MENSURAL DISCRIMINATION BETWEEN SYMPATRIC PEROMYSCUS-LEUCOPUS AND P-MANICULATUS IN SOUTHERN ILLINOIS

A total of 383 Peromyscus was collected from southern Illinois to dete rmine morphological characteristics useful in identifying individuals as either P. leucopus (Rafinesque, 1818) or P. maniculatus (Wagner, 18 45). Polyacrylamide gel electrophoresis of salivary amylase was used t o positively identify all specimens. No univariate morphological chara cter accurately discriminated between the two species because of a hig h degree of intraspecific variation. Stepwise discriminant function an alysis of external characters correctly classified 97.9% of subadults to species. The most important external character was the tail length/ body length ratio. This ratio was also the most important factor in di scrimination of adults; the function correctly classified 98.6% of ind ividuals. Considering skull measurements of adults, 9 cranial characte rs were needed to differentiate between the two species, with a correc t classification of 98.9%. For old adults, all specimens were classifi ed correctly using 5 cranial characters. There was no fast, easy, accu rate method to discriminate between these species 100% of the time in the field.