2.5 The influence of climate change on size of S.
araneus
We examined the weather data from Białowieża from 1952-2004 to explain
changes in skull size in juvenile and adult S. araneus . We
obtained the mean daily temperature (°C), rainfall (mm) and snow cover
(mm) from the Białowieża Meteorological Station. We summed or averaged
these daily measures for longer periods and computed the soil moisture
deficit from monthly temperatures and precipitation using the Watbug
program (Willmott 1977). Monthly deficits were summed for years or other
periods as indicated below. As in the previous section, we used linear
regression, tested for nonlinearity by adding quadratic terms, and
smoothed the relationships with LOESS.
We averaged each of three skull measurements over each year and
regressed averages against weather variables after weighting by sample
size. We calculated the mean daily temperature, sum of the
precipitation, and sum of the moisture deficit in the soil in the period
preceding the collection of specimens (from their approximate time of
birth; see Results for details). We checked for a temporal
autocorrelation (correlation of residuals in neighbouring years) in
juvenile shrews using the Durbin-Watson statistic. To account for the
effect of significant autocorrelation, we corrected the regressions with
the Cochrane-Orcutt procedure. We corrected all regressions using adult
shrews because the smaller sample size (32 years) did not allow us to
test for autocorrelation. The results are shown as the coefficientsr 2, the proportion of the skull size variation
explained by weather variables.