3.2. Climate niche divergence/conservatism
The initial two axes of PCA accounted for 45.44% and 23.16% of the
total variance, respectively. The climate niche overlap between the two
species was relatively low, with
Schoener’s D value being 0.30.
Notably, the outcomes of the niche equivalency test, as depicted in Fig.
5, revealed that the actual
overlap value was significantly higher (Schoener’s D) compared to the
simulated niche (P
< 0.009 ). This suggests that the similarity in climate niches
between the two species is more pronounced than what would be expected
by random chance. Furthermore, as per the niche similarity test, the
observed niche overlap did not exhibit a significant increase compared
to what would be anticipated based on the environmental conditions
available to each species in both directions (P
(1->2) < 0.07, P (2->1) <
0.06 ). When calculating climatic niche dynamic indices, which indicate
niche shifts in similar conditions, it becomes evident that there is a
high degree of niche stability at 96%. Additionally, the degree of
niche unfilling stands at a moderate 43%, while niche expansion is
notably low at 3%.
A comprehensive analysis of climatic niche quantitative tests
underscores that Z. spina-christi and Z. nummulariaexhibit limited overlap (Schoener’s D = 30%) (Broennimann et al., 2012;
Ahmad et al., 2019; Datta et al., 2019; Xian et al., 2023) (as
illustrated in Fig. 5 and detailed in Table 5).