Fig. 4
Long-term (1970–2009) changes in the contributions to total species richness (n = mean number of species per 0.95 m2) of 4 groups of species: a the 10 species of Fig. 2 that showed a statistically significant relationship between winter temperature and number of sites where they were found, b two groups of invaders: (solid points) the 4 exotic species that were newly found in the Wadden Sea and (open points) 5 non-exotic species observed on Balgzand only in recent years, c (solid points) the 6 other species that showed an increasing trend and (open points) the 2 species that showed a decreasing trend in number of sites occupied, d all other 23 species belonging to the list of 50 easily recognizable species. Best linear fits (shown as straight lines in Figure only if statistically significant): a n = −65.6 + 0.035 Y (r = 0.39, n = 40, P = 0.01); b (solid points) n = −93 + 0.047 Y (r = 0.92, n = 40, P < 0.0001), (open points) n = −6.6 + 0.003 y (r = 0.52, n = 40, P < 0.001); c (solid points) n = −89.7 + 0.046 y (r = 0.89, n = 40, P < 0.0001) (open points) n = 19.3–0.0095 Y (r = 0.68, n = 40, P < −0.0001) d n = 12.7–0.001 y (r = −0.02, n = 40, P = 0.9)