Population consequences of reproductive decisions.

Behaviour can be a key component of animal population ecology yet the population consequences of behavioural decisions are poorly understood. We conducted a behavioural and demographic study of the bitterling Rhodeus sericeus, a freshwater fish that spawns in live unionid mussels. We used a population model incorporating game theory decisions and measurements of demographic parameters in order to provide predictions of population size among 13 populations of this fish. Our model predicted that the observed behavioural spawning decisions, while maximizing individual fitness, cause a significant 6% reduction in population size compared with randomly distributed spawnings. We discuss our findings in the context of the population consequences of adaptive behaviour.