The correct answer is A. The species which occur abundantly in the ecotone.
An edge species is a species that is found in the ecotone, the boundary between two different ecosystems. Ecotones are often areas of high biodiversity, as they provide a habitat for species from both of the adjacent ecosystems. Edge species are often generalists, meaning that they can tolerate a wide range of environmental conditions. This makes them well-adapted to the changing conditions of the ecotone.
Option B is incorrect, as species on the verge of extinction are not necessarily found in ecotones. In fact, many species on the verge of extinction are found in isolated habitats, such as islands or mountaintops.
Option C is incorrect, as rare species are not necessarily found in ecotones. In fact, many rare species are found in habitats that are not at the boundary between two different ecosystems.
Option D is incorrect, as endemic species are species that are found only in a particular geographic area. Endemic species are not necessarily found in ecotones.