Age and size at first reproduction of fishes: Predictive models based onlyon growth trajectories

Age and size at first reproduction have broad implications for studying pop ulation and community ecology. From general functions of body growth we dev eloped models for estimating both age and size at first reproduction when g rowth trajectories are the only reliable information. We evaluated our mode ls using empirical data, including 85 species of marine and freshwater fish es, with 235 populations or sex groups. From the data set, we found the fol lowing two sets of relations. (1) There is a nonlinear negative relation be tween the von Bertalanffy growth coefficient (K) and the age at first repro duction (T-r). (2) The ratio of body length at first reproduction (L-r) to asymptotic body length (L-inf) may increase in two possible ways: one is in creases in K and, consequently, decreases in L-inf; the other is increases in T-r and delay of the age at first reproduction. Our model integrates the above complex relations into a simple linear function. The set of life-his tory invariants summarized by E. Charnov and by A. L. Jensen is a special c ase of our model. The pattern of life-history diversification demonstrated by K. O. Winemiller and K. A. Rose is similar to our model implication and the results of our data analysis. Additional information about other comple x traits such as mortality and fecundity are not needed in our models, so o ur models provide an independent basis for testing life-history theories an d for applying those theories to modeling population dynamics.