Ecological character displacement is phenotypic divergence driven by resource competition. Until now many studies have reported ecological character displacement in various taxa. These studies mainly focused on phenotypic divergence driven by congeneric competition, however reproductive interference which cause reproductive character displacement may occur in congeneric species. Theoretical studies suggested that reproductive interference can cause not only reproductive character displacement but also ecological character displacement. Therefore to evaluate the effect of competition on phenotypic divergence, it is required to evaluate the phenotypic divergence among distantly related species which have no reproductive interference. We focused on phenotypic divergence driven by non-congeneric competition. Amami tip-nosed frog is endangered and endemic in Amami island and Tokunoshima island southern Japan. This frog coexists with non-congeneric potential competitor Otton frog in Amami island while the frog is released from the potential competitor in Tokunoshima island. These islands provide excellent opportunity to examine non-congeneric ecological character displacement. Here, we examined the prediction following the criteria in Schluter (2000) ( (1) phenotypic divergence of Amami tip-nosed frog between these islands, (2) phenotypic change matches ecological shift of prey preference, (3) similarity of potential prey availability between these islands, (4) evidence of competition between these species).
Our result of morphological comparison showed that Tokunoshima island population of Amami tip-nosed frog is significantly larger than Amami island population. Analysis of stomach contents showed that Tokunoshima island population preyed on larger size arthropods than Amami island population did. The prey size preference of Tokunoshima island population is similar to the preference of Otton frog rather than Amami island population. The result of adhesion trap showed that similarity of the arthropods fauna among these islands was high. These results showed that 4 criteria in Schluter (2000) were satisfied. It seems that phenotypic divergence and shift of prey preference in Amami tip-nosed frog occurred despite similarity of prey availability among the islands. Thus we conclude that ecological character displacement in Amami tip-nosed frog occurred by non-congeneric competition which have no reproductive interference.