Presented as Thesis (Ph. D.)--University of Wisconsin--Madison, 1934. / Reprinted from American journal of anatomy, vol. 54, no. 3 (15 May 1934). Includes bibliographical references (p. 506).

An introduced population of Sciurus carolinensis planted at Stanley Park, Vancouver, B.C. about 1913 has maintained itself successfully for at least 38 years in competition with the indigenous squirrel Sciurus douglasi. This population was studied through a period of 18 months. It was found that the gray squirrel has reached a point of saturation in the mixed deciduous-conifer forest type favored by it. The spring population approximates .7 per acre and the autumn population about 1 per acre. Two litters are born per year to adult squirrels, one to yearlings. These arise from matings in March and April and June and July. The ratio between breeding females and young at weaning age is 1 to 1.6, indicating a very low reproductive success. The gray squirrel is not territorial in its behavior. Females move through an area of 5 to 15 acres with little seasonal variation. In the winter the males have about the same range of movements as the females but during the rest of the year they move in a non random manner over an area of 50 to 55 acres. Polygamy is the rule with several males competing for the receptive female. Dominance among such a group of males is positive, physical and not associated with territory. The most important food plants are the vine maple (Acer circinatum) and the broad-leafed maple (Acer macrophyllum). Food storage takes place in a random fashion within a radius of 50 feet from the source. Subsequent recovery of stored food is by random searching over the storage area. The Douglas squirrel exerts physical dominance over the gray squirrel but has a different habitat preference that reduces competition between the two species. Twenty-six birds nests were watched in the squirrel area and only two were destroyed by them. / Science, Faculty of / Zoology, Department of / Graduate

Spermophilus lateralis, the golden-mantled ground squirrel, while euthermic exhibits a strong hypoxic ventilatory response, but a relatively blunted hypercapnic ventilatory response similar to other semi-fossorial mammals. Under resting conditions, carotid body chemoreceptors provide a tonic excitatory input to the frequency component of ventilation. Carotid body denervation (CBX) results in a 40% decrease in minute ventilation (V). The overall ventilatory response to hypoxia is unaffected by CBX, although the ventilatory threshold is significantly shifted to lower levels of inspired O₂. CBX also has little effect on the overall response to hypercapnia. Thus, in S. lateralis, it appears that changes in the partial pressure of O₂ (P0₂) In the blood act centrally, rather than peripherally, to play a predominate role in ventilatory control. Chronic exposure to hypoxia and hypercapnia (CHH, 17% O₂ and 4% CO₂) does not result in overall ventilatory acclimation, with minute ventilation being similar to control squirrels acutely exposed to hypoxic and hypercapnic conditions. In spite of this, CHH exposure does result in adjustments to respiration; frequency is decreased and tidal volume is elevated compared to control squirrels acutely exposed to CHH conditions. Overall V sensitivities to both hypoxia and hypercapnia are not significantly altered by CHH exposure. It appears that acclimation to chronic hypoxic and hypercapnic conditions in S. lateralis may increase alveolar minute ventilation relative to total minute ventilation and thus minimize the changes in arterial PO₂ and Pco₂ during hypoxic and hypercapnic exposure. During entrance into hibernation, as metabolic rate and body temperature decline, concomitant decreases in ventilation occur. Two patterns of respiration occur during deep hibernation; a burst breathing pattern characterized by long non-ventilatory periods (Tnvp) separated by bursts of several breaths and a single breath pattern characterized by single breaths separated by a relatively short Tnvp. In S. lateralis during hibernation at body temperatures between 6° and 10°C, a burst breathing pattern prevails. At slightly lower body temperatures, less than 4°C, a single breath breathing pattern prevails. Both burst breathing and single breath breathing squirrels have similar overall levels of resting minute ventilation. Burst breathing squirrels exhibit a significant respiratory response to hypoxia (3% O₂) and when the decreases in metabolic rate during hibernation are taken into account (air convection requirement) their hypoxic sensitivity is similar to that in awake S. lateralis. In contrast, single breath breathing squirrels do not respond to hypoxia at any level tested (down to 3% O₂). Both burst breathing and single breath breathing squirrels show large ventilatory repsonses to hypercapnia. In the burst breathing state hypercapnic sensitivity is significantly higher compared to the single breath breathing state, due to an augmented frequency response during burst breathing. In both groups of hibernating squirrels ventilation is increased during hypercapnia solely by decreases in the nonventilatory period. When ventilation is standardized for the decreases in metabolic rate during hibernation both burst breathing and single breath breathing S. laterlis exhibit a much higher hypercapnic sensitivity than that seen in awake S. lateralis. Carotid body denervation has little effect on ventilatory pattern generation or ventilatory sensitivities to hypoxia and hypercapnia in hibernating squirrels. It appears that during hibernation in S. lateralis, ventilation is controlled primarily by changes in the partial pressure of CO₂ (Pc0₂) in tne blood acting centrally to stimulate ventilation. The burst breathing pattern is produced centrally, as are the respiratory responses to hypoxia and hypercapnia. Thus, central mechanisms involved with ventilatory control are extremely important in both the euthermic state and the hibernating state, but the chemical stimuli regulating ventilation appear to be fundamentally different in euthermic and hibernating S. lateralis. / Science, Faculty of / Zoology, Department of / Graduate

Sexual selection is considered a powerful evolutionary force responsible for the enormous diversity found in reproductive morphology, physiology, and behavior. I addressed questions related to selection in the Cape ground squirrel (Xerus inauris), a species characterized as highly social and promiscuous. These attributes often are responsible for variance in male reproductive success and as such, sexual selection theory predicts increased opportunity for sexual selection. I confirm that the predominant mechanism underlying genital evolution and competition for paternity in X. inauris is sperm competition. I find evidence that investment in sperm competition is costly and may reflect immunocompetence. I quantify reproductive success as it relates to alternative male tactics and female resource distribution. I find that male X. inauris alternative reproductive tactics differ within and across populations most likely due to differences in female resource distribution. In areas where females are evenly distributed, dispersed males encounter more estrous females, and therefore have increased breeding opportunities. However, the decision to remain natal does not preclude reproduction. I determine that these tactics are most likely conditional with equal fitness payoffs. Males, regardless of tactic, invest more in post-copulatory competition (e.g. sperm competition, copulatory plugs) than males within a population with a clustered distribution of breeding females. In the latter area, males form dominance hierarchies that affect copulatory success and lead to greater skews in reproduction among males. Both sites have evidence of a highly skewed variance in reproduction and intense sexual selective pressure. My results suggest these populations have increased opportunities for selection but that different mechanisms of intrasexual competition may result in rapid evolutionary change within this species.

The genetic structure of 26 natural populations of three species (S. tridecemlineatus, S. mexicanus, and S. spilosoma) of the Ictidomys subgenus of ground squirrels was analyzed using chromosomal and electrophoretic techniques. Chromosomal variation was not observed in S. mexicanus, and only slight karyotypic variation was found in the other two species. Chromosomal evidence indicated hybridization between S. tridecemlineatus and S. mexicanus, placing these species within the classical definition of semispecies. Analysis of electrophoretic variation at 29 genetic loci indicated close genetic relationships between these species. Evolution in Ictidomys appears to be linked with Pleistocene events, and speciation appears to have occurred within the last 155,000 years.

I studied round-tailed ground squirrels (Spermophilus tereticaudus) to determine if presence of water or green vegetation significantly increased reproductive success. I compared the number of juveniles produced, body weights, and diets of squirrels during 1981-84 on 2 plots with green vegetation and no free water, on 3 plots with free water and no green vegetation, and 2 control plots. Reproductive success and body weights of adult and juvenile squirrels were significantly higher (P ≥ 0.001) on plots with green vegetation than on either watered or control plots. Body weights of squirrels on plots with water only and control plots were not significantly different (P ≥ 0.05). Adult squirrels without access to green vegetation during winter and spring failed to reproduce even though free water was readily available. Percent of diet overlap, diversity, and evenness of squirrel diets on control and watered plots were not significantly different. Green vegetation appeared to be the limiting factor for round-tailed ground squirrels.

The tropical forests of South and Southeast Asia hold the highest gliding squirrel diversity but our knowledge of species diversity, ecology and major threats is limited. The present study was undertaken in Arunachal Pradesh, Northeast India between June 2011 and March 2015 to address the paucity of data available on gliding squirrels. Based on field and literature surveys, 14 species of gliding squirrels were detected in the state of Arunachal Pradesh. However, species such as Biswamoyopterus biswasi, which is reported as endemic to Namdapha National Park, were not detected. The high gliding squirrel diversity in this region could be related to a diversity of forest types and its location between the Himalayas and the Indomalayan region. Encounter rates with four different species revealed that Petaurista petaurista was most frequently detected in Namdapha National Park. Major threats include hunting for traditional medicine, cultural purposes or bushmeat, and habitat loss due to forest degradation caused by shifting cultivation. In addition, more intensive studies on population, ecology and conservation status are needed in order to design species and site specific conservation action plans in this region which represents the highest diversity of gliding squirrels globally.

The western gray squirrel (Sciurus griseus griseus Ord) occur only in the Pacific states and in a small corner of extreme western Nevada. Field studies of aspects of the ecology of the most widely distributed subspecies of western gray squirrel (S. griseus) were conducted at three sites in the ponderosa pine-Oregon white oak zone on the eastern slopes of Mt. Hood, Wasco County, Oregon, between 1981 and 1989. From 1981 through 1987, a Hunter Cooperation Program provided remains of squirrels shot during the annual late summer-early autumn hunting season. Other data were gathered through capture and release studies, radiotelemetry, and habitat analysis. The age structure of these populations, as revealed by examination of squirrels killed by hunters, is predominantly mature animals. Also, the population as estimated by hunter success during the Hunter Cooperation Program and by field observations appears to be declining. In the sites studied, western gray squirrels have two seasons of reproductive activity annually. Some individuals mate from January through March; their young emerge from the nest in May and June. Other individuals mate during May and June; their young emerge in August and September. The latter matings are usually the most productive. Analysis of nest trees and their surroundings revealed that nests are most likely to be located in mature trees that have well-developed crowns and occur in stands with a high degree of canopy closure. Nest trees were usually located within approximately 180 meters of permanent water and on sites with a south-southeasterly exposure. Home ranges of squirrels examined in this study were usually large compared to home ranges reported for this species elsewhere in its range. Given the cost of having large home ranges, it seems possible that the squirrels at these study sites exist in less than optimal ecological circumstances. Human factors that may have contributed to the decline of the populations in this study may include the nature of logging activities and the timing of the annual hunting season. Limiting factors other than human activities may include competition with other mast-consuming animals (mule deer, elk, wild turkeys, and three other species of squirrels) for limited and variable mast crops.

Multivariate statistical techniques were applied to the development of habitat suitability models for the Mt. Graham red squirrel, an endangered species. A digital map data base and a geographic information system (GIS) were used to support the analysis and provide input for two logistic multiple regression models. Squirrel presence/absence is the dichotomous dependent variable whose probability the models pretend to predict. Independent variables are a set of environmental factors in the first model, and locational variables in the second case, where a logistic trend surface was developed. Bayesian statistics were then used to integrate the models into a combined model. Potential habitat losses resulting from the development of an astronomical observatory were assessed using the environmental model and are found to represent about 3% of currently available habitat.

Sciurids are one of the most diverse mammalian groups today, but the fossil record does not reflect that diversity. The purpose of this project was to identify sciurids from two late Miocene sites—the Gray Fossil Site (GFS) of Tennessee, and Tyner Farm of Florida—and use those identifications to infer the ecology of the two. From the GFS four sciurids were identified: Eutamias or Neotamias, Glaucomys, and two tree squirrels (Sciurini). Two sciurids were identified from Tyner Farm: a chipmunk attributed to Tamiina, and a ground squirrel attributed to Marmotina. Paleoenvironmental inferences based on the sciurids present at both sites are consistent with previous work. The GFS Eutamias or Neotamias is the first record of a western chipmunk population in eastern North America; the GFS tree squirrels are the earliest record of a tree squirrel in eastern North America. The GFS Glaucomys is the earliest record of the genus.