Stephen H. Vessey

Group changing in free-ranging male rhesus monkeys

Group changing behavior of maleMacaca mulatta was studied over a six-year period at the rhesus monkey colony on two coastal islands at La Parguera, Puerto Rico. Males first left their natal group at a mean age of 47 months and became solitary for the first time at a mean age of 64 months; all had left their natal groups by seven years of age. Age, mating season, sex ratios of adult males and females in the social bands, and geographical barriers all had significant effects on the group shifting. Population size, rank of mother or being an orphan did not significantly affect the changing process. Two factors, age (size) and seniority in the group, were important in determining a males rank in his new group.

Dominance rank, secondary sex ratio, and reproduction of offspring in polygynous primates

One question in evolutionary biology which is central to understanding reproductive strategies and parental efforts at rearing offspring is why organisms produce certain offspring sex ratios (Trivers and Willard 1973; Charnov 1982). Fisher (1930) argued that since each individual has a mother and a father, both sexes contribute genes equally to the next generation. All else being equal, if members of one sex were overproduced, their ability to reproduce would be limited by the availability of members of the less abundant sex and natural selection would favor any predisposition to produce offspring of the less abundant sex. In this fashion, Fisher reasoned, selection would adjust the offspring sex ratio in an outbreeding population until total parental investment (PI, Trivers 1972) in the two sexes was equal. Fisher (1930) assumed, but did not clearly state, that all parents were alike in their ability to rear reproductively successful sons and daughters (Patterson and Emlen 1980). A model proposed by Trivers and Willard (1973), however, specified how deviations from equal PI may be favored by natural selection according to the influence of maternal condition on the reproduction of offspring. The TriversWillard model proposed that in polygynous species if some condition of mothers (e.g., dominance rank) influences the condition and, as a result, the reproductive success (RS) of sons more than daughters, then selection should result in the evolution and maintenance of mechanisms by which females in poor condition invest less in sons than daughters and/or females in good condition invest more in sons than daughters. This model is particularly relevant for primates, since the majority of species are polygynous (Clutton-Brock and Harvey 1977). Since the dominance rank of a monkeys social group and family has a strong

Effects of Grouping on Levels of Circulating Antibodies in Mice

Summary The effects of grouping and social rank on circulating-antibody titer were studied using C3H mice. Previously isolated mice were placed together in groups of 6 each for 4 hours per day and injected with beef serum on the fifth day of grouping. Antibody titers were determined from blood samples by the ring precipitin test. Grouped mice were found to have significantly lower titers of circulating antibody than did isolated mice. Dominant mice had significantly higher titers than the other mice in their groups. The adrenal glands of grouped mice, taken after 28 and 38 days of grouping, were significantly heavier than those of isolated mice.

THE EFFECT OF DENSITY DEPENDENCE AND WEATHER ON POPULATION SIZE OF A POLYVOLTINE SPECIES

The identification of what factors determine the population dynamics of polyvoltine species has been a difficult problem in ecology because population dynamics can contain intra- and interannual variability, and because the time scale at which factors affect the population is often unknown. We created a comprehensive population model to determine how density dependence (linear, nonlinear, and time-delayed) and weather affected the rate of population growth of white-footed mice (Peromyscus leucopus) in an isolated woodlot. We studied this nonoutbreak, polyvoltine species using a 257-mo data set spanning 23 yr, which incorporated both detailed intra-annual and long-term dynamics, and we used this model to forecast future population size. We then evaluated whether 3-yr spans of monthly data or a 22-yr span of annual data were better able to identify the key determinants that drive population dynamics, and we identified which data type created more accurate forecasts. The 257-mo comprehensive model determined...

Effects of Small Forest Openings on the Breeding Bird Community in a Vermont Hardwood Forest

We examined the response of a forest bird community to the presence of small openings created by patch clear-cutting 0.4-ha plots within an extensive northern hardwood forest. We conducted bird censuses (June) and habitat measurements (July-August) in 102 census plots at four distances from openings in 1991 and 1992. Of 19 habitat variables measured, none differed significantly among forest plots at any distance from clear-cuts. Thirty-five (70%) of 50 bird species encountered during censusing were Neotropical migrants. Bird species richness did not differ as a function of distance from openings. However, species composition in plots within openings was least similar to that in plots farthest into forest, and most similar between the two distance categories farthest from openings. The movement of several forest-interior species away from openings, the addition of early-successional colonists in openings, and a high abundance of interior-edge species near openings contributed to the difference in species composition between openings and forest plots. As a group, Neotropical forest-interior migrants were significantly less abundant in openings than at any distance from them, and less abundant 50 m from openings than 200 m from them. Neotropical interior-edge migrants were significantly more abundant 50 m from openings than at any other distance. Nearctic migrants and nonmigrants did not respond to the presence of small openings. Of three locally common avian nest predators, none became more abundant in the openings. Brown-headed Cowbirds (Molothrus ater), also common locally, were never observed in or near the openings. Overall, bird species diversity increased in forested areas containing small openings due to the addition of edge and open-area nesters, but several forest-interior species were adversely affected by the presence of openings.

Survival and Dispersal of Young White-Footed Mice Born in Nest Boxes

Thirty-nine litters of white-footed mice ( Peromyscus leucopus ) were followed from birth in nest boxes until establishment of home ranges in an isolated, 2-ha woodlot. The sex ratio at birth was significantly biased toward males in the spring and females in the fall. Mothers were significantly heavier in spring than in fall. In the spring, 39 of 97 pups (40%) were weaned, while in the fall only 8 of 67 (12%) were weaned. After three weeks of age the expectation of further life was more than 9 weeks for spring-born and less than 3 weeks for fall-born mice. Young left the nest at an average age of 5.6 weeks. Mothers consistently retained their home ranges after young dispersed. With the exception of one litter, littermates did not aggregate after dispersal, but scattered throughout the woodlot. Males settled at an average of 75 m from the natal nest, females an average of 39 m. These small dispersal distances, coupled with a near absence of immigration and low spring populations, suggest the possibility of inbreeding.

Longevity and Survival in a Population of White-Footed Mice (Peromyscus leucopus)

We tested the hypothesis that long-lived white-footed mice, Peromyscus leucopus , were phenotypically and behaviorally different from short-lived mice in a 7-year study of a population in northwestern Ohio. Of > 1,800 individuals captured, 2.3% remained in the population >345 days (20 males and 22 females). Post-weaning mortality was nearly constant, but autumn-born mice suffered higher early mortality than did spring-born mice. Females, but not males, had a better chance of reaching old age if they were born in autumn. Comparison of home-range size and body mass did not indicate phenotypic differences between long- and short-lived mice, and long- and short-lived females produced litters at the same rate.

Maternal dominance rank and lifetime survivorship of male and female rhesus monkeys

SummaryThe longitudinal survivorship of a group of free-ranging male and female rhesus monkeys from La Parguera, Puerto Rico, was analyzed. Males had lower age-specific survivorship than females. There were no differences in the survivorship of daughters of high- and low-ranking mothers and there was no correlation between total number of offspring born and maternal rank for females. However, the sons of low-ranking mothers had lower survivorship than the sons of high-ranking females. This sex-related difference in survivorship, in conjunction with other evidence, indicates that the average lifetime reproduction of sons of low-ranking females is lower than that of daughters and vice versa for offspring of high-ranking females.

Paternal Behavior in a Natural Population of White-footed Mice (Peromyscus leucopus)

-Studies demonstrating paternal care in Peromyscus leucopus are conflicting; laboratory evidence suggests that males care for young at an early age, whereas evidence from small enclosures suggests that paternal care does not exist. This study demonstrates the association of fathers with their weaned young in a wild population of P. leucopus. Live trapping, nest boxes, radio telemetry and DNA fingerprinting were used to determine if and when males associate with their own young. We frequently observed adult males alone with juveniles of either sex after they were weaned. Paternity was likely in most cases, and was confirmed by DNA fingerprinting in some cases. We observed an adult male forage with >two young on two occasions. We did not observe adult females in association with weaned juveniles but often observed them with juveniles before weaning. These findings contradict laboratory studies in small cages and studies in small enclosures which did not observe associations of adult males with young after weaning.

Effects of Chlorpromazine on Aggression in Laboratory Populations of Wild House Mice

Three confined, freely growing populations of wild house mice (Mus musculus) were studies to determine possible functions of aggressive behavior in regulating population size. Effects of a tranquilizer, chlorpromazine, on aggression and population parameters were measured. In singly caged pairs of mice chlorpromazine, mixed with the food at a rate of 0.75 mg/g food, significantly increased the number of days between litters. Also, significantly fewer young were born and weaned when compared with pairs given a control diet. Thus chlorpromazine produced no direct enhancement of reproduction. At the same dose chlorpromazine reduced fighting among C57 male mice. The growth curves of the populations prior to treatment were generally sigmoid, upper limits varying in each population. Birth and survival rates of infants declined with increasing population size. Mortality rates of adults did not vary significantly with population size. Due to a higher mortality of post—weaned males than females, sex ratios general...