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Relationships of the Topminnows Fundulus notatus and Fundulus olivaceus in the Upper Mississippi River Valley
Marvin E. Braasch and Philip W. Smith
Vol. 1965, No. 1 (Mar. 18, 1965), pp. 46-53
Stable URL: http://www.jstor.org/stable/1441238
Page Count: 8
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In the upper Mississippi River valley, Fundulus notatus and F. olivaceus differ markedly in pattern and size, slightly in scale and ray counts and in proportions. These species tend to be microgeographically and ecologically separated, with notatus occurring in low-gradient streams and sloughs in relatively level areas, and olivaceus in fast, gravelly streams in upland areas. They have occurred together for 60 years or more in several stream systems in southern Illinois, and comparison of allopatric and sympatric samples suggests some character displacement. The more northern notatus is unable to penetrate the range of olivaceus in highlands but does so along the broad Mississippi River floodplain.