Environmental forcing of life history strategies: Multi-trophic level response at ocean basin scales

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Variation in life history traits of organisms is thought to reflect adaptations to environmental forcing occurring from bottom-up and top-down processes. Such variation occurs not only among, but also within species, indicating demographic plasticity in response to environmental conditions. Between North Atlantic and North Pacific Ocean basins, intraspecific variation in life history traits has been observed among trophic levels from zooplankton to sharks, seabirds, and sea turtles. In all cases examined, species in the Eastern Pacific exhibited later maturation and lower fecundity, but greater annual survival, than conspecifics in the Atlantic. We hypothesize that this dichotomy results from frequency and amplitude shifts in resource availability over varying temporal and spatial scales. Captive studies of fishes have shown that differences in growth and age of reproduction can indeed be a function of environmental control rather than genetic variation. Similar parallel occurrences also have been observed in adjacent seas and between eastern vs. western ocean boundaries. For example, zooplankton and seabird species in cooler North Sea waters exhibit lower fecundity and greater annual survival than conspecifics in the northeast Atlantic and leatherback sea turtles exhibit a larger size and greater reproduction frequency in the Western Pacific vs. Easter Pacific. These examples show system-wide adaptations in life history strategies resulting from environmental 2 forcing and provide a framework for comparisons of ecosystem function among oceanic regions (or regimes) and may prove valuable in modeling ecosystem response to environmental change.