Resource Partitioning in Two Coexisting Sunfish: Pumpkinseed (Lepomis gibbosus) and Northern Longear Sunfish (Lepomis megalotis peltastes)

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Qualitative surveys of 22 lakes in southern Michigan indicated that relative abundances of the northern longear sunfish (Lepomis megalotis peltastes) and pumpkinseed (L. gibbosus) depended upon amount of plant cover and sediment type. The longear sunfish occurred only in lakes with marl sediments and regions of sparse vegetation cover. The pumpkinseed occurred in all lakes surveyed and increased in abundance in lakes with greater vegetation density and/or more organic sediments. Quantitative measurements of habitat and food use were made in five lakes with sympatric populations. Data from underwater transects indicated that large (> 75 mm standard length) longear sunfish occurred primarily in shallow regions containing moderate to low vegetation cover whereas large pumpkinseeds were concentrated in deeper areas with heavy vegetation cover. The smaller size-classes of both species occupied the vegetation in deeper areas of the littoral zone. Large longears consumed predominantly large, sediment-dwelling mayfly or odonate nymphs regardless of the lake or habitat types. Pumpkinseeds consumed mainly gastropods and other prey from the vegetation. Preliminary studies of seasonal food use indicated that the pumpkinseed and longear sunfish both consumed more food in the spring and exhibited greater overlap in diet during this period. The relationship between foraging behaviors of these two species and the types of prey consumed is discussed as well as the complications of assessing competition between species when food and habitat use are dependent on size.Key words: Habitat use, size-class, lake types, food overlap, competition, Lepomis, Michigan