| The central mudminnow and yellow perch are fish species which commonly inhabit small bog lakes. The mudminnow reaches its highest densities in lakes where it is the only fish species. The presence of perch appears to exert a strong negative effect on mudminnow populations. In this dissertation I examine the behavioral interactions behind these population trends (interspecific competition for food and predation) and mechanisms promoting the coexistence of these species (resource partitioning based on microhabitat).; I performed three series of experiments using artificial, liver-baited devices in small aquaria (< 120 l) to simulate six natural foraging sites--open benthic substrate, benthic cover, open water column, submerged aquatic macrophytes, the water's surface, and floating vegetation. Two of these investigations concerned the individual species' use of these sites. In the first, consisting of choice tests involving young-of-the-year perch, fish fed first on midwater items and last on surface and floating vegetation items. These choices agreed with natural perch diets, not with experimentally-derived measures of foraging efficiency, i.e., handling times. In the second experiment, mudminnows displayed comparable foraging rates when using four different foraging sites. This versatility, also reflected in the mudminnow's generalized diet in nature, may aid it in exploiting physically-severe, species-poor environments.; The third foraging site investigation examined the effects of intra- and interspecific competition on the behavior of both species. Intraspecific competition had a greater impact on the foraging success of individual perch than interspecific competition. Mudminnows displayed the opposite pattern. Perch were more efficient forgers than mudminnows on all sites and, in mixed species trials, removed significantly more food items. Interspecific differences in foraging mode contributed to these patterns.; A fourth investigation examined the effects of food patchiness, interspecific competition, and predation on mudminnows foraging in 2,000 l tanks. The food source was trout granules regularly presented at four densities in fixed locations. Mudminnows tended to over-utilize intermediate-quality patches. Mudminnow feeding rates were depressed by small "competitor" perch and large "predator" perch. Foraging patterns were comparable under day and twilight conditions and for small and large mudminnows. |
