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A dynamic seascape and a disappearing seal: A biogeographical analysis of the population ecology of the Hawaiian monk seal

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Title: A dynamic seascape and a disappearing seal: A biogeographical analysis of the population ecology of the Hawaiian monk seal
Author: Schmelzer, Isabelle
Department: Department of Zoology
Advisor: Lavigne, D.M.Nudds, T.D.
Abstract: I examined the effect of spatial and temporal environmental variation on Hawaiian monk seal ('Monachus schauinslandi') population dynamics and viability. The Hawaiian monk seal is an endangered species endemic to the Northwestern Hawaiian Islands (NWHI), located in the center of a subtropical gyre, traditionally considered to be unproductive. Recent studies indicate however, that the North Pacific varies both spatially and temporally. Currently, 1300 to 1400 individual seals are distributed among 6 main breeding subpopulations. Marine productivity varied latitudinally throughout the NWHI. Biogeographic regions were identified on the basis of multivariate groupings of environmental data. Monk seal subpopulations located within the same regions varied synchronously over time, while those in different regions did not, a pattern suggesting environmental synchrony. Environmental variation influenced population trends by affecting recruitment of juvenile animals into the adult population. Improved survival was observed for juvenile seals 1-3 years old in productive marine areas, and during El Nin?o events. Pups, buffered by maternal milk, were insensitive to environmental change. The population consequences of ontogenetic and geographic differences in juvenile survival was assessed using stage-structured stochastic models for one subpopulation in each of 3 different marine habitats. Population growth rate was spatially structured such that only the subpopulation located in the most productive area was self-replacing. However, asynchrony among subpopulation growth rates indicates that losses in declining subpopulations may be offset by gains in growing ones. Juvenile survival was found to be a potentially important determinant of monk seal population dynamics, particularly when correlated changes among several age classes occur in response to environmental change. The evidence indicated that the population ecology of Hawaiian monk seals is linked to the NWHI seascape. Consequently, environmental variation may be an important determinant of the potential for recovery of this endangered seal.
Date: 2001
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