Amy Lu | SUNY: Stony Brook University (original) (raw)
Papers by Amy Lu
American Journal of Primatology, 2004
Socioecological theory suggests a link between the strength of competition for food/safety, rates... more Socioecological theory suggests a link between the strength of competition for food/safety, rates of agonism, structure of dominance hierarchies, and dispersal among group-living females. This study presents preliminary data on agonistic behavior and dominance relationships for female Phayre's leaf monkeys (Trachypithecus phayrei), a species in which females routinely disperse. Behavioral observations were conducted on two groups (four adult females, and five adult females plus two juvenile females, respectively) at Phu Khieo Wildlife Sanctuary, northeast Thailand. Rates of agonistic behavior were analyzed from focal continuous recordings, while dominance hierarchies were constructed from all agonistic behaviors (focal and ad libitum sampling). Overall, female–female agonistic behaviors (aggression, submission, and displacements) occurred at a rate of <0.25 interactions per hour. Agonistic interactions involving food occurred more frequently than expected based on feeding time. Females in both groups exhibited linear dominance hierarchies with some reversals, and possibly an age-inversed hierarchical structure in the larger group. The results fit well with previous results for colobine monkeys regarding frequency of interactions, displacements predominating agonistic behavior, and the possibility of an age-inversed hierarchy. The results contradict the suggested link between linearity of hierarchies and female philopatry. Future studies should consider the notion that female dispersal may coexist with linear dominance hierarchies. Am. J. Primatol. 64:351–357, 2004. © 2004 Wiley-Liss, Inc.
Behavioral Ecology, 2008
Feeding competition is suggested as a major factor constraining group size in social foragers. It... more Feeding competition is suggested as a major factor constraining group size in social foragers. It has, however, been challenging to demonstrate consequences of reduced energy gain in terms of fitness, possibly because social foragers may compensate negative effects of scramble competition via adjustments in time budgets. Herbivorous animals are particularly interesting in this context because their fibrous diet and slow digestion process may make it difficult to adjust time budgets. Here we investigate infant development and reproductive rates in Phayre's leaf monkeys (Trachypithecus phayrei) at Phu Khieo Wildlife Sanctuary, Thailand. The diet of the species consists of 39.0% leaves (maximum 81.2% per month). Our analysis is based on data for 3 groups (185 group months) of different sizes (mean 11.4, 18.3, and 25.8 individuals, respectively). Infant development was significantly slower in the large group, in which infants changed to the adult coat later than in the medium-sized group (20.3 vs. 26.3 weeks) and were older when weaned (18.3, 19.7, and 21.4 months, respectively). The interbirth interval after a surviving infant significantly increased with group size (21.3, 22.8, and 24.5 months) while rearing success did not differ (77.8%, 76.5%, and 82.4%, survival to 2 years). Thus, infants in the large group developed more slowly were weaned later and females reproduced more slowly. With similar infant survival rates, these different reproductive rates indicate fitness differences across groups. As in other herbivores, these group-specific differences may reflect scramble competition for food or differences in habitat quality.
Female reproduction is known to be influenced by food availability and its impact on energetic st... more Female reproduction is known to be influenced by food availability and its impact on energetic status. However, emerging evidence suggests that the phytochemical content of food may also be an important factor. Here, we investigated this hypothesis, presenting 20 months of data on fecal progestin (fP) patterns in wild female Phayre's leaf monkeys (Trachypithecus phayrei crepusculus). We examined whether (a) the availability of Vitex (a plant known to contain phytochemicals) might be linked to seasonal fP levels, (b) fP levels were associated with female reproductive performance, and (c) reproductive performance might also be linked with energetic status (as measured by physical condition). We collected fecal samples (N = 2077) from 10 adult females to analyze estrogen (fE) and progestin (fP) metabolites, behavioral data from 7 cycling females to determine receptivity, and monthly data on Vitex availability and female physical condition. Seasonally elevated fP levels were found in all females, with higher levels when Vitex leaves and fruits were abundant. During the period of high progestins, females had longer cycle lengths and follicular phases, while receptive periods did not change. Nevertheless, when ovulations occurred, females were more likely to conceive. On the other hand, conceptions were also more likely when physical condition was improving, suggesting that the effects of phytochemicals and energetic status on reproduction may be difficult to separate. Although our results support the predicted effects of Vitex on endocrine and reproductive function, future studies with detailed feeding data and chemical analyses of plants are needed to confirm this finding.
American Journal of Primatology, 2004
Socioecological theory suggests a link between the strength of competition for food/safety, rates... more Socioecological theory suggests a link between the strength of competition for food/safety, rates of agonism, structure of dominance hierarchies, and dispersal among group-living females. This study presents preliminary data on agonistic behavior and dominance relationships for female Phayre's leaf monkeys (Trachypithecus phayrei), a species in which females routinely disperse. Behavioral observations were conducted on two groups (four adult females, and five adult females plus two juvenile females, respectively) at Phu Khieo Wildlife Sanctuary, northeast Thailand. Rates of agonistic behavior were analyzed from focal continuous recordings, while dominance hierarchies were constructed from all agonistic behaviors (focal and ad libitum sampling). Overall, female–female agonistic behaviors (aggression, submission, and displacements) occurred at a rate of <0.25 interactions per hour. Agonistic interactions involving food occurred more frequently than expected based on feeding time. Females in both groups exhibited linear dominance hierarchies with some reversals, and possibly an age-inversed hierarchical structure in the larger group. The results fit well with previous results for colobine monkeys regarding frequency of interactions, displacements predominating agonistic behavior, and the possibility of an age-inversed hierarchy. The results contradict the suggested link between linearity of hierarchies and female philopatry. Future studies should consider the notion that female dispersal may coexist with linear dominance hierarchies. Am. J. Primatol. 64:351–357, 2004. © 2004 Wiley-Liss, Inc.
Behavioral Ecology, 2008
Feeding competition is suggested as a major factor constraining group size in social foragers. It... more Feeding competition is suggested as a major factor constraining group size in social foragers. It has, however, been challenging to demonstrate consequences of reduced energy gain in terms of fitness, possibly because social foragers may compensate negative effects of scramble competition via adjustments in time budgets. Herbivorous animals are particularly interesting in this context because their fibrous diet and slow digestion process may make it difficult to adjust time budgets. Here we investigate infant development and reproductive rates in Phayre's leaf monkeys (Trachypithecus phayrei) at Phu Khieo Wildlife Sanctuary, Thailand. The diet of the species consists of 39.0% leaves (maximum 81.2% per month). Our analysis is based on data for 3 groups (185 group months) of different sizes (mean 11.4, 18.3, and 25.8 individuals, respectively). Infant development was significantly slower in the large group, in which infants changed to the adult coat later than in the medium-sized group (20.3 vs. 26.3 weeks) and were older when weaned (18.3, 19.7, and 21.4 months, respectively). The interbirth interval after a surviving infant significantly increased with group size (21.3, 22.8, and 24.5 months) while rearing success did not differ (77.8%, 76.5%, and 82.4%, survival to 2 years). Thus, infants in the large group developed more slowly were weaned later and females reproduced more slowly. With similar infant survival rates, these different reproductive rates indicate fitness differences across groups. As in other herbivores, these group-specific differences may reflect scramble competition for food or differences in habitat quality.
Female reproduction is known to be influenced by food availability and its impact on energetic st... more Female reproduction is known to be influenced by food availability and its impact on energetic status. However, emerging evidence suggests that the phytochemical content of food may also be an important factor. Here, we investigated this hypothesis, presenting 20 months of data on fecal progestin (fP) patterns in wild female Phayre's leaf monkeys (Trachypithecus phayrei crepusculus). We examined whether (a) the availability of Vitex (a plant known to contain phytochemicals) might be linked to seasonal fP levels, (b) fP levels were associated with female reproductive performance, and (c) reproductive performance might also be linked with energetic status (as measured by physical condition). We collected fecal samples (N = 2077) from 10 adult females to analyze estrogen (fE) and progestin (fP) metabolites, behavioral data from 7 cycling females to determine receptivity, and monthly data on Vitex availability and female physical condition. Seasonally elevated fP levels were found in all females, with higher levels when Vitex leaves and fruits were abundant. During the period of high progestins, females had longer cycle lengths and follicular phases, while receptive periods did not change. Nevertheless, when ovulations occurred, females were more likely to conceive. On the other hand, conceptions were also more likely when physical condition was improving, suggesting that the effects of phytochemicals and energetic status on reproduction may be difficult to separate. Although our results support the predicted effects of Vitex on endocrine and reproductive function, future studies with detailed feeding data and chemical analyses of plants are needed to confirm this finding.