Temperature affinity over time
The mean ruderal community temperature index (expressed as mean EIV-T
value per subregion per time step) was higher in historical records than
in recent times. For total ruderal species, there was a significant
interactive effect of the observational year and subregion (Fig. 3a,
supplementary Table 3), with mostly lowest EIV-Ts in general observed in
1983 (2.2 ± 0.2) and highest in 1903 (3.3 ± 0.1) and 1913 (3.3 ± 0.1).
Mean EIV-Ts were constant within subregions between observational years,
except for 1983, which showed the most variation in these values. The
mean community temperature index for non-native ruderal species
decreased gradually through time, without an interactive effect of
subregion (Fig. 3b, supplementary Table 4). Similar negative trends
occurred for the mean community temperature indices as a function of the
first year of observation in a subregion (Fig. 3c-d, supplementary
Tables 5-6). In combination with the high degree of heterogeneity that
existed between communities (supplementary Fig. 4), this suggests that
newly introduced species (in 1983 and 2021) were less warm adapted than
in 1903-13.