Effect of habitat productivity and exploitation on populations with complex life cycles

In this paper we study the consequences of habitat switching and the corresponding ontogenetic diet shifts between adult and juvenile life stages for harvesting and management of exploited populations using a consumer-resource model with stage-specific mortality. Specifically, we study how differences in stage-specific habitat productivity regulate exploited populations and affect yield. We show that the ratio of adult to juvenile habitat productivity determines whether the population is regulated by processes in the juvenile or adult stage and that population responses to changes in mortality (e.g. fishing) or habitat productivity (e.g. eutrophication or physical destruction) depend critically on the mechanism regulating the population. This result has important consequences for the management of marine fish. For example, in fisheries where the exploited population is regulated by processes in the juvenile stage, management measures aimed at protecting the juvenile habitat may be much more effective than regulating fishing effort on the adults. We find also that intermediate differences in habitat productivity lead to alternative stable states between a population regulated by processes in the juvenile or the adult stage. These alternative stable states may lead to counterintuitive population responses to harvestin