber content of the lowland gorilla diet likely relaxes constraints on foraging party size and facilitates group cohesion relative to chimpanzees.

Pair Bonds in Monogamous Apes: a Comparison of the Siamang Hylobates Syndactylus and the White-Handed Gibbon Hylobates Lar

AbstractDescriptions of the social systems of gibbons (Hylobates, Hylobatidae) have typically emphasized generically uniform attributes such as 'monogamy' and 'territoriality'. This has prevented testing of the hypothesis that pair bonds differ in the siamang (Hylobates syndactylus) and the white-handed gibbon (Hylobates lar) (Chivers, 1972). I replace a description of sociality based on mating system and group size/composition with quantitative measurement of social interactions and spatial relations between wild adult males and females in three heterosexual pairs of siamang and two pairs of white-handed gibbons studied for 2.5 years at the Ketambe Research Station (Sumatra, Indonesia). Siamang pair bonds show greater heterosexual cohesion than those of white-handed gibbon as reflected in higher rates of affinitive interactions such as close proximity, relaxed physical contact, embraces, and communal use of sleep trees. Although males are more responsible than females for the maintenance of close proximity in both species, sex differences in intra-pair allogrooming suggest divergent mechanisms maintaining pair bonds in the two species. In white-handed gibbons, the female rarely initiates grooming and grooms her mate significantly less than he grooms her, partly because she solicits grooming from him at higher rates while simultaneously ignoring more of his 'presents' for grooming. In siamang, the contributions of the sexes to grooming are more equivalent and reciprocal. Taken together, these results suggest that investment of the sexes in maintaining the pair bond is more asymmetrical in white-handed gibbons (i.e. males contribute relatively more than females) and more mutual in siamang. Although mate guarding may have been the selective force behind the origin of pair bonds in both species, greater intra-group feeding competition in the gibbon and substantial paternal care in the siamang may account for the evolution of more reciprocal and stronger pair bonds in the latter. Future research on more groups is necessary to clarify the proposed species differences in light of existing intraspecific variation in social behavior.

Food Competition and Foraging Party Size in the Black Spider Monkey (Ateles Paniscus Chamek)

AbstractIn Ateles, individuals forage for fruit in subgroups of unstable membership. The size and composition of these foraging parties are highly variable. Data from my long-term field study of a population of black spider monkeys in Peru show a strong positive correlation between the average size of these parties and the number and size of trees currently producing fruit in the environment. This correlation appears to be driven by intragroup feeding competition, since individuals in larger parties showed substantially lowered feeding efficiencies, as measured by increased daily ranges and decreased time spent feeding. Patch size and patch density, which jointly determine fruit abundance, interact to determine foraging party size, apparently by the following mechanism. The number of spider monkeys that can feed within a particular patch is limited by the size of that patch. When patches are close together (i. e. high patch density) individuals in excess of this limit are able to feed in nearby patches and thus maintain contact with the other members of their foraging party. When patch density is low, the increased travel costs associated with such a strategy become prohibitive and foraging parties are smaller than or equal to the number of individuals able to feed within a single patch. Females that are routinely excluded from the best feeding sites may have reduced reproductive success because of their low priority of access to resources. These data provide a quantitative link between two ecological variables (resource patch size and density) and fission-fusion social organization in the spider monkey.

The Evolution of Allomothering Behavior Among Colobine Monkeys: Function and Opportunism in Evolution

The great majority of Old World monkey females are interested in infants, particularly very young ones. Characteristically, females will approach infants cradled by their mothers and subsequently attempt to touch or hold them. For Cercopithecine monkeys, the subfamily that includes the baboons and macaques, caretaking attempts by females other than the mother are ordinarily unsuccessful, at least during the first two or three weeks of life. Mothers are highly possessive of their offspring and will not surrender them to substitute infant‐caretakers. In striking contrast, among the other major subfamily of Old World monkeys, the Colobines, mothers readily allow extensive and sometimes prolonged infant carrying and handling by other females (allomothering), even on the first day of life. This paper reviews the traditional functional explanations for these different maternal systems. Stressing opportunism in evolution, the paper suggests that the social and/or genetic benefits alone are not adequate to account for the origins of allomothering behavior among Colobines. Instead, emphasis is given to the kind of ancestral social structure and its environmental context that might allow such a behavioral system to begin. It is hypothesized that, relative to the Cercopithecines, who do not exhibit infant‐sharing, the dental morphology and digestive system of the Colobines produced food‐acquiring and food‐processing advantages that, in effect, reduced intragroup feeding competition and, concomitantly, reduced the importance of status differences between females. Such a social structure could permit the emergence of allomothering behavior since, for all the participants in this activity pattern, there are varying benefits that contribute to individual fitness. [Colobine, allomothering, functions, opportunism, dietary adaptations, social structure]