Ecotypes sits on the boundary that defines species.
"An analysis of genomic ecotypes by Johannesson, Stankowski, and other researchers explains how some species can maintain the DNA sequences for multiple adaptations, allowing evolutionary processes to effectively select among ecotypes as environmental conditions change — sometimes within only a few generations."
https://www.quantamagazine.org/how-ecotypes-harbor-the-genetic-memory-of-a-species-past-20260521/
