Results of ecological niche analyses
Hypervolume analysis indicated that all clades diverge in their niche,
having adapted to largely distinct environmental conditions across their
distribution range (Figure 4). Clade YS had a relatively narrower
ecological niche compared with clade ECS and SCS. The greater niche
differentiation occurs between clade YS and SCS (Table 3), and this is
due to two niche-based operating simultaneously: the most preponderant
is a niche shift, with clade SCS experiencing a wider range of depths
and climatic conditions, and a parallel niche expansion of SCS (or a
contraction of clade YS). The niche of clade ECS, on the other hand,
although disjunct, was more similar to that of the other two clades, as
emphasize by a small distance between centroids. The differentiation of
clade ECS with respect to clades YS and SCS was only due to niche
expansion/contraction processes (Table 3).
TSS and AUC scores showed that all algorithms but surface range envelop
had excellent performance (Figure S4); thus, these nine algorithms were
used to develop the ensemble models. The ensemble SDMs had high
predictive capacity with mean (± standard error) TSS = 0.911 (± 0.003)
and mean AUC = 0.987 (± 0.001). Projections of ensemble SDM suggest that
a large part of coastal areas of China, Japan, and Korea are suitable
for S. schlegeli , which generally matches the current known
distribution range of this species (Figure 5a, Figure S5a). Habitat
suitability projections for this species derived from all three GCMs
showed a clear geographical separation between south and north
populations during the LGM (Figure 5b-d, Figure S5b-d). In addition, SDM
projections suggest that suitable area of S. schlegeli was
greatly reduced during the LGM: the projected distribution area during
the LGM was 10–15% with respect to current depending on the different
GCMs.