Polyspecific associations (PSA) occur when 2 or more species maintain proximity or coordinate activities. PSA may provide ecological benefits similar to those of monospecific groups, i.e., protection against predation and improved foraging efficiency, but may also impart costs, such as feeding competition. I studied 3 New World Callitrichidae-Callimico goeldii, Saguinus fuscicollis, and S. labiatus-in northwestern Brazil over 18 mo between April 1999 and August 2003, during which single primary study groups of C. goeldii, S. labiatus, and S. fuscicollis consistently associated with one another. I compared patterns of PSA participation to variation in plant diets during wet and dry seasons. All 3 species associated an average 61% of observation time, but with significant seasonal variation in PSA. During the dry season, AprilSeptember, PSA occurred significantly less frequently than during the wet season, October-March (37% vs. 88%). The variation in PSA corresponded with seasonal shifts in plant food diets, resulting in less dietary overlap among all 3 species during the dry season, particularly between Callimico goeldii and Saguinus labiatus. Dietary richness, diversity, and evenness were also lower in the dry compared to the wet season for each species. The results suggest a link between PSA participation and diet among the taxa; foraging-related costs or feeding competition may constrain PSA during the dry season.
Prehensile tails appear to have evolved at least twice in platyrrhine evolution. In the atelines, the tail is relatively long and possesses a bare area on the distal part of its ventral surface that is covered with der-matoglyphs and richly innervated with Meissner's corpuscles. In contrast, the prehensile tail of Cebus is relatively short, fully haired, and lacks specialized tactile receptors. Little is currently known regarding tail function in capuchins, and whether their prehensile tail serves a greater role in feeding or traveling. In this paper we examine patterns of positional behavior, substrate preference, and tail use in wild white-faced capuchins (Cebus capucinus) inhabiting a wet tropical forest in northeastern Costa Rica. Observational data were collected over the course of 3 months on adult capuchins using an instantaneous focal animal time sampling technique. Differences in the frequency and context of tail use, and the estimated amount of weight support provided by the tail relative to other appendages during feeding/foraging and traveling were used as measures of the ecological role of this specialized organ in capuchin positional behavior. During travel, quadrupedal walking, leaping, and climbing dominated the capuchin positional repertoire. The capuchin tail provided support in only 13.3% of travel and was principally employed during below branch locomotor activities. In contrast, tail-assisted postures accounted for 40.6% of all feeding and foraging records and occurred primarily in two contexts. The tail was used to suspend the individual below a branch while feeding, as well as to provide leverage and weight support in above-branch postures associated with the extraction of prey from difficult to search substrates. A comparison of tail use in Cebus, with published data on the atelines indicates that both taxa possess a grasping tail that is capable of supporting the animal's full body weight. In capuchins and howling monkeys, the tail appears to be used more frequently and serves a greater weight-bearing role during feeding than during traveling. In Ateles, and possibly Brachyteles, and Lagothrix, however, the prehensile tail serves a dual role in both feeding and forelimb suspensory locomotion. Additional relationships between white-faced capuchin feeding, positional behavior, extractive foraging techniques, and prehensile tail use are discussed.
Prehensile tails appear to have evolved at least twice in platyrrhine evolution. In the atelines, the tail is relatively long and possesses a bare area on the distal part of its ventral surface that is covered with der-matoglyphs and richly innervated with Meissner's corpuscles. In contrast, the prehensile tail of Cebus is relatively short, fully haired, and lacks specialized tactile receptors. Little is currently known regarding tail function in capuchins, and whether their prehensile tail serves a greater role in feeding or traveling. In this paper we examine patterns of positional behavior, substrate preference, and tail use in wild white-faced capuchins (Cebus capucinus) inhabiting a wet tropical forest in northeastern Costa Rica. Observational data were collected over the course of 3 months on adult capuchins using an instantaneous focal animal time sampling technique. Differences in the frequency and context of tail use, and the estimated amount of weight support provided by the tail relative to other appendages during feeding/foraging and traveling were used as measures of the ecological role of this specialized organ in capuchin positional behavior. During travel, quadrupedal walking, leaping, and climbing dominated the capuchin positional repertoire. The capuchin tail provided support in only 13.3% of travel and was principally employed during below branch locomotor activities. In contrast, tail-assisted postures accounted for 40.6% of all feeding and foraging records and occurred primarily in two contexts. The tail was used to suspend the individual below a branch while feeding, as well as to provide leverage and weight support in above-branch postures associated with the extraction of prey from difficult to search substrates. A comparison of tail use in Cebus, with published data on the atelines indicates that both taxa possess a grasping tail that is capable of supporting the animal's full body weight. In capuchins and howling monkeys, the tail appears to be used more frequently and serves a greater weight-bearing role during feeding than during traveling. In Ateles, and possibly Brachyteles, and Lagothrix, however, the prehensile tail serves a dual role in both feeding and forelimb suspensory locomotion. Additional relationships between white-faced capuchin feeding, positional behavior, extractive foraging techniques, and prehensile tail use are discussed.
For arboreal primates, ground use may increase dispersal opportunities, tolerance to habitat change, access to ground-based resources, and resilience to human disturbances, and so has conservation implications. We collated published and unpublished data from 86 studies across 65 localities to assess titi monkey (Callicebinae) terrestriality. We examined whether the frequency of terrestrial activity correlated with study duration (a proxy for sampling effort), rainfall level (a proxy for food availability seasonality), and forest height (a proxy for vertical niche dimension). Terrestrial activity was recorded frequently for Callicebus and Plecturocebus spp., but rarely for Cheracebus spp. Terrestrial resting, anti-predator behavior, geophagy, and playing frequencies in Callicebus and Plecturocebus spp., but feeding and moving differed. Callicebus spp. often ate or searched for new leaves terrestrially. Plecturocebus spp. descended primarily to ingest terrestrial invertebrates and soil. Study duration correlated positively and rainfall level negatively with terrestrial activity. Though differences in sampling effort and methods limited comparisons and interpretation, overall, titi monkeys commonly engaged in a variety of terrestrial activities. Terrestrial behavior in Callicebus and Plecturocebus capacities may bolster resistance to habitat fragmentation. However, it is uncertain if the low frequency of terrestriality recorded for Cheracebus spp. is a genus-specific trait associated with a more basal phylogenetic position, or because studies of this genus occurred in pristine habitats. Observations of terrestrial behavior increased with increasing sampling effort and decreasing food availability. Overall, we found a high frequency of terrestrial behavior in titi monkeys, unlike that observed in other pitheciids.
Investigations of size variation in fossil and archaeological skeletal assemblages may be complicated by incomplete skeletons, biased representation of sexes, and the lack of morphological features that identify sex. In order to refine our ability to evaluate size variation, we test the accuracy of three methods that are currently used to estimate size differences in unsexed (pooled) samples: the means method, the median method, and a newly applied technique, the method of moments. Using body mass data from 42 primate species, we calculated actual levels of sexual dimorphism for each species and compared these values to estimates produced by each method. Multivariate regression was used to examine the effects of sample distribution characteristics, including sample size, kurtosis, skewness, sample variance, sex ratio, and intrasexual variance on the performance of the methods. None of the methods appears to be especially accurate. However, one of the simplest methods, the means method, performs relatively well. Factors that lead to inaccuracies in estimation are not readily evident based on multiple regression analysis. We urge caution in the utilization of these techniques, and advocate further analysis of simulated data. Am J Phys Anthropol 110: 95-104, 1999.
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