Baldigo, Barry P. 1982. Resource partitioning by sunfish (centrarchidae) populations in an Adirondack lake. M.S. Thesis, SUNY ESF, Syracuse, 94 pp.

Abstract: During the summer of 1979 an investigation was conducted to examine why populations of Lepomis auritus and Lepomis gibbosus were present in an Adirondack lake in such different densities. It was hypothesized that partitioning of the habitat and food resources by the two congeners reduces direct competition for food. Additionally factors other than competition for food were proposed to be responsible, in part, for producing the population sizes.

The respective morphologies of the sunfish facilitated partitioning of the food resource on the basis of size and taxa. Lepomis auritus had a significantly larger mouth and usually consumed larger prey. The pharyngeal teeth of L. gibbosus were more massive than the pharyngeal teeth of L. auritus. The diet of L. gibbosus reflected its morphological distinctions; it often contained gastropods which L. auritus rarely ingested.

The natural diets of the two species of sunfish overlapped least and were most diverse in midsummer, when the food resource base was least dense. High levels of diet overlap and low levels of diet diversity occurred in early and late summer when the resource was most abundant. These results supported the hypothesis of partitioning of the food resource. Isolation enclosure experiments failed to provide concrete conclusions; the results were not significantly different from the results that would occur due to chance or sampling error.

Lepomis auritus had a morphological advantage in acquisition of large prey and in growth rate. And diet overlap was lowest when prey sources could not inhibit population growth and produce the observed differences in population densities. Food partitioning and possible habitat partitioning in conjunction with reproductive superiority of L. gibbosus evidently accounted for population differences. The mean number of eggs per gram of body weight produced by L. gibbosus was found to exceed egg production of L. auritus. Lepomis gibbosus nested at a wider range of depths and substrate types than did L. auritus. The nesting and spawning of L. auritus could have been limited by interspecific and intra specific competition for nesting sites. The spawning flexibility and greater fecundity of L. gibbosus was proposed to provide the most rapid recovery of losses potentially brought about by unstable lake and climatic conditions and was suggested to be a major factor affecting sunfish population sizes in Deer Lake.