Thesis (M.S.)--University of North Carolina at Greensboro, 2007. / Title from PDF t.p. (viewed Oct. 18, 2007). Directed by Matina C. Kalcounis-Rüppell; submitted to the Dept. of Biology. Includes bibliographical references (p. 26-30).

If dispersal is reduced on islands, then the demography of island populations of deer mice should be different from that of mainland populations., Areas of 1.1 ha were periodically cleared of mice on Samuel Island (206 ha) and Saturna Island (3102 ha) in the Gulf Islands of southwestern British Columbia., A similar experiment was conducted on the mainland at Maple Ridge, B.C., The average density of mice per hectare on Saturna (43.5) was twice that on Samuel Island (22.0) and nearly two and one-half times higher than that on the mainland (18.7). The reproductive rate, as measured by length of breeding season, number of successful pregnancies, proportion of breeding animals, and number of recruits surviving to breed, was much higher on Samuel Island than on either Saturna or the mainland. Survival was lowest on Samuel Island, with little difference between the mainland and Saturna Island., Mice on Samuel Island grew more than five times faster than mainland animals, and Saturna growth rates were double those on the mainland. Island adult males showed very few aggressive tendencies in laboratory behaviour tests compared with the seasonal changes in aggression reported in the literature for mainland deer mice. Dispersal (or colonization) rate was reduced on the two islands compared with that on the mainland. Eecruitment of young animals occurred throughout the breeding season on the islands but was delayed until the end of breeding on the mainland. There was little difference in the demographic attributes of control populations when compared with those of colonist populations on either the mainland or the two islands. These results indicate that seasonal changes in aggressiveness of the adult population may be sufficient but not necessary to determine breeding density and seasonal changes in survival of juvenile deer mice., A more intensive study is reguired, but regulatory processes in populations of Peromy_scus oa&iculatus may be different on islands and perhaps should not be generalized over different geographic areas. / Science, Faculty of / Zoology, Department of / Graduate

This study examined seasonal variability in demography, genetic composition, and behavior, in populations of deermice (Peromyscus maniculatus), Particular attention was paid to the possible role of aggression and dispersal in determining densities. Three types of populations were examined by means of biweekly live-trapping: undisturbed populations, a population removed continuously, and a population removed annually, at the onset of breeding. The two removal experiments sampled dispersing mice. The genetic data consisted of allelic frequencies at three blood protein loci, detected by starch gel electrophoresis: transferrin, an esterase, and glutamate oxalate transaminase. Behavior of field animals was examined in three laboratory tests. Females which began breeding in early spring suffered heavy mortality, and this resulted in a decline in female density. Females heterozygous at only one locus were selected for over this period. Males became aggressive and spaced themselves out as they began breeding, and light-weight, less aggressive males dispersed. This resulted in a decline in male density. While males were breeding, juveniles, particularly juvenile males, survived poorly, and few entered the populations. Light, non-breeding, subordinate males continued to disperse. As breeding stopped, males which continued to breed moved around, and juveniles survived well. The population increased to its maximum density in late fall. Over the winter, survival was good, dispersal low, and spacing behavior at its minimum. Dispersing males were lighter, showed less aggression in a neutral arena, and were more active than resident males. They differed genetically from residents, although there was no evidence of selection on males in control populations. Dispersing females were lighter, showed less exploratory behavior in an unfamiliar maze, and were more active than resident females. Dispersal was not selective in females. Populations settling in a depopulated area continued to differ genetically from control populations, but within two months resembled control populations demographically and behaviorally. The only difference was that a lower proportion of colonists bred, and this was compensated for by recruitment of juveniles from surrounding areas. The major hypotheses suggested by this study are: 1) Spacing out and dispersal of males in the spring is a response to mortality of early-breeding females, and thus it is this latter mortality which determines breeding densities. 2) Dispersal has two components: dispersal of subordinate mice in response to social pressure, and innate dispersal of more spontaneously active mice. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Sadleir (1965) proposes that the survival of juvenile deermice is determined by the aggressiveness of the adult population. During the summer, when adult aggression is high, juvenile survival is poor, but in the fall, when adult aggression is low, juveniles survive well. The purpose of this study is to examine some of the consequences of Sadleir's hypothesis experimentally. Sadleir bases his hypothesis on the observation that the aggressiveness of males changes seasonally. This premise has been reexamined and confirmed. How adult aggression affects juveniles was studied first in the laboratory. Juveniles grow poorly when competing with adults in their home cage. Males appear to be more active aggressors than females, but only aggressive males are capable of inhibiting juvenile growth. Even though juveniles grew slowly when competing with aggressive adults, they seldom died from encounters with adults. In order to avoid the crowded conditions and confinement implicit in the laboratory experiments, the relationship between adult aggressiveness and juvenile growth and survival was reexamined in field experiments. Two partly isolated plots of habitat were used, and on these plots artificial populations of aggressive or docile male deermice were established. Juveniles were then released onto the plots, and their growth and survival followed. In the field, as in the laboratory, juveniles grew poorly when competing with aggressive adults. Since emigration was not restricted in the field, however, juveniles disappeared in significantly greater numbers when the adult population was aggressive than when the adult population was docile. In addition to these experiments, the success of immigrants onto trapped out plots and plots with a resident population was examined. Immigrants were more successful in establishing themselves on trapped out plots. All the data collected support Sadleir's hypothesis, and it seems reasonable to conclude that the correlation he drew between adult aggressiveness and juvenile survival is real. However, the data collected also provide some interesting clues as to the organization of deermouse populations. An organization is proposed in which the social unit is an animal and its immediate neighbours. Within the social unit mutual antagonism is reduced. But the members of the unit maintain a high level of aggressiveness, and are intolerant of any stranger that wanders into their home ranges. The system proposed would prevent immigrants from settling, while conserving energy by reducing antagonism between familiar animals. The system would also effectively regulate population size. / Science, Faculty of / Zoology, Department of / Graduate

Effects of infections with sylvatic species Trichinella, T. nativa or T. pseudospiralis, on the diel locomotory activity and locomotory activity pattern of an indigenous rodent host, the deer mouse (Peromyscus maniculatus), were assessed in a familiar environment and during the process of familiarization in a novel environment. Infection with muscle-encapsulating T. nativa severely reduced overall locomotory activity and changed locomotory activity patterns in a dose dependent fashion. In contrast, T. pseudospiralis infection had no such effects on diel locomotory activity. Infection with these nonencapsulating nematodes also changed locomotory activity patterns, but effects were independent of inoculation dose. Trichinella pseudospiralis infection almost completely reversed the locomotory exploration patterns of mice. Both T. nativa- and T. pseudospiralis-infected mice spent more time in shelter than did sham-inoculated conspecifics. Biological characterization of these infections in deer mice revealed striking departures from the conventional course of infection as typified by synanthropic trichinellosis in laboratory mice, and provided further insight into the relationship between the major phases of infection and the observed behavioral changes. Altered behaviors of infected deer mice are discussed in terms of their consequences on host fitness and survival, as well as parasite transmission. The study establishes links between behavioral observations derived from synanthropic and laboratory rodent-T. spiralis host-parasite associations and their sylvatic counterparts. It provides the behavioral underpinnings for future assessments of the role of wild rodents in the transmission of sylvatic trichinelloses.

No description available.

This study was initiated after finding two chromosomal types of Peromyscus maniculatus north and south of the Red River in Texas and Oklahoma. The problem was to explain the chromosomal variations and their implications to the systematics of the grassland subspecies of P. maniculatus in this region.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 154-164). Also available via the Internet.

A number of field studies suggest that some vertebrate populations are limited by spacing behaviour, , Small mammals of the genus Peromyscus and Microtus exhibit spacing behaviour by possessing home ranges, but they have contrasting patterns of population fluctuation, Deermice (Peromyscus sp.) fluctuate annually but maintain fairly constant numbers from year to year, whereas voles (Microtus sp.) 'cycle', reaching peak densities every 2 to 5 years. One use of the home range is for food-gathering, Therefore, these experiments were designed to investigate the influence of food availability on the home range and population dynamics of local deermice and voles (P. maniculatus austerus and M. townsendii). The addition of food in late winter resulted in a doubling of the number of deermice. Immigration was 2.5 times that of an unfed control. This could be explained since resident deermice reduced the size of their home ranges. Deermice populations with extra food increased their reproductive output compared with controls: larger numbers of mice bred, and for longer periods, more young were recruited, they grew faster and reached sexual maturity earlier. It is suggested that the onset and cessation of breeding in deermice are proximate responses to food availability, Deermouse dynamics may be closely tied to the temporal and spatial availability of food through the spatial organisation of individuals. It is also suggested that females, because of their energy demands for lactation, and their influence on the survival of young, may be more sensitive to these food conditions and hence exert a strong influence on deermouse population dynamics. Vole populations with, low- and intermediate-levels of food peaked at twice the control density, and a population with a high-level of food reached seven times control density. Voles immigrated to established populations, and colonized vacant areas in proportion to the food available. Like deermice, residents reduced the size of their ranges. Breeding was enhanced in all fed vole populations. Omnivorous deermice had larger ranges than did the herbivorous voles, but both species responded to extra food by reducing their range size, so the smallest deermouse ranges were the size of large vole ranges. The results indicate that home range size in both species is responsive to food availability, and that the concentration of food in the 'typical' habitats of these small mammals is different. If, as suggested, the heterogeneity of deermouse-food in the forest results in an annual cycle in numbers, then the reduced heterogeneity of vole-food in grasslands may influence vole dynamics. / Science, Faculty of / Zoology, Department of / Graduate