Drivers of turnover
Each species, of a total of 112 species, was assigned to a dispersal syndrome following the classification of Schaefer et al. (2011). This classification, based on expert criteria, includes five dispersal categories: anemochorous, hydrochorous, endozoochorous, epizoochorous and autochorous (19, 31, 17, 42 and 3 of our species respectively) – the latter being discarded due to the low number of species.
Seventeen climatic variables were obtained from the CIELO model (Azevedo, 1996; Azevedo et al., 1999), corresponding to the WorldClim variables (www.worldclim.org/bioclim) but with a higher resolution for islands (100 x 100 m cell resolution). We checked for autocorrelation among them, and selected the 4 least correlated variables that best represented the different features of climate (Leo et al., 2021): Annual Mean Temperature, Mean Diurnal Range (mean of the monthly difference between maximum and minimum temperatures), Annual Precipitation and Precipitation Seasonality (coefficient of variation). At the large spatial scale, climatic dissimilarity between islands was calculated by averaging Euclidean distance between islands, while at the intermediate and small scale climatic distances were simply the Euclidean distance between the cells. We constructed a global Euclidean distance between all pairs of cells using the four selected climatic variables, which were first standardized with a mean of 0 and unit standard deviation.
For the large spatial scale, we used GoogleEarth® to measure geographical distances in km from coast to coast between all pairs of islands. For the intermediate and small scales, geographical distances between cells were calculated as the distance between the coordinates of the centroids of the cells,