The Use of Surrogate Data in Demographic Population Viability Analysis: A Case Study of California Sea Lions
2015
Reliable data necessary to parameterize
population modelsare seldom available for imperiled species. As an alternative, data from populations of the same species or from ecologically similar species have been used to construct models. In this study, we evaluated the use of demographic data collected at one California sea lion colony (Los Islotes) to predict the population dynamics of the same species from two other colonies (San Jorge and Granito) in the Gulf of California, Mexico, for which demographic data are lacking. To do so, we developed a stochastic demographic age-structured matrix model and conducted a
population viability analysisfor each colony. For the Los Islotes colony we used site-specific pup, juvenile, and adult survival probabilities, as well as
birth ratesfor older females. For the other colonies, we used site-specific pup and juvenile survival probabilities, but used
surrogate datafrom Los Islotes for adult survival probabilities and
birth rates. We assessed these models by comparing simulated retrospective population trajectories to observed population trends based on
count data. The projected population trajectories approximated the observed trends when
surrogate datawere used for one colony but failed to match for a second colony. Our results indicate that species-specific and even region-specific
surrogate datamay lead to erroneous conservation decisions. These results highlight the importance of using population-specific demographic data in assessing extinction risk. When
vital ratesare not available and immediate management actions must be taken, in particular for imperiled species, we recommend the use of
surrogate dataonly when the populations appear to have similar population trends.
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