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,