A simple but rigorous graphical method is used to identify optimal strategies in animals in which breeding occurs at a given time (e.g. in a breeding season) irrespective of body size. Under specified assumptions it is shown that larger reproductive propagules (e.g. eggs) should be produced where conditions for juvenile growth are worse. It follows that increased density of juveniles favours larger propagule size under scramble competition for food. For adults two extreme cases are briefly considered, of contest and scramble competition. Increased adult density favours larger size of reproductive propagules and adults if resources are obtained by contest, but not if they are obtained by scramble competition.