Relative effects of survival and reproduction on the population dynamics of emperor geese

Authored by RF Rockwell, JA Schmutz, MR Petersen

Date Published: 1997

DOI: 10.2307/3802428

Sponsors: No sponsors listed

Platforms: No platforms listed

Model Documentation: Other Narrative Mathematical description

Model Code URLs: Model code not found

Abstract

Populations of emperor geese (Chen canagica) in Alaska declined sometime between the mid-1960s and the mid-1980s and have increased little since. To promote recovery of this species to former levels, managers need to know how much their perturbations of survival and/or reproduction would affect population growth rate (lambda). We constructed an individual-based population model to evaluate the relative effect of altering mean values of various survival and reproductive parameters on lambda and fall age structure (AS, defined as the proportion of juv), assuming additive rather than compensatory relations among parameters. Altering survival of adults had markedly greater relative effects on lambda than did equally proportionate changes in either juvenile survival or reproductive parameters. We found the opposite pattern for relative effects on AS. Due to concerns about bias in the initial parameter estimates used in our model, we used 5 additional sets of parameter estimates with this model structure. We found that estimates of survival based on aerial survey data gathered each fall resulted in models that corresponded more closely to independent estimates of lambda than did models that used mark-recapture estimates of survival. This disparity suggests that mark-recapture estimates of survival are biased low. To further explore how parameter estimates affected estimates of lambda, we used values of survival and reproduction found in other goose species, and we examined the effect of an hypothesized correlation between an individual's clutch size and the subsequent survival of her young. The rank order of parameters in their relative effects on lambda was consistent for all 6 parameter sets we examined. The observed variation in relative effects on lambda among the 6 parameter sets is indicative of how relative effects on lambda may vary among goose populations. With this knowledge of the relative effects of survival and reproductive parameters on lambda, managers can make more informed decisions about which parameters to influence through management or to target for future study.

Tags

models ecology growth Rates Black brant Fecundity Lesser snow geese Canada geese