Annual reproduction patterns in populations of two sympatric species of Peromyscus

Data on annual recruitment patterns were gathered for two sympatric species of Peromyscus: P. leucopus noveboracensis and P. maniculatus gracilis. One-hectare grids were trapped in a mixed deciduous forest in northwestern Massachusetts. Results for all four dependent variables (pregnancy, nonpregnancy, molting, and body weights) indicated a bimodal pattern of recruitment for P. leucopus noveboracensis and a unimodal pattern for P. maniculatus gracilis. Several alternative explanations involving recent sympatry of the two species and possible competition are discussed.