The easternmost occurrences of four species are in the area studied. These species are Hybopsis aestivalis tetranemus (Station A-2), Notropis blennius (Station A-1), Notropis girardi (Station A-2), and Fundulus kansae (Station A-2 and Walnut River). These fish are associated with the Arkansas River proper and its sandy western tributaries. In Oklahoma, these fish are found in the Arkansas River as it proceeds eastward and in the downstream portions of some of its tributaries. These fish show little tendency to ascend the streams of the Flint Hills.
SUMMARY
The fish fauna of the area studied is transitional between the Ozarkian and Great Plains faunas.
Fluctuation in water level seemed especially important in determining distribution of fishes in the area studied. Variable climate characteristic of the region studied causes recurrent floods and intermittency in streams. Both of these conditions have probably been accentuated by man's modifications of the habitat. The effects of intermittency were most strikingly demonstrated in small creeks of the uplands. The number of species of fish in the highly intermittent streams was small—especially in the uppermost pools sampled—but the actual number of fish was often high even though the number of species was low. In several instances the only fishes found in these isolated pools were Lepomis cyanellus and Ictalurus melas. This phenomenon of concentrated numbers of individuals of a few species would indicate the presence of limiting factors that allow only those species most tolerant of the particular factor to flourish.
Soon after rains restored flow in these intermittent creeks L. cyanellus and I. melas appeared in parts of the channels that had previously been several miles from the nearest water. Rapid upstream movements of other species after rains was also noted.
It was impossible to ascertain the precise effects of gradient and bottom-type on distribution, but certain species such as Notropis blennius, Notropis girardi, and Fundulus kansae were taken only in streams with sandy bottoms. Notropis deliciosus and Hybognathus placita were most abundant over sandy bottoms.
The high gradient of upland tributaries in the Flint Hills area produced turbulence and bottoms predominantly of rubble. A fauna of which Etheostoma spectabile and Campostoma anomalum were characteristic existed in these waters while they were flowing. As flow decreased and intermittency commenced, qualitative and quantitative changes in the fish faunas were observed. Gradient did not change during drought, but turbulence did. Because turbulence varies with water level as well as gradient, the effect of gradient on fish distribution ultimately is linked to climate.
Probably the small number of fish taken on the Walnut River in comparison with other eastern Kansas rivers (Verdigris, Neosho) results, in part, from the long-term pollution of the stream noted by Clapp (1920:33) and Doze (1924). No percid fishes, black bass, or madtom catfish were taken on the Walnut in Cowley County and the species of Notropis numbered only three.
Four faunal associations seem to be recognizable in the area.