The distributions of groups (2) and (3) provide clues to the effect of drought on the fish-population, and on the relative ability of various species to repopulate areas where they have been extirpated.
Larimore et al. (1959) studied the re-establishment of stream-fish following drought in Smiths Branch, a small warmwater stream in Illinois. They found that 21 of the 29 species regularly occurring there reinvaded most of the stream-course within two weeks after the resumption of normal flow, and that all but three species were present by the end of the first summer. Our study indicates a much slower rate of dispersal by many of the same species. This is presumably attributable to the ecological barrier presented by the Wakarusa mainstream.
During the drought (1952-1956) the mainstream with its turbid water and mud bottom could hardly have served as a refugium for species requiring the clear water and gravel bottom of upland tributaries. Probably the main refugia for these species [group (3)] were in the upper portions of Rock Creek, Washington Creek and possibly Deer Creek. While collecting we observed that these creeks had larger proportions of gravel-rubble bottom, clearer water, deeper pools, and appeared to be more stable than other creeks in the drainage. In Washington Creek, Lone Star Lake enhanced stability of flow.
At the end of the drought, fishes in group (3) probably were extirpated or decimated in other tributaries of the Wakarusa. After normal flow recommenced in 1956, fishes re-entered the previously uninhabitable streams or stream-segments. The rate of redispersal by various species probably depended upon their innate mobility, and upon their tolerance of the muddy mainstream of the Wakarusa.
Our observations suggest that certain species in group (3) dispersed rapidly from refugia in Rock Creek, Washington Creek, and possibly Deer Creek. These species may, of course, have survived in a few remaining pools in tributaries throughout the basin, thereby necessitating only minor redispersal within these tributaries following drought.
Species of group (3) that were most tolerant of drought or that dispersed most rapidly are Catostomus commersonnii, Notropis umbratilis, Pimephales notatus, and Percina caprodes; these were present in the uppermost portions of the basin in 1959. Fishes having lesser capacity for survival or dispersal are Semotilus atromaculatus, Notropis topeka, Phenacobius mirabilis and Campostoma anomalum; in 1959, they were not found farther upstream than Burys Creek. Etheostoma spectabile, the orangethroat darter, was taken in Rock Creek, Washington Creek, Deer Creek, Strowbridge Creek, Elk Creek, and at station 24 on the Wakarusa. This is a riffle-dwelling, comparatively sedentary fish, not a strong swimmer. These traits, coupled with the long, muddy pools and infrequent riffles of the Wakarusa mainstream, provide a reasonable explanation of the comparatively slow rate of dispersal by the orangethroat darter.
Several species showed no tendency for redispersal following drought, in that they were confined to Washington Creek or Rock Creek in 1959. Noturus exilis was taken only in Washington Creek immediately below Lone Star Lake. Rock Creek is the last stream in the Wakarusa Basin in which Notropis cornutus, Hybopsis biguttata and Etheostoma nigrum have survived. These species require comparatively permanent streams having pool-and-riffle habitats and gravelly bottoms for spawning. Hybopsis biguttata has been recorded only from Rock Creek, where it was last taken in 1924. It is interesting to note that this species had not reinvaded Smiths Branch, in Illinois, three years after the resumption of stream-flow (Larimore et al., 1959). Notropis cornutus and Etheostoma nigrum, although formerly more widespread in the Wakarusa Basin, have been taken recently only in Rock Creek.
Faunal changes that have occurred in the basin in the past 60 years indicate a decrease in extent of clear, continuously flowing stream-habitat.
Comparisons with Faunas of Nearby Streams
Minckley (1959) reported 13 species from the Big Blue River Basin that were not taken in our survey of the Wakarusa. Most of the 13 are fishes that probably occur throughout the lower mainstream of the Kansas River and might enter the lower Wakarusa occasionally. Chrosomus erythrogaster and Notropis rubellus were reported by Minckley but have not been found in the Kansas River Basin east of the Flint Hills, either in recent or in early collections. On the other hand, five species have been reported from the Wakarusa but not from the Big Blue River. Two of these, Notemigonus crysoleucas and Chaenobryttus gulosus, may have been introduced by man. The remaining three, Hybopsis biguttata, Noturus exilis and Percina caprodes, have not been taken farther west than Mill Creek, Wabaunsee County. In general the faunas of the two systems are similar; forty species are common to both.