Adult Sex Ratio as a Demographic Feedback Linking Mating Systems, Parental Care, and Evolution

Behavioral ecology is shifting from static models of sex-role evolution to dynamic frameworks in which demography and behavior form coupled feedback systems. Here, we outline a unifying approach developed at the University of Bath-the demographic feedback model-that links individual decisions to population structure through the adult sex ratio (ASR), a measurable demographic variable that integrates survival, maturation, and reproduction. Across species, sex-biased survival and remating opportunities generate a recursive feedback between mating systems, parental care, and sexual dimorphism. This feedback, in turn, shape population viability and conservation outcomes. By embedding ASR monitoring within long-term field studies and comparative phylogenetic analyses, our research reveals how demographic distortions propagate through social behavior, and how behavior feeds back to restructure demography. The resulting feedback framework connects behavioral ecology, life-history theory, and conservation demography under a single logic: populations evolve not through linear causation, but through nested feedbacks linking genes, ecology, and behavior. We identify four key frontiers-cross-taxon field protocols, causal comparative inference, nested-feedback theoretical modelling, and integration with biodiversity conservation practice-that will define the next generation of research. Recognizing behavior as both a product and a driver of demographic structure opens a path toward a genuinely recursive theory of evolution.