The demography of Synaptomys cooperi populations in eastern Kansas

Three populations of the southern bog lemming, Synaptomys cooperi, were livetrapped from November 1970 through July 1973 in eastern Kansas to determine whether populations of this microtine species undergo multiannual population cycles. Two of the populations (grids B and D) had such cycles, while one (grid A) exhibited an annual fluctuation in density. The intensity of breeding was generally higher in the summer than in the winter breeding seasons. Grids B and D had a higher percentage of males in breeding condition during two summer breeding seasons compared with grid A. Survival of the trappable adult population was usually higher in the winter than in the summer breeding seasons. Early juvenile survival paralleled changes in survival of the adults but average juvenile survival on grid A was lower than on grids B and D during the summer breeding season. A multiple regression analysis indicated that early juvenile survival is the best predictor of rate of population growth. High body weights in spring were associated with high population densities on grids B and D. Mean body weights of all three populations were higher in the summer than in the winter breeding seasons. Possible mechanisms for the noncyclicity on grid A are discussed.