Body mass dynamics in the Mediterranean pine vole Microtus duodecimcostatus



The occurrence of large individuals in fluctuating populations of microtine rodents (the Chitty effect) has received considerable attention. Recent studies showed that there are no causal relationships between the Chitty effect and the multi-annual population cycles of voles and lemmings. We studied five populations of Microtus duodecimcostatus in southern France with capture-recapture methods. Mean body mass was constant in all populations. Maximum observed body mass was more variable, and slightly positively correlated with density, except in the most fluctuating population where the correlation was strong. A careful study of the occurrence of large voles in these populations showed that most were pregnant females, and that the few large males were present when density was high and sample sizes were large. Comparison with published studies indicates that the Chitty effect, though not restricted to microtines, is not a general phenomenon in small mammal populations. Our field results and laboratory data on the same species suggest that M. duodecimcostatus has a determinate body growth, contrary to some Microtus species which have an indeterminate growth.