Abstract
We review some patterns of reproduction among and within cohorts of male smallmouth bass Micropterus dolomieu in Nebish Lake, Wisconsin. Previous studies of the population have shown that many males and females fail to breed in a given season and that males are effectively semelparous. Age at first reproduction among males of a cohort appears to be mediated by size, which may in part explain the large number of males failing to breed in a given year. We suggest that competition among cohorts of males result in older males breeding earlier within a season than younger males and that differences in reproductive timing within a season ultimately determine the age at which males of the next generation reproduce. We argue that the observed differences in age at reproduction among males are not alternative life histories, but are the result of a single alternating life history pattern in which males breeding at a young age produce male offspring that breed at an old age and vice versa. The evolution of alternative life histories is not expected because differences in age at reproduction are largely environmentally determined. The high fecundity and large early mortality of fishes make it impractical to directly follow individuals from egg to adulthood, but individual-based computer models should allow us to examine populations for the potential to show such a pattern of life history alternation, and permit us to make precise predictions of consequential population change.
