This study dealt with the life history and population dynamics of the pine vole, Microtus pinetorum. In the past there has been a void of ecological material concerning this small mammal in the southwestern region of its range. From November, 1969, through February, 1970, a survey was conducted in Marion County and Harrison County, Texas, to determine the most suitable habitat for an ecological study of Microtus pinetorum. A study was then initiated in March, 1970, and continued through March, 1971, on an undisturbed marsh five miles south of Marshall, Harrison County, Texas.

Clark’s Cave contains a large collection of late Pleistocene mammal material. In particular, it contains a sizable amount of Microtus spp. which can be valuable paleoclimate indicators. Identification techniques traditionally used to classify these species have been shown to be unreliable. Recent studies have shown that using geometric morphometric techniques on lower first molars can be more successful. By placing landmarks and running a discriminate analysis on new and previously collected material from the cave, significant differences in Microtus species proportions were found. Specifically, showing the deposit has a larger proportion of M. xanthognathus than previously reported; resulting in a subsequent drop in the number of M. pennsylvanicus and M. chrotorrhinus present. Moreover, previously unreported M. ochrogaster was determined to be an important component of the fauna. The results presented here show the importance of applying new techniques to previous studies.

Thesis (M.S.)--Florida State University, 2003. / Advisor: Dr. Zuoxin Wang, Florida State University, College of Arts and Sciences, Dept. of Psychology. Title and description from dissertation home page (viewed Oct. 1, 2003). Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1955. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 117-120).

This thesis focuses on individually specific differences in behavioural strategies, personalities, with two microtine rodents (Microtus arvalis and M. oeconomus) as study species. The work evaluates methodology necessary to reveal and measure consistent individual differences in behaviour, identifies possible proximate and ultimate mechanisms behind the existence of individual behavioural variability, and describes some ecological, evolutionary and behavioural consequences of personalities.

Cranial and external measurements in 422 museum specimens of the common vole, Microtus arvalis, from Switzerland were examined to determine whether they varied with altitude in accordance with either (1) Bergmann's Rule, or (2) subspeciation. Correlation coefficients between altitude and size were calculated on 32 dimensions, each of which had been divided into sex segregated age groups. In not one of the 108 tests was correlation significant. The lack of adherence to Bergmann's Rule was investigated by (1) reviewing the basic concepts of the Rule, as applied to homeotherms; (2) identifying the major abiotic and biotic selection pressures that might affect growth in Microtus arvalis, including climate and competition with sympatric congenerics; and (3) indicating deficiencies in data derived from museum specimens which might have influenced the computations. There were several references in the literature to the occurrence of two subspecies of Microtus arvalis in Switzerland - the nominate subspecies M. a. arvalis (Pallas, 1779) and a montane subspecies called either M. a. incertus (Selys-Longchamps, 1841) or M. a. rufescentefuscus (Schinz, 1845). The lack of evidence in this study for the existence of two phenotypically and distributionally distinct subspecies was considered by (1) examining the general appropriateness of discussing variation in Microtus arvalis in terms of subspeciation; and (2) reviewing the literature on the diagnostic characters and distribution attributed to the montane morph. Two major conclusions were drawn. The first was that Bergmann's Rule should not be considered a "rule" until firm definitions are established on at least two of its founding precepts - the groups of animals to which it applies and the taxonomic level at which it applies - and until it is found to apply to a majority of the cases for which it is intended. The second conclusion was that for species like Microtus arvalis, in which growth is highly variable and distribution is by and large continuous, the usefulness of formal recognition of in-fraspecific populations is questionable until an overview of the geographic variability of the species as a whole is well documented. / Science, Faculty of / Zoology, Department of / Graduate

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

Prairie (Microtus ochrogaster) and woodland (Microtus pinetorum) voles, which exhibit distinctly different ecological preferences (grassland versus forest), commonly co-occur in paleontological deposits in eastern North America. Despite their ecological differences, their molar morphology is similar. Assuming that those ecologic differences occurred in the past, differentiation of these two taxa is important for paleoenvironmental reconstruction. A sample of 51 lower first molars from living populations were viewed via scanning electron microscope to qualify and quantify schmelzmuster (enamel microstructure) to species-specific standards applicable to the fossil record. The most obvious differences between schmelzmuster of the two taxa are the relatively thicker bands of radial enamel on the leading edges of triangles of M. ochrogaster, as well as the consistent retention of tangential or primitive tangential enamel on the trailing edges and posterior enamel band of the posterior loop of M. pinetorum. Discriminant analysis of landmark data from the same 51 specimens established morphological boundaries for these taxa and successfully separated the recent m1s of M. ochrogaster from those of M. pinetorum. To test identification confidence from previous work, and to add an independent means of identification for future work (at any site), both techniques were applied to a sample of three-closed triangle (“M. ochrogaster” type) m1s from the late Pleistocene Wapsipinicon Local Fauna of Jones County, Iowa. Identifications of the specimens from the Wapsipinicon l.f. based on schmelzmuster and morphometric analysis are consistent with those reached using traditional morphology. Such methods serve as independent “check” of traditional (qualitative) identification, highlight new species-level characters, and quantify previously described features, for discrimination of these taxa.

M.S.

The microtine rodents Microtus pennsylvanicus and Synaptomys cooperi are sympatric and occur in the same general habitats. Interspecific competition that varies in intensity would be predicted because of similarities in life history characteristics and temporal variation in Microtus density. Microdistribution of Microtus and Synaptomys was monitored during peak, trough, and early increase phases of a Microtus population cycle. Food habits, activity patterns, and behavioral characteristics were also compared. Field studies at seven sites extended from June 1978 to February 1981. These sites represented a range in habitat suitability for Microtus, as indicated by relative population densities. Undisturbed populations of Microtus and Synaptomys were studied to determine the effects of natural changes in Microtus density on Synaptomys microdistribution. Removal of one species or the other from study grids was used as an experimental tool. Vegetation analysis of study sites included estimates of percentage ground cover and tree/shrub density. Discriminant function analysis was used to determine which of 22 vegetation variables contributed most to distinguishing habitats and microhabitats of the two species. The dominant plant species in habitats where Microtus and Synaptomys coexisted were Juniperus virginiana and Andropogon scoparius. Even at peak population levels, Microtus occurred in relatively low densities (17-50/ha). At the low point in a natural population cycle, the decline or disappearance of Microtus was accompanied by a microdistributional shift by Synaptomys into areas formerly occupied by Microtus. This shift occurred when differences in daily activity rhythms were maximal. Recolonization by Microtus during the early increase phase of population growth resulted in a return to the initial distributional pattern. Displacement of Synaptomys occurred when both species were primarily nocturnal. Removal of Microtus from an experimental grid was followed by colonization by Synaptomys. When Synaptomys was removed from an experimental grid, the distribution of Microtus did not change. Behavioral interaction studies revealed high levels of avoidance and aggression, suggesting that spatial separation is behaviorally maintained. Vegetation studies indicated that habitats with heavy ground cover supported permanent Microtus populations and were inaccessible to Synaptomys. Microhabitat partitioning occurred in heterogeneous habitats with sparse ground cover and denser tree canopy. In the presence of Microtus, Synaptomys occupied microhabitats with higher densities of deciduous trees and shrubs, but shifted to more open microhabitats when Microtus was absent. Food habits analysis indicated that Synaptomys diet consists of vegetation that is low in nutrient content (Andropogon in summer, moss in winter). While Microtus will eat Andropogon (especially in winter), this species also included dicots and other monocots in its diet. Synaptomys diet was more diverse when living on a grid from which Microtus had been removed. These findings suggest that in the southern Appalachians, Synaptomys is excluded from preferred habitats by Microtus and, as a result, lives where cover is sparse and food is low in nutritional value. Competition is relaxed when Microtus declines to trough population density. The combination of wider habitat tolerances by Synaptomys and temporal variation in intensity of competition allows coexistence on a regional basis. / Ph. D.