A. Sympatric sibling species .B. Sibling species that are members of the same superspecies .3. Hybridization .. A. Intrasped lie hybridization.B. Interspecific hybridization between largely allopatric members of the same superspecies .... C. Limited hybridization between sympatric species not belonging to the same superspecies .4. Evolutionary intermediacy .A. Species polytypic in their North American range .B. Endemic species .C. Species polytypic in their world-wide range .
No takes yet. Share an insight, caveat, or question.
Johnston et al. (1971) studied this question.