Inbreeding in the field: an experiment on root vole populations

We used a field experiment with replicate populations of a particular geogr aphic race of root voles (Microtus oeconomus) with different degrees of inb reeding to test whether inbreeding effects were expressed in demographic pa rameters. This geographic race had been shown to exhibit reduced reproducti ve rates in the laboratory resulting from inbreeding depression. There were no effects of inbreeding on population growth rate or any demographic para meter. Inbred animals grew less than outbred animals early in the summer, b ut this had no demographic consequences. Our study is one of the few to com pare the performance of the same species in the laboratory and in the field with respect to the extent of inbreeding depression. More such comparisons will be needed to determine whether inbreeding is detrimental more often i n the field than in the laboratory.