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 prevalence. 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.

Metabolism sets the pace-of-life, co-varying with survival, growth and reproduction. Metabolic rates should therefore be under strong selection and, if heritable, become less variable over time. Yet intraspecific variation in metabolic rates is ubiquitous, even after accounting for body mass and temperature. Theory predicts variable selection maintains trait variation but field estimates of how selection on metabolism varies are rare. We use a model marine invertebrate to estimate selection on metabolic rates in the wild under different competitive environments. Fitness landscapes varied among environments separated by a few centimetres: interspecific competition selected for higher metabolism, and a faster pace-of-life, relative to competition-free environments. Populations experience a mosaic of competitive regimes; we find metabolism mediates a competition-colonisation trade-off across these regimes. Spatial heterogeneity and the variable selection on metabolic rates that it generates is likely to maintain variation in metabolic rate, despite strong selection in any single environment.