Thesis (M.S.) in Wildlife Ecology--University of Maine, 2002. / Includes vita. Includes bibliographical references (leaves 62-66).

A study of the biology of the vole, Microtus oregoni serpens, was carried on on the campus of the University of British Columbia, Vancouver, B.C. It was undertaken for a full calendar year and included field study consisting of an examination of the area for preferred habitats, for types of cuttings and for types of runways. This was supplemented by laboratory examination of snap trapped animals for ectoparasites and for the condition of the reproductive systems. Captive animals were studied to obtain additional information on their reproductive biology and habits. In some respects, M.o. serpens was found to be similar to other species of Microtus, such as M.agrestis. In both cases the female has a post parturient heat and a. lactation anestrum, and was also found to control the length of the breeding season. The age of reaching sexual maturity is somewhat similar. The activity pattern is also similar in that both show increased activity at night. M.o. serpens differs from the other species of Microtus in having a longer gestation period and in having smaller litters. In the area studied, this vole was found to be an animal of the forest edge and seral stages. / Science, Faculty of / Zoology, Department of / Graduate

Female and male mammals have different behavioral strategies for maximizing their reproductive success. Pregnancy and lactation obligate female mammals to provide greater parental investment than males; thus, females compete with each other for food and space to rear their offspring, while male mammals compete with each other for female mates. Therefore, natural selection should favor any behavior among females that increases their access to food and space to rear successful offspring and any behavior among males that increases their access to females. In two enclosure experiments, the gray-tailed vole, Microtus canicaudus, was used as a model species to study (1) the relative influence of male competition versus access to females on space use by males and (2) facultative sex-ratio adjustment at the population level in response to low and high population densities, skewed adult sex ratios, and season. Home-range sizes of male voles did not appear to expand beyond an overlap with about five members of either sex. Intrasexual competition with 3-4 males and/or overlap with five females appear to set the upper limits to home-range size. Space use by males is influenced by intrasexual competition and by access to females with an upper limit of overlap with either sex. Additionally, facultative sex-ratio adjustment in response to changing population densities and skewing adult sex ratios did not occur, but a seasonal effect was detected with significantly more males produced in autumn than in spring. Under the conditions of this experimental study, I was not able to measure sex ratios of individual litters, but if any sex-ratio adjustment occurred in response to densities and adult sex ratios, it was not detectable at the population level. / Graduation date: 1999

The 3-5 year cyclical fluctuations in populations of many vole and lemming species have perplexed ecologists for many years. Numerous hypotheses have been proposed to explain microtine rodent cycles, including various aspects of social behavior. Microtine rodents commonly form kin groups composed of related females. Charnov and Finerty (1980) proposed that the formation and breakup of kin groups could, in part, explain the rates of population increase and decline associated with cycles. My experiment sought to determine if kin groups provided population-level benefits in gray-tailed voles, Microtus canicaudus. I compared unmanipulated populations with populations in which kin-structuring was experimentally disrupted to determine if kin groups affected population growth rates and size, reproduction, pregnancy and lactation rates, and recruitment, movement and survival of juveniles. I monitored demography and reproductive behavior in eight 0.2 ha experimental enclosures during a summer breeding season. I found no differences in demographic or female reproductive parameters between control and treatment enclosures, with the exception of a delayed time to first pregnancy for females introduced into the treatment enclosures. In addition, I found no differences in the time to sexual maturation or dispersal movements of juvenile males between control and treatment enclosures. I conclude that disrupting the formation of kin groups does not adversely affect demographic or reproductive parameters at the population-level in gray-tailed voles, and suggest that the contribution of kin groups to social behaviors that may affect population regulation is probably quite small. / Graduation date: 1998

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1962. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 80-85).

In an experimental field study, populations of gray-tailed voles (Microtus canicaudus) were exposed to a commercial formulation of vinclozolin, a fungicide effective for disease control on ornamental plants, turf grasses, and fruits and vegetables. Vinclozolin has been shown in laboratory experiments to behave as an androgen antagonist, impairing the reproductive development in males of several species of mammals when exposed in utero. However, when applied to grassland habitat containing populations of gray-tailed voles, no biologically significant impairment was observed in reproductive development of male voles whose mothers were exposed to the treatment while the young were in utero. Reproductive organs were sufficiently developed to result in high reproductive rates and juvenile recruitment in the field with no effects on population growth or demography. Under the conditions of this study, one standard application of Curalan[copyright] fungicide had no measurable reproductive or demographic consequences on gray-tailed voles. However, the results suggest that higher application rates or several successive applications may have negative impacts on reproductive development and demography of wild vole populations. / Graduation date: 1999

A number of field studies on small mammals have suggested that aggressive behavior may limit breeding density. To investigate how the presence of one individual affects another's chances for survival, reproduction, and growth, I carried out a series of experimental studies on Microtus townsendii near Vancouver, Canada. In the first experiments, population density was reduced by removing voles before or during the spring decline. Drastic artifical reduction during a spring decline improved female survival but not male survival; similar reduction in the fall prior to a decline improved both male and female survival. Survival was not density-dependent in males, but was in females during one decline. To explain these results, a behavioral model is proposed in which females compete for nest sites and males compete for females. In a second experiment, a population predicted to experience a decline was enclosed. I wanted to see if preventing emigration would stop the decline. Unfortunately the control area remained at peak densities and neither area suffered a spring decline. The enclosed population had higher rates of increase, reached higher densities, and had higher survival rates than those on the control area. This resulted in severe overgrazing and a sharp population decline within the enclosure. These results indicate that movements play a necessary role in population regulation when voles are at peak, densities. In a third experiment, the role of predation in causing population changes was measured. Predation was not necessary to initiate a decline or to maintain it. Of the tagged voles known to have been eaten, there was no consistent selection by predators for either of the saxes, for any weight class, or for voles with any other characteristic that could be measured by live-trapping. Of the total number of voles known to have been eaten, avian predators consistently chose animals that were smaller than those in the tagged population. This indicates that either the live-traps selectively caught large animals, or avian predators selectively caught small animals, or that both biases were present. In the fourth experiment, the role of resident adults in determining juvenile survival was tested by removal of adults and by adding juveniles to experimental populations. Survival of young was improved in the absence of all adults, but not in either intact populations, in reduced populations, or in female populations. Survival of young was better in periods of reduced adult breeding. Height at sexual maturity tended to be higher in the presence of adults of the same sex. Growth in young males tended to be reduced in the presence of adult males. These results indicate that females reduce survival of young, and suggest that emphasis be placed on the study of female behavior as a factor affecting microtine numbers. In the final experiment, the survival and dispersal rates of very young voles were examined to determine where the enormous loss between birth and recruitment occurred. A high density vole population was trapped concurrently with live-traps and pitfall traps. Capture of a large number of young in pitfalls indicated that mortality was higher among post-weanlings than among any other age group. The pitfall traps enumerated up to twice as many animals as the live-traps, and over half of the 1100 animals caught first in pitfalls were never caught in live-traps. Trapping solely with live-traps may severely underestimate numbers (at least when densities are high) and give inaccurate population statistics. Populations of J. townsendii fluctuate in size and Chitty's behavior hypothesis predicts that spacing behavior underlies these density changes. My experimental results are consistent with this general view and add specific details to the mechanism by which density is regulated. My experiments pinpoint post weaning survival as a critical phase determining population changes in this vole and focus attention on two critical areas: adult female - postweanling interactions and adult female-adult female interactions. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 2000. / Title from PDF t.p. (viewed on Dec. 11, 2005). Vita. Includes bibliographical references (p. 36-40).

Previous studies of the control of reproduction in Rhabdomys pumilio have shown that day length alone does not inhibit spermatogenesis, that a reduction in food availability and ambient temperature results in an inhibition of gametogenesis, that females are more susceptible to inhibition than are males, and that mice that are able to maintain a body fat store in the face of an energetic challenge, are less likely to show reproductive inhibition than those that lose their fat store. In the present study, field and laboratory experiments were conducted to examine the effects of winter food supplementation on reproduction and population dynamics, and the effects of exogenous GnRH, leptin and mercaptoacetate (MA) on reproductive activity of Rhabdomys pumilio exposed to an energetic challenge. In the field food supplementation experiments in Thomas Baines Nature Reserve (2000, 2001), there was no winter inhibition of reproduction and provision of supplementary food had little effect. While at Mountain Zebra National Park (2002) winter was harsher, females became reproductively inactive, spermatogenesis continued and the provision of extra food resulted in higher rates of individual growth and larger reproductive organs. Treatment of mice that had been exposed to a prolonged energetic challenge, with exogenous GnRH (1µg/mouse/treatment) resulted in an increase in the masses of the testes and epididymides, and in the activity of the reproductive organs. Treatment with exogenous leptin (40µg/mouse/treatment), concurrently with an energetic challenge, countered the negative effects of the energetic challenge, and treated males had larger reproductive organs. MA (600µmol/kg body mass), given concurrently with an energetic challenge, did not inhibit fat metabolism, although the high-fat diet countered the effects of the energetic challenge. Results suggest that the first response of male Rhabdomys pumilio to an energetic challenge is a reduction in the size of the reproductive organs, without an inhibition of spermatogenesis. It is likely that this effect is mediated via white fat and leptin, and leptin’s influence on the hypothalamic-pituitary-gonad axis. Results of the study support the suggestion that females are more sensitive to reproductive inhibition than males and that reproduction in Rhabdomys pumilio is truly opportunistic.