Predatory Behavior and Competition Among Laboratory-Housed Largemouth and Smallmouth Bass

Abstract

moides) and smallmouth (M. dolomieui) bass were studied in order to document behav.. ioral patterns associated with locating, capturing and ingesting prey, and to evaluate differential responses to a regime of forced competition for limited food. The analyses focused on the behavioral differences associated with (a) different prey species; (b) prey size, and (c) microhabitat. Cinematography aided in the identification of species-specific searching and prey-pursuit behavioral patterns. Both species were able to capture prey using different combinations and sequences of basic functional jaw and head movements. Differences in the relative lengths of jaw bones were not reflected in a difference in the total range of prey sizes consumed by adults of the two species, but rather appeared to affect the efficiency by which various feeding modes were performed (e.g., biting, engulfing and suction). Under the competitive feeding regime, largemouth bass captured significantly higher proportions of large prey and fewer small prey than smallmouth bass in the mixed-species subadult groups. Adult basses exhibited no significant difference in the frequencies of prey captures on the basis of prey size, but did capture prey at significantly different rates from four microhabit/lts in the mixed-species group compared to the conspecific groups. Adult basses of the two species also exhibited significant differences between groups (mixed vs. single species) in the relative proportions of feeding modes used in capturing prey. For each species, there was a significant relationship between the proportions of the feeding modes used and the microhabitats where prey were seized. The microhabitat niche overlap value was 0 = 0.91 for the single species adult groups and 0 =.77 for the mixed-species adult group. Subadult basses did not separate spatially, but rather exhibited lower niche overlap for the prey size dimension in the mixed-species groups (0 =.74), compared to the single species groups (0 = .95). No significant pattern of differential prey captures between bass species was observed on the basis of the five prey species offered. The relationships between morphology, environment foraging efficiency, and behavioral variability are discussed with reference to their potential roles in natural settings.