Fitness and implications of reproductive decisions for black brant nesting on the Yukon-Kuskokwim Delta, Alaska.

摘要

Cost of breeding is influenced by numerous decisions during reproduction. In black brant (Branta bernicla nigricans; hereafter brant), an arctic goose, I studied effects of choices individual female brant which influence numerous life history traits.;For birds maintaining long-term monogamous relationships, mate loss might be expected to reduce fitness, either through reduced survival or reduced future reproductive investment. In the second chapter, human harvest of male brant was used as an experiment to examine effects of mate loss on fitness of female brant. Linear mixed models were used to examine variation in clutch size and nest initiation date within individuals relative to treatment (mate loss), number of years delay in breeding following treatment and number of years since resuming breeding. Results indicate substantial fitness costs to females associated with mate loss, but that females which survived and were able to form new pair bonds may have been higher quality than the average female in the population.;Ideal free distribution theory predicts that individuals distribute themselves spatially to produce equal mean fitness across patches. Individual female brant at the Tutakoke River, Alaska, brant colony typically return to the same brood rearing areas across years (Lindberg and Sedinger 1998). Over 21 years, this study found that specific foraging areas consistently produced high quality goslings. Thus, some females consistently reared their broods on areas that produced offspring with low fitness. In this dissertation, I evaluated all components of adult fitness to assess the hypothesis that individuals distribute themselves among seven distinct brood rearing areas in such a way that trade-offs among different life history traits result in equal fitness among areas.;I examined the relationship between brood rearing area rank and future breeding propensity of adult females using these areas. Growth of goslings is known to influence their future fitness. That is, areas where goslings grew most rapidly also produced goslings with the highest mean fitness. We used a multistate robust design approach to estimate the transition probability from a breeding state to a non-breeding (unobserved) state in relation to these measures of quality of brood rearing area. The best supported model allowed the transition from a breeding state to a non-breeding state to be positively related to gosling growth rates across brood rearing areas. These results are consistent with trade-offs by individual brant between fitness of their offspring and their own reproductive value.;The growth period is an important determinant of fitness later in life through its effects on first-year survival and future reproduction. Choices by adult females about where to rear their broods strongly affect growth rates in geese. I explored the potential that gosling growth rates (and associated fitness consequences) are traded off against other vital rates influencing fitness of either adult females or goslings. Growth of goslings primarily influences fitness after fledging, so one hypothesis is that survival before fledging, which is influenced by predation, is traded off against growth rates and post-fledging survival. I estimated pre-fledging and post-fledging survival for goslings reared on areas used by broods.;I used a suite of estimates of vital rates from other studies of this population to estimate brood-rearing-area-specific per capita female recruitment rates (clutch size, apparent nest survival, pre-fledging survival, post-fledging survival, juvenile survival, and breeding probability). I estimated brood-rearing-area-specific adult female annual survival rates which varied among years and areas. I used the sum of brood-rearing-areaspecific per capita recruitment and apparent adult survival to calculate year and brood rearing area specific estimates of lambda. Because I found no variation in lambda among brood-rearing areas and years, adult female brant appear to distribute themselves in an ideal free manner, resulting in equal fitness among females using these areas. It appears that females trade-off among different vital rates during their lifetimes such that individual fitness across habitat patches is equal. (Abstract shortened by UMI.)