Evolutionary ecology of reproduction in Nazca boobies (Sula granti)

The focus of this dissertation is to understand the relationship of two major components of evolutionary ecology (more specifically, life history theory) using Nazca boobies from an island in the Galapagos Archipelago as the model organism for the studies. The dissertation emphasizes the use of flexible and powerful statistical models. More specifically, the focus of these studies is on the costs of reproduction and population sex ratio and sex allocation. A robust theory of life history (i.e., the temporal distribution of major events in organisms' lifetimes from primary stages to natural death) is essential for a complete understanding of evolution via natural selection and adaptation, because natural selection acts on life history traits of individual organisms to establish individual fitness. Separate sexes are associated with sex-specific differences in life history traits, so not only does natural selection act on different life history traits, but it also potentially operates on life history traits differentially depending on the sex of the organism.;The results from the studies presented in this dissertation are consistent with hypotheses of survival and fecundity costs of reproduction. The long-term approach to measuring these costs provided a robust assessment of the influence of environmental variability on survival and fecundity costs. As environmental variability results in decreased resource availability, birds shifted effort from reproductive output to survival. This pattern demonstrates a trade-off between survival and fecundity (i.e., a cost of reproduction). The exploration of the relationship between reproductive costs and population sex ratio presented in this dissertation demonstrates that sex-specific differences in reproductive costs do not explain the observed male-biased operational sex ratio of this population; however, sex-specific differences in resource requirements of nestlings is a likely causal factor for the biased sex ratio.