Population dynamics of stage-structured sequential hermaphrodites

The population dynamics of sequential hermaphrodites were investigated using three-stage matrix population models. A simple hermaphrodite model with density-dependent reproduction exhibited monotonic asymptotic growth or decline depending on parameter values. After incorporating density-dependent survival and sex change, the model was parameterized for red grouper (Epinephelus morio), which exhibit protogynous life history, and the model was used to investigate the effects of fishing mortality on offspring production and population density. The sensitivity of offspring production to fishing mortality was less when sex change depended on the relative density of female to male (ratio-dependent sex change) or male density alone compared with either female density alone or no density dependence. Although strong ratio-dependent sex change also resulted in less sensitivity of equilibrium abundance to fishing mortality, it caused the population to fluctuate chaotically. This suggests that the strength and type of density dependence on sex change affect reproductive output, equilibrium abundance, and the types of dynamics exhibited.