Variability and Possible Adaptive Significance of Diel Vertical Migration in Calanus Pacificus, a Planktonic Marine Copepod
Adult females of a population of Calanus pacificus inhabiting a temperate fjord, Dabob Bay (Washington), exhibited seasonal and interannual variability in diel vertical migration. This variation was unrelated to food availability, in situ growth rate of females, and thermal stratification of the water column. A model of population growth of C. pacificus, utilizing a life table approach founded on current knowledge of relevant physiological processes, was used to predict growth rates of migratory and nonmigratory populations and to test the implications of several alternative hypotheses for the adaptive significance of diel vertical migration. It was found that hypotheses invoking metabolic advantages for diel migrants (i.e., that diel vertical migration is a foraging strategy optimizing individual growth rate) cannot, even when properly recast in terms of population growth, account for observed migration behavior. Rather, the model suggested a significant causal role for mortality operating differentially on migratory and nonmigratory individuals. The observations of migration behavior in Dabob Bay are consistent with results of the model of population growth, which point unambiguously toward predator avoidance as the major selective advantage of diel vertical migration in C. pacificus.
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Document Type: Research Article
Publication date: 1988-11-01
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