The background similarity test shows that B. thoracicus and B. sonorivox have significantly conserved ecological niches. In both a and b, the y-axis means the frequency of the similarity index (D and I) from 200 random simulations. D and I reflect the extent of niche overlap. The red histogram shows the distribution of similarity index, comparing the actual ecological niche of B. sonorivox with the simulated ecological niche of B. thoracicus. The grey histogram shows the distribution of similarity index in a reversal scenario.