Factor Analysis of Fish Distribution Patterns in Western and Central Oklahoma

Stevenson, M. M., G. D. Schnell, and R. Black (Department of Zoology and Stovall Museum of Science and History, and College of Education, Education Special Projects [Black], University of Oklahoma, Norman, Oklahoma 73069) 1974. Factor analysis of fish distribution patterns in western and central Oklahoma. Syst. Zool. 23:202-218.-The distribution patterns of western and central Oklahoma fishes were analyzed, utilizing factor analytical techniques, to determine generalized patterns and their correlation with certain environmental variables. Twenty-seven drainage units of the major Arkansas and Red river tributaries were scored for the presence or absence of each of 53 species and values for 13 environmental variables. Six factor groups were obtained through oblique rotation of principal axes that were factored from the correlation matrix of the variables. These six associations were judged biologically meaningful and provide insight into the limiting factors affecting the Oklahoma fish fauna. The relative effects of historical and environmental components on current distribution groupings are discussed and some predictions are made conceming future faunal changes. [Zoogeography; fish distribution; Oklahoma; factor analysis.] Traditionally, zoogeographic studies often have involved the classification of "regions" or grouping of species distribution patterns on the basis of a presupposed explanatory hypothesis. While the conclusions of such an analysis may be correct, it is difficult to effectively evaluate results since the reasoning presented often appears to contain a considerable degree of circularity. However, in Fisher (1968) and Smith and Fisher (1970), this a priori method of creating the ('most plausible grouping patterns" was abandoned. For example, Smith and Fisher (1970) objectively arranged distribution data on Kansas fish species (and environmental data) into a few generalized patterns using factor analysis, and only then were interpretations attempted of the common casual factors affecting each group. We have utilized a similar method to analyze and interpret information on fish distributions in western and central Oklahoma (e.g., west of the 970 meridian). Such an approach should give some insight into the limiting factors which, singularly or in 1 Present address: Tulane University, Systematic and Environmental Biology Laboratory, Environmental Science Center, Route 1, Box 46-B, Belle Chasse, Louisiana 70037. combination, have affected fish distributions in the past, and at least some degree of predictive ability concerning the possible effects of environmental modifications in the future. This rather delimited region was chosen mainly because of the general simplicity of stream type and the relatively complete collections available. We felt it more likely that patterns might be discernable and/or explainable in a relatively uncomplicated environment. The major systems are most often second and third order streams (in the sense of Horton, 1945), with wide flood plains, low relief, sandy bottoms, and a relatively high content of dissolved solids. However, the region also contains a few areas that are major exceptions to this generalization (e.g., the Wichita Mountains). With our analysis, certain generalized patterns of species distributions were discovered which in retrospect are suggested and often predictable on the basis of known ecological requirements of some of the included species. As a working hypothesis, we assumed that one or more of the tested environmental variables would be correlated with and help explain each of the discernable distributional patterns. The co-