Prediction of the Maxent distribution
We choose the best model and find the corresponding RM and FCs
parameters for Maxent model to facilitate increased rigour in the
development of Maxent models (Table 2). Finally, the distributions based
on Maxent across S. boulengeri clades were characterized by high
AUC statistics, indicating that these ENMs successfully discriminated
real occurrences from background locations. Jackknife tests on variable
importance for S. boulengeri clades revealed that Precipitation
of driest month in E. A, E. B and W. a clades, while Annual
precipitation in E. C and E. D and Annual mean temperature in W. b
produced the greatest decrease in gain when excluded from the model,
suggesting these climate factors limit distributions of clades
correspondingly, which likely to be the most important reasons for the
next step niche divergence.
Hypothesis
tests based on ENMs and PCA-env approaches
ENMs based niche equivalency tests reveal that 4 paired comparisons do
not reject null distributions, seem equivalent as the values of observed
niche overlap fall well in the middle of the null distributions
(Supplementary material Appendix Figure A1). ENMs based background
similarity tests indicate greater niche divergence between pairwise
comparisons (2/15): E. B vs. W. b and E. A vs. E. B (Supplementary
material Appendix Figure A2a, A2i). Interestingly, some pairwise
comparisons (7/15) just show one-side significant divergence. The last
part (6/15) niche overlap falls within the 95% confidence limits of the
null distributions, leading to non-rejection of the hypothesis of
retained niche conservatism.
The results of PCA-env based niche equivalency test (Figure 3d, 3e and
Supplementary material Appendix Figure A3) show that pairwise
comparisons of 80% (12/15) less than expected null distribution ranges
and reject null hypotheses, indicating closely related clades are not
equivalent to most related clades, and most clades have undergone
significant alteration of their environmental niche and clades may be
more resilient to climate changes than their native ranges suggest.
Niche background test indicates that 11 paired comparisons show a very
limited niche overlapping values (scores < 0.3). Only 4 paired
comparisons show niche overlap categorized as a moderate overlap
(0.307–0.527). On the other hand, the background similarity tests
indicate generally little niche similarity among the pairwise
comparisons in six clades (Table 3 and Supplementary material Appendix
Figure A4). The ordination null tests of niche similarity show that
niches are less similar than random expectations in 30% (5 paired
comparison cases) in reciprocal directions, while 26% (4 paired
comparisons) are significantly not to reject the null hypothesis of
niche conservatism in bi-directions.