Effect of Predators on Growth and Reproductive Investment in Bluegills: Comparison of Populations with Differing Size and Age of Maturation

Growth rate and age of maturation are two important factors that control adult body size. Predators can also exert an influence on the size and age of maturation of their prey. We compared the growth, timing of maturation, and investment in gonad development of bluegills Lepomis macrochirus in ponds with and without largemouth bass Micropterus salmoides predators. In addition, we compared the response between bluegills from stunted (small size and early age of maturation) and nonstunted (larger size and later age of maturation) populations to determine whether predation could explain the occurrence of stunted body size in bluegills. For both males and females, we found that bluegills grew faster but matured at the same rate in the presence of predators. The investment in gonad development (measured by the gonadosomatic index) did not differ between individuals raised with predators and those raised without. Regardless of predator treatment, fish from the nonstunted population grew more than those from the stunted population and invested less energy in gonad development. The interaction between population source and predator presence was not significant, suggesting that the observed predator responses did not differ between bluegills from the stunted and nonstunted populations. These results support the hypothesis that predators have a strong influence on the life history of the bluegill. Bluegills grew more in the presence of predators, but this did not result in a corresponding reduction in the investment in reproduction.