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.