The Effect of Flexible Growth Rates on Optimal Sizes and Development Times in a Seasonal Environment

The interrelationships among development time, growth rate, and adult size are investigated using simple optimization models of a seasonal life history in which larger adults have greater reproductive output. Unlike most previous studies, our models assume that growth rate is an adaptively flexible character that can be increased at the expense of a greater juvenile mortality rate. Three components of fitness are considered: the cost of developing at a suboptimal time of the year, the reproductive advantage of larger adult size, and the increased mortality from rapid juvenile growth. The study focuses on the optimal responses of size, development time, and growth rate to changes in the amount of time available for completion of the life cycle. The models show that the optimal growth rate and size at maturity may respond in several different ways. Perhaps the most likely effect is that growth becomes faster and size smaller with less time available. It is also possible, however, for either growth rate or size (but not both) to stay constant; in other cases, less time available leads to slower growth or larger size. The effects of increased mortality on the juvenile stage are also explored; here, the optimal size is likely to decrease, but growth rate and development time may increase or decrease.