Demography of California sea lion colonies in the Gulf of California, Mexico.

摘要

Populations of animals in which individuals of different age, size, or other life history attributes differ in their contribution to population growth are considered structured populations. Models for structured populations require the use of attribute-specific demographic rates to accurately assess conservation status. Unfortunately, reliable vital rates are seldom available for long-lived species, especially rare species of conservation concern. When scientists are unable to estimate vital rates, surrogate demographic data are frequently used to model population dynamics and identify conservation priorities. However, this practice may influence the predictive accuracy of population models because the target species may not respond to environmental conditions or human stressors as surrogates do.;In this dissertation, age- and sex-specific survival and birth rates for a long-lived pinniped, the California sea lion (Zalophus californianus ) of the Gulf of California, Mexico, are estimated. This study also evaluates the utility of these data for predicting the dynamics of other populations of the same species for which few demographic data are available. Age-specific birth rates are estimated from the reproductive histories of animals branded at the Los Islotes colony (LI). Using the same resighting history, age- and sex-specific annual survival probabilities are estimated using mark-recapture models. Age- and sex-specific survival probabilities are then estimated for pup and juvenile California sea lions from three colonies in the Gulf of California: LI, San Jorge (SJ), and Granito (G). A stochastic demographic population viability analysis is presented for each population using the respective pup and juvenile survival probabilities and surrogate data (adult rates from LI and San Miguel island, California) for Si and G. The population trends predicted by the demographic model are compared to the observed population trajectories for each colony obtained from 24 years of census data.;This study shows that age-specific birth rates vary among age classes, while apparent survival rates vary for different age- and sex-classes. Only pup survival varies by year. The use of surrogate data to predict population trends of the same species may yield misleading information and should be used with caution in deciding conservation plans.