Latitudinal Growth Effects on Predator-Prey Interactions between Largemouth Bass and Bluegills in Ponds

Abstract

Record weights of largemouth bass (Micropterus salmoides) exhibited a significant (P ≲ 0.05) inverse relationship to latitude throughout the Great Plains states. However, bluegill (Lepomis macrochirus) record weights from the same states exhibited no significant difference (P [>] 0.05). When northern (Montana) and southern (Oklahoma) populations of adult largemouth bass and bluegills were modeled in relation to geographical growth rates, longevity, and constant annual mortality, similar latitudinal relationships existed. Northern largemouth bass grew slower and failed to reach the maximum sizes attained by southern largemouth bass. The Proportional Stock Density value was 12 for the modeled northern largemouth bass population, while the southern largemouth bass population had a value of 50. Northern bluegills also exhibited lower growth rates than southern bluegills; however, the difference in maximum size was slight. The Proportional Stock Density value was 10 for the modeled northern bluegill population, while the southern bluegill population exhibited a value of 23. Analyses of modeled population structures indicated a greater reduction in the absolute sizes of predators on a latitudinal gradient than occurred among prey. This variation in the relationship between the sizes of predator and prey would have a distinct effect on prey vulnerability. Simulated adult bluegill populations in southern latitudes were nearly twice as vulnerable to largemouth bass predation as bluegills in northern ponds. Therefore, bluegill recruitment would seem to be more subject to natural control at southern latitudes.