Food Restriction: Mechanisms Limiting Numbers and Home Site Utilization in Populations of House Mice, Mus Musculus

Abstract

Although house mouse (Mus musculus L.) numbers have been shown to be reduced by limiting the availability of food, little is known about the mechanisms responsible for limiting numbers or about the effects of low numbers and of variations in the number of feeding points on the way in which the mice utilize the available home sites. In a first experiment, populations inhabiting pens fitted with five home sites were supplied with sufficient food for either 15 or 30 adult mice in five food hoppers. In a second experiment, populations were supplied with sufficient food for 15 mice in either one hopper or in five hoppers. The founding mice in each pen were from one social group and all populations were monitored at monthly intervals for one year. In the pens supplied with sufficient food for either 15 or 30 mice, death rates among the weaned mice were similar to those in pens where food was supplied ad libitum and the numbers of young surviving until weaning matched the numbers dying. With the exception of one pen in which total numbers exceeded the number which could be supported by the available food for several censuses, breeding females were observed at most censuses in all pens and the number of pups born exceeded the number required to replace the mice which died. In all pens most home sites were occupied at all censuses but no site appeared to be the exclusive territory of one mouse or group of mice. In the pens in which the food was supplied in five food hoppers mouse numbers were similar in all home sites but in the pens in which the food was supplied in one hopper mouse numbers were greater in the sites adjacent to the hopper than in those at the other end of the pen. It was concluded that, when food is in short supply, the major mechanism limiting the growth in house mouse populations is high mortality among the pups born into the population. It was also concluded that, when mouse numbers are restricted by the amount of food available, all members of the population share the available shelters rather than establishing separate territories centered on individual shelters.