Fig. 4

Niche of Feirana quadranus and F. taihangnica in environmental space from an ordination technique (PCA-env). In a, b, grey shading shows the density of the occurrences of species by cell. The solid and dashed contour lines illustrate, respectively, 100 and 50% of the available (background) environment. The background area is delimited by the geographic minimum convex polygon with 50-km buffer zone around occurrences of each species. c Represents the contribution of the environmental variables on the first two axes of the PCA and the percentage of inertia explained by the two axes. Histograms in d show the observed niche overlap (D) between the two species (bars with a diamond) and simulated niche overlaps (grey bars) on which tests of niche equivalency and similarity are calculated. The significance of the tests is shown (ns non-significant; **P < 0.05)