Reproductive value as a key concept in ecology and evolutionary biology.

Reproductive value (RV), originally introduced by Fisher, remains a central concept in population biology. Although most commonly associated with matrix population models, RV has much broader significance because it provides a natural weighting of future contribution within structured biological systems. Whenever individuals, stages, social states, infection classes or habitat patches differ in their influence on long-term population dynamics, RV appears naturally as a common currency for evaluating their contribution to future population trajectories. Here, we synthesise the role of RV across ecology, evolutionary biology, epidemiology and wildlife conservation and management. We examine how RV enters analyses of demographic sensitivities and elasticities, transient population dynamics, life-history evolution, source-sink structure, infectious disease dynamics and the demographic consequences of harvest or environmental perturbation. Whatever the context, the common theme is that present states contribute unequally to future population trajectories. RV also provides a natural link between demography and evolution because it weights the future consequences of survival and reproduction across the life cycle. Traits expressed in individuals or stages with high RV often have disproportionately large effects on population growth, persistence, recovery and fitness-related measures in structured populations. Differences in the distribution of RV among life histories may also contribute to variation in resilience, transient dynamics and responses to environmental disturbance. RV also provides a biologically interpretable basis for conservation and management. Protecting individuals, stages or locations associated with high RV often yields disproportionately large benefits for long-term persistence, whereas harvest or culling directed toward those same classes can strongly depress population growth and recovery. Conversely, management focused on low-RV stages or subpopulations may sometimes reduce demographic impact while maintaining yield or disease control. By linking demographic structure to future population trajectories, RV helps identify the individuals, classes or locations most likely to influence persistence, recovery and management outcomes. Our synthesis highlights why RV repeatedly reappears across diverse areas of population biology. Although RV does not by itself resolve every complexity of ecological or evolutionary dynamics, it provides a powerful framework for understanding how demographic, spatial, evolutionary and epidemiological processes shape the future trajectories of structured populations.