Contribution of geographic and environmental distances, and
habitats to beta diversity
We used values of turnover between islands and between cells within
islands to test the effect of geographical and environmental distance on
beta diversity across scales. The analysis were performed using multiple
regression on distance matrices (MRM) with Pearson’s correlation and
10,000 permutations (Lichstein et al., 2007). The MRM were implemented
with the function MRM in ecodist package (Goslee & Urban,
2007). At the intermediate and small scales (between cells within
islands), we also added a third distance matrix to account the effect of
habitats along with the effect of climatic and geographic distance. This
distance matrix was computed as follow: two cells belonging to the same
habitat were coded as 0, and two cells belonging to different habitat
where coded as 1 (following Carvalho & Cardoso, 2014). To determine the
relative contributions of geographical and climatic distance, as well as
habitats, we further used hierarchical variance partitioning to
partition the global R2 into its geographical, and
climatic and habitat components using the function hier.part of
the R package hier.part (MacNally & Walsh 2004). All statistical
analyses were implemented within the R programming environment (R
Development Core Team, 2020).