River alteration and niche overlap among three native minnows (Cyprinidae) in the Missouri River hydrosystem
The influence of physical and hydrologic stabilization on habitat niche overlap among three native cyprinid species: flathead chub Platygobio gracilis, sicklefin chub Macrhybopsis meeki and sturgeon chub Macrhybopsis gelida, in riverine segments of the Missouri and Yellowstone Rivers in western North Dakota and eastern Montana, was evaluated. Collectively the three species exhibited higher niche overlap in quasi‐natural river segments than in segments highly altered by a mainstem dam based on relatively high percentages of individuals in quasi‐natural river segments that were classified correctly, according to species, in discriminant function analyses of resource use, compared to lower percentages of individuals classified correctly in the altered river segments. The lower niche overlap in altered river segments resulted primarily from the lower overlap between flathead chub and the remaining species; this appears to be related to a decline in the diversity of natural habitats and conditions that provided a wide range of habitat conditions suitable for all three species. Results from this study suggest that selective segregation and habitat changes, rather than interactive segregation and competition, is probably the mechanism responsible for the pattern of habitat use and niche overlap among the three species in the altered segments.
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