Subspecies niche analysis
We used ‘phyloclim’ (Heibl & Calenge, 2018) to quantify the niche
overlap measurements for each pair of conspecific subspecies based on
predictions (Warren et al., 2008): D (Schoener, 1968) andI (van der Vaart, 1998). Both report whether the average
agreement of environmental requirements calculated between subspecies
pairs is greater or smaller than expected if such subspecies were
independent of each other, ranging from zero (no overlap) to one
(identical niches). Then, we assessed the null hypothesis of niche
identity, evaluating the equivalency between pairs of predictions,
comparing the respective observed values of D and Iagainst those generated through 100 pseudoreplicates, assigning the
occurrence points for both subspecies to one lineage or the other at
random to simulate the potential overlap of a group of points occurring
across a given geographic space (Warren et al. 2008).
Moreover, we used background randomization tests to contrast the
observed niche overlap values against a null distribution of 100 overlap
values resulting from contrasting the predictions of one subspecies
against those created from points taken at random from the geographic
space of the another subspecies (Warren et al., 2008). We considered
that: (1) there was niche conservation when the backgrounds overlapped
and niche distance was not significantly different from zero; (2) there
was niche divergence when the distance between both subspecies was
significantly different from zero, independently of backgrounds’
overlap.