Data compilation on magnitude of size changes from literature
We examined publications that report seasonal variation in skull size
and/or brain mass in wild populations of the common shrew (S.
araneus ). From those publications, we additionally used values on total
body mass when reported. For each study, we extracted the percentage of
change from the first summer size peak to the winter minimum (decrease),
and from winter to the second summer peak (regrowth) of each metric.
Whenever estimations of the decrease and regrowth were not directly
reported, we calculated them based on the published data. We determined
the first size peak as the month with the highest mean value for
juveniles; the winter minimum as the month with the lowest mean value
for winter subadults; and the second size peak as the month with highest
mean value for adults. Summer juveniles are immature young individuals
born in late spring or summer; winter subadults are immature
individuals, which are ca. six months old; adults are individuals in
spring and summer which were born the previous year. As S.
araneus has a maximum life span of 13-18 months, there is no overlap of
sexually mature individuals from two generations. When sample size in a
given month was low, we joined data from two or more consecutive months
to determine the corresponding size extreme. The amount of change was
calculated as the difference between mean values in the size extremes.
We added to this data compilation from the literature our own data on
the changes in braincase height, brain mass and/or body mass from four
new populations (see below).
We determined coordinates and altitude for all locations as geographic
variables. We extracted 19 bioclimatic variables from WorldClim Global
Climate Data version 1.4 for all locations (Hijmans et al. , 2005)
and used averaged values from data collected along 1960 - 1990 (see
results section for details).
Following the criteria listed above, we also compiled the same
information on seasonal morphological variation in other wild mammal
species. However, the low number of publications prevented any
statistical analysis.