Theses and Dissertations at Montana State University (MSU)
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Item Variation of life-history strategies in pinnipeds with an emphasis on survival rates and spatial distribution of male Weddell seals in Erebus Bay, Antartica(Montana State University - Bozeman, College of Letters & Science, 2020) Brusa, Jamie Louise; Chairperson, Graduate Committee: Jay J. Rotella; Jay J. Rotella, Robert A. Garrott, J. Terrill Paterson and William A. Link were co-authors of the article, 'Variation of annual apparent survival and detection rates with age, year, and individual identitiy in male Weddell seal (Leptonychotes weddellii) from long-term mark-recapture data' in the journal 'Population ecology' which is contained within this dissertation.; Jay J. Rotella, Katharine M. Banner and Patrick R. Hutchins were co-authors of the article, 'A comparative study evaluating how stage-specific survival rates vary with life-history traits in male pinnipeds' submitted to the journal 'Journal of evolutionary biology' which is contained within this dissertation.; Jay J. Rotella was a co-author of the article, 'Influence of age and individual identity in the use of breeding colony habitat by male Weddell seals (Leptonychotes weddellii) in Erebus Bay, Antarctica' submitted to the journal 'Journal of mammalogy' which is contained within this dissertation.This dissertation explores various components of male life-history theory using a species-specific approach focusing on Weddell seals (chapters 2 and 4) and a comparative approach focusing on pinniped (seal and sea lion) species (chapter 3). To better understand how marine mammal populations can function and to gain insight about the evolution of male Weddell seal fitness, my coauthors and I estimated the age-specific survival rates of male Weddell seals living in Erebus Bay, Antarctica. Actuarial senescence (decreasing age-specific survival with increasing age) has been documented for several wildlife species. However, contrary to females, little information exists regarding age-specific patterns of survival, including actuarial senescence, for males. We used 35 years of mark-recapture data to estimate age-specific survival rates in male Weddell seals using a hierarchical model approach in a Bayesian framework. We found that male survival estimates were moderate for pups and yearlings, highest for 2-yearolds, and gradually declined with age thereafter such that the oldest animals observed had the lowest survival rates of any age, illustrating that male Weddell seals in this population exhibit actuarial senescence. We further investigated male Weddell seal ecology by describing the spatial patterns of male Weddell seals in Erebus Bay using regression modeling and kernel density methods. The intermediately aged males tended to have the most reproductive-age female neighbors, but individual heterogeneity played a stronger role than age. We found that younger males tended to settle in more offshore and less crowded areas of the habitat relative to older males. From a comparative approach, we assessed the patterns of tradeoffs among various fitness traits in male pinnipeds by examining the relationships between stage-specific survival rates and body size, baculum size, mating strategies, and delayed social maturity. Comparative studies similar to ours have tended to focus on females of avian and some terrestrial species and have mostly addressed reproductive traits. However, we lack information about males and connections between survival rates and other life-history traits. We found evidence for a relationship between precopulatory, rather than postcopulatory, traits and survival rates. We highlight the need for more empirical survival rate data and robust comparative methods.Item Investigating diverse sources of variation in the amount of time Weddell seal (Leptonychotes weddellii) pups spend in the water during the lactation period(Montana State University - Bozeman, College of Letters & Science, 2020) Petch, Shane Morgan; Chairperson, Graduate Committee: Jay J. RotellaThe early-developmental period can have important consequences for offspring success later in life. Phenotypic differences among parents and offspring influence energy availability as well as patterns of allocation and trade-offs during development. Variation in behavioral development prior to weaning may be an important determinant of post-weaning success. Here, we use hierarchical Bayesian models and a long-term database of phenotypic characteristics to investigate sources of variation in total time spent in the water and age at first entry in Weddell seal pups from 11-30 days of age. We found that time in the water was greater for pups with higher birth mass, greater for female than for male pups, lower for pups first entering the water at older ages, had a quadratic relationship with maternal age that peaked at intermediate maternal ages, and was higher for pups born to mothers who skipped reproduction the previous year than those born to mothers that were pre-breeders or reproduced the previous year. Some mothers consistently gave birth to pups that spent more time in the water. Age at first entry was earliest for pups with higher birth mass born to mothers with above average reproductive experience. Maternal identity accounted for slight variation in age at first entry. We document that the first entry can occur as early as 4 days old, but on average occurs at age 14 days. Pups born heavier may have more stored energy to allocate to activity or mitigate costs of submergence. Male pups may spend less time in the water to compensate for higher developmental costs. We found support for proxies of maternal body condition but not maternal behavior in describing time in the water, although maternal reproductive experience was supported in our analysis of age at first entry. Our results indicate that some variation in time spent in the water can be explained by the phenotypic characteristics of mothers and pups, though unaccounted-for sources of variation could be involved. It would be useful if future studies would investigate additional sources of variation and seek to understand how time spent in the water is related to post-weaning outcomes.Item Sources of variation in maternal allocation to offspring during lactation in the Weddell seal(Montana State University - Bozeman, College of Letters & Science, 2018) Macdonald, Kaitlin Rose; Chairperson, Graduate Committee: Jay J. RotellaVariation in the allocation of energy to reproduction by mothers can have fitness consequences for mothers and offspring. Diverse features of a mother, and annual environmental fluctuations may affect the amount of energy a mother allocates to offspring and may obscure age-specific patterns that are of interest when evaluating predictions made from existing life history theory. To properly evaluate possible sources of variation, especially age-specific variation in maternal allocation, analyses of data for known-age mothers with a wide range of ages, diverse reproductive histories, and multiple measures of allocation to reproduction are needed. We used data from a long-term study of Weddell seals that were individually marked as pups and monitored annually and a Bayesian hierarchical modeling framework to characterize age-specific variation in maternal allocation and test predictions about age-specific variation while considering additional maternal features that might influence maternal allocation. Based on masses for 311 mothers and associated pups from 2002 to 2016, we found that maternal allocation was moderately associated with maternal age and strongly associated with maternal body mass at birth of her pup. We found that heavier mothers lost a greater proportion of mass during the entire lactation period but that the efficiency with which mothers transferred this mass to their pups was lower than that of lighter individuals. The proportion of mass lost by a mother during the entire lactation period was greater for mothers that had reproduced the previous year and for those who started reproducing young, which suggests that individual quality and perhaps experience are determinants of maternal allocation in this species. Our study did not find support for our predictions that older mothers would allocate more body reserves, be more efficient at transferring mass during early lactation, or alter their behavior in ways that would improve mass transfer efficiency during late lactation, relative to prime-age mothers. The large variation we found in energy allocation to pups translates to large variation in pup weaning mass. Our results highlight that maternal multiple features should be considered when evaluating patterns of age-specific variation in maternal allocation.Item Environmental correlates of reproduction, patterns of maternal allocation, and variation in adult female vital rates in the Weddell seal(Montana State University - Bozeman, College of Letters & Science, 2017) Paterson, John Terrill; Chairperson, Graduate Committee: Jay J. Rotella; Jay J. Rotella, Kevin R. Arrigo and Robert A. Garrott were co-authors of the article, 'Tight coupling of primary production and marine mammal reproduction in the Southern Ocean' in the journal 'Proceedings of the Royal Society B' which is contained within this thesis.; Jay J. Rotella, Jennifer M. Mannas and Robert A. Garrott were co-authors of the article, 'Patterns of age-related change in reproductive effort differ in the prenatal and postnatal periods in a long-lived mammal' in the journal 'Journal of animal ecology' which is contained within this thesis.; Jay J. Rotella, William A. Link and Robert A. Garrott were co-authors of the article, 'Variation in the vital rates of an antarctic marine predator: reproductive costs, age-related changes, and individual heterogeneity' submitted to the journal 'Journal of animal ecology' which is contained within this thesis.The dynamics of populations are the integrated result of multiple processes affecting variation in vital rates. Using a long-term mark-recapture dataset from a population of Weddell seals (Leptonychotes weddellii) in Erebus Bay, Antarctica, I investigated three processes related to population dynamics: environmental correlates of reproduction, sources of variation in maternal allocation to offspring, and sources of variation in the vital rates of adult females. First, I assessed the strength of the association between primary production in the McMurdo Sound and Ross Sea polynyas and the number of pups born in Erebus Bay. I demonstrated both a strong coupling between trophic levels and a surprising timing in the relationship. Pup numbers were most strongly associated with primary production in the months after birth, consistent with a response by mothers to take advantage of the environment of relative abundance. Second, I showed that the patterns of maternal allocation to offspring differ in the prenatal and post-parturition periods. Maternal and pup masses at parturition increased with maternal age (maximum near age 16) prior to declining for older animals, consistent with both restraint and senescence. In contrast, maternal allocation to offspring continued to increase with maternal age during the post-parturition period. Together, these patterns are strong evidence for terminal allocation. Furthermore, I found extensive among-individual heterogeneity, such that some mothers consistently produce heavier pups and allocate more resources during lactation. Finally, I assessed the sources of variation in the vital rates of adult females, using a multistate model to jointly estimate the probabilities of survival and reproduction. Survival rates steadily declined with age, consistent with the onset of senescence at the age of first reproduction, whereas reproductive rates increased for young animals to a maximum 8 years after the age of first reproduction before exhibiting a senescent decline. I found extensive among-individual and yearly variation in reproductive rates, coupled to minimal variation in survival rates. This dissertation adds novel information to the understanding of the complex demography of Weddell seals by revealing an association between trophic levels and patterns of variation in both the allocation of resources to offspring as well as vital rates of adult females. Together, these results shed further light on the flexible life-history patterns of a long-lived marine mammal.Item Investigating the role of dispersal on the genetic structure of wild populations(Montana State University - Bozeman, College of Letters & Science, 2014) Powell, John Henry, III; Chairperson, Graduate Committee: Steven Kalinowski; Steven T. Kalinowski, Mark L. Taper, Jay J. Rotella, and R. A. Garrott were co-authors of the article, 'Estimating inbreeding depression in a non-pedigreed population of Weddell seals Leptonychotes weddellii' submitted to the journal 'Evolution' which is contained within this thesis.; Steven T. Kalinowski, Megan D. Higgs, Michael R. Ebinger, Ninh V. Vu, and Paul C. Cross were co-authors of the article, 'Microsatellites indicate minimal barriers to mule deer Odocoileus hemionus dispersal across Montana, USA' in the journal 'Wildlife biology' which is contained within this thesis.; Steven T. Kalinowski, Megan D. Higgs, and Clint C. Muhlfeld were co-authors of the article, 'Hybridization did not appear to increase dispersal in a westslope cutthroat trout Oncorhynchus clarkii lewisi metapopulation' submitted to the journal 'Canadian journal of fisheries and aquatic sciences' which is contained within this thesis.The movement of individuals among populations (dispersal) is an ecological process that can affect the genes of populations. Identifying the role this process plays in the wild can be difficult due to uncertainty caused by other genetic and ecological processes. Here, I present three studies investigating the role of dispersal in wild populations of Weddell seals (Leptonychotes weddellii), mule deer (Odocoileus hemionus) and westslope cutthroat trout (Oncorhynchus clarkii lewisi). Each of these studies presents, to my knowledge, novel statistical approaches within this discipline that account for the uncertainty caused by other genetic and ecological processes when investigating the role of dispersal. In the second chapter I present a study that uses a two-step maximum likelihood analysis, fit with the data cloning algorithm, to incorporate uncertainty in estimating the probability that an individual has multiple copies of the same gene from a given ancestor into estimates of the association between this probability and the number of pups a female Weddell seal will produce in her life. This study did not find strong support for the hypothesis that increased similarity of an individual's genes reduced the number of pups she would produce across her lifetime. In the third chapter I use individual based genetic distance measures to investigate the association between features of the landscape and the genetic similarity of mule deer. This study found no detectable barriers to dispersal of mule deer across Montana. The fourth chapter presents a study comparing the dispersal rate between samples of westslope cutthroat trout from Glacier National Park that have interbred with introduced rainbow trout (Oncorhynchus mykiss) to samples that have not. There was no detectable difference in the dispersal rate of westslope cutthroat trout that have interbred with introduced rainbow trout relative to those that have not. In conclusion, dispersal is an important ecological process affecting the genes of populations, but understanding the role it plays across a landscape requires adequately accounting for the uncertainty due to other genetic and ecological processes. The three studies presented highlight different ways of addressing this problem when investigating the role of dispersal in the wild.Item Mass estimation of Weddell seals through photogrammetry(Montana State University - Bozeman, College of Letters & Science, 2004) Ireland, Darren Scott; Chairperson, Graduate Committee: Robert GarrottFood resources of pelagic marine predators have traditionally been difficult to monitor and annual monitoring of food-resource availability is not currently feasible for the Weddell seal (Leptonychotes wedellii) population in Erebus Bay, Antarctica. Body mass measurements of parturient females, or their weaned pups, on an annual basis may be used as an indicator of food availability during the previous year and also provide a link between population vital rates and environmental fluctuation. Traditional methods of acquiring mass measurements, including physical restraint and/or chemical immobilization, limit the ability to sample adequately large numbers of individuals from the population of interest. Previous researchers have developed methods to estimate the mass of large seals using scaled photographs, but later application of these methods have not explicitly included uncertainty around estimates derived from predictive equations. I therefore developed the equipment and methods for estimating the mass of Weddell seals using digital photographs and image-analysis software. I then applied the method at a small scale to determine how prediction intervals may be incorporated into calculations based on mass estimates and what affect the explicit use of these intervals would have on the ability to detect differences between the mass of individuals or groups of seals. Scaled photographs of adult female and pup Weddell seals were taken from overhead, ground-level side, and ground-level head or tail perspectives. Morphometric measurements from scaled photographs (photogrammetric measurements) were then correlated using regression against the measured mass at the time of photography. Sampling occurred throughout the nursing period in order to build regression models over a wide range of masses. Resulting regression models predict the mass of adult female seals to within ±13.8% of estimated mass, and ±25.9% of estimated mass for pups. In an application of the method, differences in mass transfer between experienced and inexperienced maternal females and their pups were detected when prediction intervals were explicitly included. Detection of differences between individual seals may not be possible when prediction intervals are included with mass estimates, but estimated mass measurements should be useful for comparing mean differences across a population between years in relation to environmental variation.Item Assessing Weddell seal maternal investment in offspring(Montana State University - Bozeman, College of Letters & Science, 2011) Mannas, Jennifer Michelle; Chairperson, Graduate Committee: Robert A. GarrottReproduction is costly and involves a number of sequential physiological processes that require different levels of energetic investment. In mammalian species gestation and lactation require the most energy and the amount of energy invested in reproduction is reflected in litter size at birth and by offspring growth through weaning. The object of this study was to describe variation in Weddell seal (Leptonychotes weddellii) pup mass at birth and during several ages of the lactation/nursing period, and to evaluate the ability of several maternal traits to explain this variation. Mass measurements were collected from 887 pups at parturition and throughout lactation in Erebus Bay, Antarctica during the 2004 through 2010 field seasons and maternal traits were taken from a long term database. Analysis demonstrated high individual variation in pup mass within a season and modest variation among seasons which suggests that pup mass may be correlated with individual animal attributes rather than annual variation in environmental conditions. Maternal age, a female's reproductive status the previous season and their interaction were found to be the most influential maternal traits. Pup body mass at parturition and during lactation showed maternal age-related variation with evidence of senescence during pre-partum investment and terminal investment during post-partum investment. A female's reproductive status in one season affected her reproductive investment during lactation in consecutive seasons but that effect was correlated with age. Younger females who pupped in consecutive seasons weaned larger pups than those females who were of the same age and did not give birth in consecutive seasons. The opposite was found to be true for older females. The variation in the affect of maternal traits on maternal investment may be due to the increased energy requirement of lactation, age specific changes in reproductive costs, and a senescent decline in physiological function.Item Mass dynamics of Weddell Seals in Erebus Bay, Antarctica(Montana State University - Bozeman, College of Letters & Science, 2008) Proffitt, Kelly Michelle; Chairperson, Graduate Committee: Robert A. Garrott; Jay J. Rotella (co-chair)An individual's body mass is an important life history trait that may vary with environmental conditions and be related to reproductive performance. In this dissertation, we used a 35-year dataset to investigate variations in body mass of Weddell seals (Leptonychotes weddellii) in Erebus Bay, Antarctica with goals of linking environmental conditions, body mass, and reproductive performance. We predicted that variations in environmental conditions and maternal traits would correlate with variations in maternal body mass at parturition, and that variations in maternal body mass may be linked with offspring's body mass and survival probability. We found maternal body mass at parturition showed substantial age- and environmental-related variations. Maternal body mass increased with age through the young and middle ages, and evidence of senescent declines in body mass was found amongst the oldest ages. Additionally, body mass at parturition was strongly influenced by environmental variations during the pregnancy period, specifically body mass was negatively correlated with sea-ice extent and positively correlated with the Southern Oscillation. Annually, pup weaning mass was highly variable. Pup weaning mass was negatively correlated with summer sea-ice extent and positively correlated with summer Southern Oscillation, and these two variables explained 86% of the annual variation in the population average weaning mass. Weaning mass was positively correlated with juvenile survival probability, particularly for males, and we estimated the odds of a male surviving from weaning to age 3 increased 7.3% for every 10 additional kilograms of body mass accrued by weaning. Together, these results suggest large-scale atmospheric-oceanographic variations may affect Weddell seal maternal foraging success and ultimately reproductive performance. Finally, we investigated statistical methodologies accounting for measurement error in photogrammetrically estimated body mass with goals of developing techniques to employ estimated body mass as a covariate in simple linear regression models. We demonstrated that error associated with estimating body mass induces bias in regression statistics and decreases model explanatory power and we described simple statistical techniques accounting for measurement error in covariates. These statistical developments may allow future studies to employ photogrammetric mass estimation techniques and utilize estimated body mass as a covariate in ecological modeling exercises.