Scholarship & Research
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/1
Browse
2 results
Search Results
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 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.