In any host population, individuals may be infected with multiple pathogens concurrently or in sequence. The direction and strength of pathogen-pathogen interactions are often unknown and dependent on the mechanism of interaction. This thesis is concerned with the epidemiology of infections and coinfections in zebu cattle during their first year of life, and the consequences they have for hosts’ survival probabilities and growth rates. Specifically, the study aims to: a) identify the many different pathogen infections occurring in zebu cattle under one year old, b) identify the main causes of mortality and reduced growth rates, c) test for evidence of effects of pathogen-pathogen interactions on mortality and growth, and d) determine the risk factors for infections with pathogens associated with increased mortality and reduced growth rates in zebu calves. To achieve these aims data collected from an epidemiological follow-up study of a cohort of 548 indigenous zebu cattle, recruited at birth and followed for the entire first year of life was used. Growth rates were enormously variable (52 to 704% of birth-weight) and 88 (16%) of the calves died during the first year, most from infectious disease. In total, 25,104 calf weeks of observation and data from 5,337 individual calf visits were analysed. Over 50 different pathogens were identified in the cohort. The thesis begins by providing an overview of zebu cattle and the importance of cattle diseases relevant to Sub-Saharan Africa, emphasising the importance of epidemiological studies taking into account co-infections, which are common in the natural populations, as opposed to a single-pathogen focus. A detailed description of the study design, data collection and descriptive analysis of non-infectious factors, including management and environmental factors, and a descriptive analysis of all pathogens screened for in the study are provided. Using Cox proportional models with frailty terms, the study then identifies infectious and non-infectious risk factors associated with mortality. Further, the role co-infections play in decreasing survival probabilities are investigated, revealing that the hazard for death from East Coast Fever (ECF) - the single most important disease associated with 40% of all deaths - increases 10 times in animals co-infected with Trypanosoma species, and 1.3 times for every 1000 eggs per gram faeces increase in strongyle egg count. Mixed-effect models are used to study growth rates and the impact of coinfections, revealing both synergistic interactions (lower host growth rates) of T. parva and A. marginale co-infections, and antagonistic interactions (relatively higher host growth rates) of T. parva and T. mutans co-infections compared to single infections with T. parva. Further, this work shows that helminth infections can have a strong negative effect on the growth rates but this is burden-dependent. These findings provide baseline epidemiological data on the diseases with greatest impact on health and performance of young zebu cattle, information that is valuable in the prioritisation and control of diseases. Additionally, they provide evidence of co-infections affecting host growth and survival, and have important implications on disease control strategies, suggesting benefits of aan integrated approach to control of worm, tick and tsetse-borne diseases.

When someone walks into an insurance company and wants to purchase life insurance, the insurance company has to consider an important question: How long will this client live? His date of death is not exactly predictable, so the insurer does not know exactly when the life insurance benefits will be payable. However, the insurer can use a model that can calculate human mortality. With this mortality model, probabilities of deaths at particular ages can be calculated. Rather than trying to figure out when a client dies, the convention in actuarial science is to phrase things in terms of survival models. There are popular survival functions that enable insurers to perform this calculation. With these functions, insurers are able to efficiently provide this service and ensure that life insurance will continue to be a thriving field of work. After we define basic notation and terms, we look at standard survival models. Then we consider a recently proposed model by Chi Heem Wong and Albert K. Tsui.

I studied the habitat selection, survival, and anti-predator behaviors of the fox squirrel (Siurus niger) across the urban-rural gradient in College Station, Texas. From two years of tracking the radio locations of 82 fox squirrels, my data suggested that fox squirrels in urban areas selected for use large mast bearing trees that mimicked the habitat features they prefer in non-urban areas and avoided conifer and ornamental tree species. Urban fox squirrels selected to use buildings and non-native grass during certain seasons and showed a tolerance for pavement, including it proportionally in their core-areas. Analysis of radio-telemetry data of urban and rural fox squirrels suggested that the rates of survival and causes of mortality differed between the two populations. At least 60% of the mortalities on the rural site were caused by predation, while < 5% of the mortalities on the urban site were caused by predation. Most of the mortalities on the urban site (>60%) were cause by vehicular collisions. Observations of anti-predator behaviors supported my hypothesis that squirrels decrease their anti-predator behaviors as the human presence increases. Observational data also supported my hypothesis that this phenomenon was caused by habituation. I also found that the time dedicated to anti-predator behaviors differed among urban, rural, and suburban fox squirrel populations in response to coyote and hawk vocalizations. The mean responses to both vocalizations on the rural site (coyote = 45%, hawk = 55%) were at least twice that of those found on the urban sites (coyote = 11%, hawk = 20%). I also used survey responses to questions about squirrel management to test theoretical frameworks linking attitudes to behaviors. My data suggests that beliefs and attitudes that are modified by variables shown to increase accessibility generally correspond better to behaviors. My data also suggests that the inclusion of a measure of previous behaviors will increase the predictive ability of models within different theoretical frameworks. Most importantly for the advancement of a comprehensive theoretical framework, my study showed that composite models combining components of the theory of reasoned action and attitude to behavioral process models out-performed other models.

No description available.

The raccoon (Procyon lotor) is a species that has likely benefited from environmental conditions that followed European settlement of North America. As such, the raccoon has experienced vast range expansion during the past century, moving northward across the continent. However, little is known about the factors that currently govern the northern distribution and the ecology of raccoons at the northern edge of its range. Thus, I studied the population dynamics and social ecology of raccoons in southern Manitoba during spring, summer, and autumn, 2002-2005.<p>To understand how intrinsic and extrinsic factors affected population dynamics, I examined how winter severity, body condition, age, and gender influenced over-winter survival of raccoons. Winter severity (measured by temperature and snow accumulation) was the most important factor influencing survival (â = 1.08, 95% CI = 0.99-1.17). Over-winter survival estimates ranged from 0.51 (95% CI: 0.41, 0.75) during the harshest winter to 0.84 (95% CI: 0.71, 0.97) during the mildest winter on record for Manitoba. There was no apparent relationship between autumn body condition and autumn food indices and no correlation between autumn and spring body condition. Adults experienced higher survival than yearlings while males had a greater chance of dying compared to females. Variation in abundance natural food items thought to be important during autumn hyperphagia are likely overwhelmed by the presence of grain as an alternative food source, as autumn body condition was constant across all years and plateaued at ca. 20% body fat. I conclude that changes in climatic conditions will likely have the greatest impact on raccoon demographics, with milder winters leading to higher survival. <p>I also examined the spatial ecology of raccoons to determine if spacing behaviour could limit population growth and to test hypotheses regarding social tolerance and the formation of male coalition groups. Female home ranges were regularly spaced throughout the study site, with minimal spatio-temporal overlap among adult females. However, there where instances where females did display tolerance among conspecifics as well as the ability to partition areas of overlap to use them dissimilarly. While females were generally non-gregarious, plasticity in social tolerance likely precludes spacing behavior from regulating densities of this population. Male social behavior was more complex than previously described for northern populations; most adults (ca. 80%) formed a coalition pair with another male. There was little overlap among male groups and high overlap within groups. The dynamic interaction tests confirmed association in movements for male dyads. Male coalition groups formed despite females being regularly spaced, which contradicts working hypotheses of mechanisms explaining grouping behavior in male carnivores. I propose that group formation occurred because of the benefits that dominant males received through increased efficiency in territory maintenance and the increased likelihood of territory inheritance by subordinate males.

The raccoon (Procyon lotor) is a species that has likely benefited from environmental conditions that followed European settlement of North America. As such, the raccoon has experienced vast range expansion during the past century, moving northward across the continent. However, little is known about the factors that currently govern the northern distribution and the ecology of raccoons at the northern edge of its range. Thus, I studied the population dynamics and social ecology of raccoons in southern Manitoba during spring, summer, and autumn, 2002-2005.<p>To understand how intrinsic and extrinsic factors affected population dynamics, I examined how winter severity, body condition, age, and gender influenced over-winter survival of raccoons. Winter severity (measured by temperature and snow accumulation) was the most important factor influencing survival (â = 1.08, 95% CI = 0.99-1.17). Over-winter survival estimates ranged from 0.51 (95% CI: 0.41, 0.75) during the harshest winter to 0.84 (95% CI: 0.71, 0.97) during the mildest winter on record for Manitoba. There was no apparent relationship between autumn body condition and autumn food indices and no correlation between autumn and spring body condition. Adults experienced higher survival than yearlings while males had a greater chance of dying compared to females. Variation in abundance natural food items thought to be important during autumn hyperphagia are likely overwhelmed by the presence of grain as an alternative food source, as autumn body condition was constant across all years and plateaued at ca. 20% body fat. I conclude that changes in climatic conditions will likely have the greatest impact on raccoon demographics, with milder winters leading to higher survival. <p>I also examined the spatial ecology of raccoons to determine if spacing behaviour could limit population growth and to test hypotheses regarding social tolerance and the formation of male coalition groups. Female home ranges were regularly spaced throughout the study site, with minimal spatio-temporal overlap among adult females. However, there where instances where females did display tolerance among conspecifics as well as the ability to partition areas of overlap to use them dissimilarly. While females were generally non-gregarious, plasticity in social tolerance likely precludes spacing behavior from regulating densities of this population. Male social behavior was more complex than previously described for northern populations; most adults (ca. 80%) formed a coalition pair with another male. There was little overlap among male groups and high overlap within groups. The dynamic interaction tests confirmed association in movements for male dyads. Male coalition groups formed despite females being regularly spaced, which contradicts working hypotheses of mechanisms explaining grouping behavior in male carnivores. I propose that group formation occurred because of the benefits that dominant males received through increased efficiency in territory maintenance and the increased likelihood of territory inheritance by subordinate males.

I studied the habitat selection, survival, and anti-predator behaviors of the fox squirrel (Siurus niger) across the urban-rural gradient in College Station, Texas. From two years of tracking the radio locations of 82 fox squirrels, my data suggested that fox squirrels in urban areas selected for use large mast bearing trees that mimicked the habitat features they prefer in non-urban areas and avoided conifer and ornamental tree species. Urban fox squirrels selected to use buildings and non-native grass during certain seasons and showed a tolerance for pavement, including it proportionally in their core-areas. Analysis of radio-telemetry data of urban and rural fox squirrels suggested that the rates of survival and causes of mortality differed between the two populations. At least 60% of the mortalities on the rural site were caused by predation, while < 5% of the mortalities on the urban site were caused by predation. Most of the mortalities on the urban site (>60%) were cause by vehicular collisions. Observations of anti-predator behaviors supported my hypothesis that squirrels decrease their anti-predator behaviors as the human presence increases. Observational data also supported my hypothesis that this phenomenon was caused by habituation. I also found that the time dedicated to anti-predator behaviors differed among urban, rural, and suburban fox squirrel populations in response to coyote and hawk vocalizations. The mean responses to both vocalizations on the rural site (coyote = 45%, hawk = 55%) were at least twice that of those found on the urban sites (coyote = 11%, hawk = 20%). I also used survey responses to questions about squirrel management to test theoretical frameworks linking attitudes to behaviors. My data suggests that beliefs and attitudes that are modified by variables shown to increase accessibility generally correspond better to behaviors. My data also suggests that the inclusion of a measure of previous behaviors will increase the predictive ability of models within different theoretical frameworks. Most importantly for the advancement of a comprehensive theoretical framework, my study showed that composite models combining components of the theory of reasoned action and attitude to behavioral process models out-performed other models.

Thesis (Ph. D.)--University of Oklahoma, 1992. / Includes bibliographical references.

In evaluating a prospective NBA player, one might consider past performance in the player’s previous years of competition. In doing so, a general manager may ask the following questions: Do certain characteristics of a player’s past statistics play a role in how long a player will last in the NBA? In this study, we examine the data from players who entered in the NBA in a five-­‐year period (1997-­‐1998 through 2001-­‐2002 season) by looking at their attributes from their collegiate career to see if they have any effect on their career longevity. We will look at basic statistics take for each of these players, such as field goal percentage, points per game, rebounds per game and assists per game. We aim to use Bayesian survival methods to model these event times, while exploiting the hierarchical nature of the data. We will look at two types of models and perform model diagnostics to determine which of the two we prefer. / text

published_or_final_version / Statistics and Actuarial Science / Doctoral / Doctor of Philosophy