What is "wherein clause" modifying?

The results of the niche equivalency showed a significant difference (p < 0.0001) between each clade in a two by two comparison: D. immaculatus–D. suweonensis: D = 0.147, I = 0.417; D. immaculatus–D. flaviventris sp. nov.: D = 0.140, I = 0.354; D. suweonensis–D. flaviventris sp. nov.: D = 0.425, I = 0.714). These results of the niche equivalency tests show that the overlap between clades is less than would be expected by random chance, wherein the absence of difference would assume that two populations are the same species with the same ecological requirements.Yellow sea mediated segregation between North East Asian Dryophytes species

I have no idea what the "wherein" clause is modifying/supplementing.

1.Is this modifying/supplementing "random chance" in front of it? or is this rephrasing the previous sentence (These results of the niche equivalency tests show that the overlap between clades is less than would be expected by random chance)?

2.And is this writer saying the two populations are the same species?

... than would be expected by random chance, wherein the absence of difference ... =

... than would be expected by random chance, in which the absence of difference ... =

... than would be expected by random chance, because, in random chance, the absence of difference ...