Manipulation of offspring number and size: benefits of large body size at birth depend upon the rearing environment

Summary 1. Allocation of reproductive effort between the number and size of offspring determines the immediate rearing environment for the growing young. As the number of offspring increases, the amount of parental investment per individual offspring decreases, and the quality of the rearing environment is expected to decrease. This may result in a lower quality of offspring reared in such conditions. 2. We studied the effects of the rearing environment on the quality of juvenile bank voles, Clethrionomys glareolus , with different initial body sizes at birth in a 2 〈 2 factorial experiment. The rearing environment was manipulated by enlarging both the litter size by two extra pups, and mea…