Data from: Lower body mass and higher metabolic rate enhance winter survival in root voles, Microtus oeconomus

Although the biological significance of individual variation in
physiological traits is widely recognized, studies of their association
with fitness in wild populations are surprisingly scarce. We investigated
the effect of individual phenotypic variation in body mass, resting (RMR)
and peak metabolic rates (PMR) on mortality of the root vole Microtus
oeconomus. Body mass and metabolic rates varied significantly among
consecutive years and were also age dependent, as individuals born in late
summer and autumn were characterized by significantly lower body mass and
metabolic rates than animals born earlier. At the beginning of winter
voles born in spring and early summer exhibited reduced body mass and
metabolic rates, whereas animals born later maintained lower body mass and
RMR, which may be interpreted as phenotypic plasticity enhancing the
probability of survival. Body mass had no significant effect on vole
survival during summer. In contrast, smaller individuals were
characterized by lower mortality during early winter, whereas higher body
mass was positively associated with survival later in the season. High
body-mass-corrected RMR positively affected survival in both summer and
winter. The effect of PMR was apparent only during winter, though its
direction (and correlation with RMR) varied among years. Deep snow cover
negatively affected the survival of voles in both early and late winter.
Ambient temperature was positively associated with winter survival, except
for late winter, when rising temperature caused flooding of vole habitat.
We conclude that the lack of consistency in the directionality and
strength of the effects of body mass and metabolic rates on winter
survival does not undermine their importance, but rather demonstrates the
ability of individuals to adjust metabolic rate to changing environmental
conditions.