Effect of exploitation on birth, mortality and movement rates in a woodchuck population [Effet de l'exploitation sur la natalité, la mortalité et les taux de déplacement dans une population de marmotte américaine].

Résumé

To assist in understanding the compensatory features of population changes, a detailed examination of the changes in numbers and age composition of a population of woodchucks (Marmota monax) was conducted from l957 to l960 inclusive at the Letterkenny Ordnance Depot near Chambersburg, Pennsylvania. The land is divided into areas of about 600 acres each. Changes in birthrate, mortality rate, and movement in an area from which large numbers of woodchucks were regularly removed were compared with the same kinds of changes in a reference area from which few woodchuks were removed. The voodchucks were captured in box traps that produced an unbiased sample on an age and sex basis but were more efficient in the spring (May). The population was estimated by an efficiency-of-capture procedure. The populations in the two areas remained numerically indistinguishable even though l,040 woodchucks were removed from Area C and only 299 from Area D. The percentage of adults in Area C declined from 70 to 30 but in Area D remained at 70. Survival of young in C increased substantiaIly. The birthrate increased in Area C from l.29 to l.63 and then declined to 0.93in Area D it increased and remained high. Emigration from Area D was much greater than from Area C. Thus, in response to the removal of woodchucks, all three rates changed in directions that compensated for the losses.