8097 - Laserfiche WebLink

Home Browse Search

and between these drainages the frequency of small tributaries is extreme- ly low. Isolation of the two population centers is probably enhanced by this condition. Jordan (1891) is the only one to have recorded the speckled chub from the Arkansas River drainage in Colorado. He found only one individual from near Pueblo, Colorado in 1889. This fact suggests that the speckled chub might not have been historically abundant in Colorado. Three years of intensive sampling failed to find the speckled chub. This species' contemporary range is thought not to extend to Dodge City, Kansas in the Arkansas River drainage (Ken Brunson, personal communication to Charles Loeffler). A probable reason for decline is that the upper por- tions of the Arkansas River in Kansas and Colorado have been severely slow- stressed. For all practical purposes the speckled chub should be consider- ed extirpated from Colorado. Problematical species distributions The Arkansas River Basin may be considered the limit in at least one direction of the geographical range of each of its indigenous fishes. These peripheral populations are often the major source of evolutionary ad- vancement and such populations may be considered as potential resources (Mayr 1963). Biogeography attempts to explain the distribution of species. A speci- fic problem is the explanation of peripherally disjunct or relict distri- butions. In this regard there are three areas of study that can affect which species and how many are found in a particular place: ecology, dis- persal ability and patterns of speciation. The species can be in a partic- ular place because they dispersed there, their ecology permits them to sur- vive or because they speciated there. For the following species I have attempted to marshall existing evi- dence to demonstrate that they are peripherally-isolated, glacial relicts that are native to the Arkansas River drainage in Colorado. Alternative hypotheses are discussed where evidence is equivocal. However, in an analysis such as this, nothing is unequivocal. This is because in attempt- ing to restructure past events, the evidence is of a circumstantial nature based on inferences from the present. Until my discovery of the southern redbelly dace Phoxinus erythro- gaster in Turkey Creek (Pueblo County) in 1979, this species was unknown from Colorado. Some confusion has resulted because Ellis (1914) discussed the occurrence of Chrosomus (~Yhoxinus) erythrogaster dakotensis from the South Platte River drainage of Colorado. This name is now recognized as a synonym of Phoxinus eos northern redbelly dace. The picture of ~. ~. dakotensis on plate IV in Ellis is that of a northern redbelly dace based on the lengths of the snout and mouth. Apparently, Beckman (1952) recog- nized the nomenclatural change and referred to only the northern redbelly dace in Colorado. The presently recognized distribution of this species shows that it does not occur in the upper Arkansas River drainage of Colorado and Kansas (Lee et al. 1980). Disjunct populations in the upper Canadian River (Arkansas River drainage) in New Mexico are considered relictual and native (William Koster, personal communication). 8