| Title: |
Relative effects of survival and reproduction on the population dynamics of emperor geese |
| Author(s): |
Schmutz, J., R. Rockwell and M. Petersen |
| Citation: |
J. Wildl. Manage. 61:192-202 |
| Year: |
1997 |
| 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. We constructed an individual-based population model to
evaluate the relative effect of altering mean values of various survival and
reproductive parameters on growth rate 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 growth rate 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 growth rate 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 growth rate, 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 growth rate was
consistent for all 6 parameter sets we examined. The observed variation in
relative effects on growth rate among the 6 parameter sets is indicative of how
relative effects on growth rate may vary among goose populations. With this
knowledge of the relative effects of survival and reproductive parameters on
growth rate, managers can make more informed decisions about which parameters to
influence through management or to target for future study. |
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