Understanding the ecological and evolutionary links between stages in complex life histories is an important goal of biology, but studies differ greatly in their approach. Some studies follow individuals across their life history ("individual longitudinal"), while others follow cohorts ("cohort longitudinal")—each have their strengths and weaknesses. Our understanding of links among life-history stages probably depends on the approaches we use, but we have no estimates of their relative

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... ce. Using marine invertebrates as a model, we used a formal, systematic literature map to screen 17,000+ papers studying complex life histories. For 3,315 experiments from 1,716 articles, we characterised the study type, (i.e. cohort longitudinal, individual longitudinal or single stage) as well as other factors. Individual longitudinal studies are extremely rare, accounting for just 1.7% of studies. Clearly much progress has been made, but to fully understand the links among life-history stages, more individual longitudinal studies are necessary.