The influence of age-specific survivorship on pumpkinseed sunfish life histories

Data from five pumpkinseed sunfish (Lepomis gibbosus) populations were used to generate age‐specific survival rates and to test the prediction of life history theory that early maturity and high annual reproductive effort are favored by low adult survival relative to that of juveniles. The prediction relating age‐specific survival to reproductive effort was supported by a strong negative correlation (r = −0.95) between the ratio of adult‐to‐juvenile survivorship and the mean gonadosomatic index of females in the population. The relationship between the adult‐to‐juvenile survival ratio and the mean age at maturity was in the direction predicted by life history theory, but it was not significant. Strong correlations between mean age at maturity and both juvenile growth and the adult‐to‐juvenile growth ratio indicate that growth may affect the timing of maturity more strongly than survivorship in some species.

We estimated the survival cost of reproduction in the populations with the use of demographic data in an optimal life history model developed from the discrete version of the Euler‐Lotka equation. Estimated costs ranged from 5% to 52%, with the two populations exhibiting early maturity, high reproductive allocation, and stunted adult body size displaying the highest survival costs of reproduction in the model. Annual survivorship curves from adults in these two populations showed a marked concavity not illustrated in the other populations, supporting the prediction of life history theory that high reproductive effort results in a high survival cost of reproduction. The selective pressure of a low adult‐to‐juvenile survival ratio appears to favor the evolution of increased reproductive effort in pumpkinseeds, even when this results in the further decline of an already low adult survival rate.