THE GROWTH OF CONFINED COLONIES OF THE WILD HOUSE‐MOUSE (MUS MUSCULUS L.): THE EFFECT OF DISPERSAL ON FEMALE FECUNDITY

Abstract

SUMMARY Post‐mortem examination of female house mice from a confined population showed a higher proportion of non‐fecund females than would be found in a wild‐caught sample of similar age composition. A similar population was allowed to disperse into a larger pen, whereupon the reproductive rate increased. The result was not clear‐cut, however, as the increase began too soon to be attributable to dispersal alone. Another similar population was divided into two colonies of unequal size. Non‐fecund females transferred to a new large pen with few other mice became fecund and reproduced successfully, while those placed in a new small crowded pen remained non‐fecund. A completely adult population in which no litters had been born for over six months was allowed to disperse into a large pen. A majority of females became fecund and conceived within about one week. The numbers were doubled within eight weeks. The results suggest the existence of a self‐regulatory mechanism, which operates at population densities seldom, if ever, reached in free‐living populations.