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.