DEMOGRAPHY OF A MEDITERRANEAN MICROTINE - THE MEDITERRANEAN PINE VOLE, MICROTUS-DUODECIMCOSTATUS

Microtus duodecimcostatus in a mediterranean vole which is not known t o display spectacular increases in population numbers as in some micro tine species. A population was studied in southern France with a captu re-recapture method. The population included resident adults which hav e a high and constant survival rate (monthly estimate: 0.879), erratic adults (those caught once only), and juveniles which have a lower and constant survival rate. The adult survival rate was not sex-biased bu t the juvenile survival rate was higher in males (monthly estimates: 0 .710 and 0.596 for males and females, respectively). Adult body weight did not vary seasonally. Residents had a higher mean body weight than erratics. Reproduction occurred all the year round. The proportion of reproductive females was higher among residents than among erratics. Population numbers varied seasonally. Our study points out that M. duo decimcostatus is very different from microtine species which display c yclic fluctuations. Population studies on the subgenus Pitymys (which contains M. duodecimcostatus and its closest related species) suggest that they are typically non-cyclic. The importance of social factors i n the control of reproduction and maturation was evidenced in M. pinet orum. The role of such factors in the population regulation of M. duod ecimcostatus is discussed.