Population consequences of reproductive decisions

Behaviour can be a key component of animal population ecology yet the popul ation consequences of behavioural decisions are poorly understood. We condu cted a behavioural and demographic study of the bitterling Rhodeus sericeus , a freshwater fish that spawns in live unionid mussels. We used a populati on model incorporating game theory decisions and measurements of demographi c parameters in order to provide predictions of population size among 13 po pulations of this fish. Our model predicted that the observed behavioural s pawning decisions, while maximizing individual fitness, cause a significant 6% reduction in population size compared with randomly distributed spawnin gs. We discuss our findings in the context of the population consequences o f adaptive behaviour.