NONADDITIVE EFFECTS OF THE ENVIRONMENT ON THE SURVIVAL OF A LARGE MARINE FISH POPULATION

Climate can affect population dynamics in indirect ways via nonadditive forcing by external variables on internal demographic rates. Current analytical techniques, employed in population ecology, fail to explicitly include nonadditive interactions between internal and external variables, and therefore cannot efficiently address indirect climate effects. Here, we present the results of an analysis, employing specifically developed statistical methodology, on density-dependent survival of walleye pollock (Theragra chalcogramma) prerecruitment stages in relation to background environmental variables in the Gulf of Alaska. We found that spring winds and water temperature mediate the intensity of density-dependent survival from the eggs to the age-0 stage. Fall water temperature and juvenile pollock predator abundance mediate density dependence from the age-0 to the age-1 stage. The inclusion of such nonadditive and nonlinear effects in a population dynamics model improved our ability to simulate pollock recruitment. Our results point to the importance of understanding nonadditive and nonlinear interactions between external (climate) and internal factors in the presence of underlying environmental variation. These topics are discussed in the context of current research priorities in population ecology and conservation biology.