Assessing the Effects of Lead Exposure, Environmental Conditions and Metapopulation Processes on Population Dynamics of Spectacled Eiders
Spectacled eider (Somateria fischeri) numbers have declined and they are considered threatened throughout their range. We synthesized the available information for spectacled eiders to construct deterministic, stochastic, and metapopulation models for this species that incorporated current estimates of vital rates such as nest success, adult survival, and the impact of lead poisoning on survival.Abstract
Spectacled eider (Somateria fischeri) numbers have declined and they are considered threatened throughout their range. We synthesized the available information for spectacled eiders to construct deterministic, stochastic, and metapopulation models for this species that incorporated current estimates of vital rates such as nest success, adult survival, and the impact of lead poisoning on survival. Elasticities of our deterministic models suggested that the populations would respond most dramatically to changes in adult female survival and that the reductions in adult female survival related to lead poisoning were locally important. We also examined the sensitivity of the population to changes in lead exposure rates. With the knowledge that some vital rates vary with environmental conditions, we cast stochastic models that mimicked observed variation in productivity. We also used the stochastic model to examine the probability that a specific population will persist for periods of up to 50 years. Elasticity analysis of these models was consistent with that for the deterministic models, with perturbations to adult female survival having the greatest effect on population projections. When used in single population models, demographic data for some localities predicted rapid declines which were inconsistent with our observations in the field. Thus, we constructed a metapopulation model examined the predictions for local sub-populations and the metapopulation over a wide range of dispersal rates. Using the metapopulation model, we were able to simulate the observed stability of local sub-populations, as well as that of the metapopulation. Finally, we developed a global metapopulation model that simulates periodic winter limitation, similar to that which might be experienced in years of heavy sea ice in the central Bering Sea. Our metapopulation analyses suggested that no sub-population is independent and that future management actions may be improved through a metapopulation framework. For example, management actions could include displacement of breeding females from ‘sink’ areas that reduce the growth potential of the population as a whole. However, this action is contingent upon dispersal among local populations, for which there is limited information. Thus, we recommended that researchers examine dispersal behavior among areas on the Yukon-Kuskokwim (Y-K) Delta in western Alaska. The metapopulation framework could also be applied at the rangewide scale to address the density-dependent limitation of available polynya habitat during winter which may limit the recovery of small sub-populations, such as that on the Y-K Delta. Reductions in other sub-populations may be necessary to ensure an increase in the Y-K Delta population. Thus, we recommend that managers consider the inter-population dynamics of spectacled eiders at different spatial scales in future management actions.
Products
Contacts
Flint, Paul L., 907-786-7183Petersen, Margaret R., 907-786-7180
Status: completed
Start Year: 1993
End Year: 2004
Project Sites
Collaborators
FWS - Alaska Migratory Bird ManagementLocation
Yukon Delta National Wildlife RefugeUSGS Mission Area and Program
Ecosystems → Wildlife ProgramMajor Initiatives
FWS - Migratory Bird Management ProgramKeywords
Biological Classification > Animals/Vertebrates > Birds > Ducks/Geese/SwansBiosphere > Terrestrial Ecosystems