You searched for: “ecotone
ecotone (s) (noun), ecotones (pl)
1. In ecology, a transition zone between two distinct habitats that contains species from each area, as well as organisms unique to it.
2. In anthropology, such an area of transition in which certain game or vegetation overlap; a region of primary importance for human subsistence: An ecotone is a transition area between two adjacent ecological communities or ecosystems and it might appear on the ground as a gradual blending of the two communities across a broad area, or it may manifest itself as a sharp boundary line.

Ecotones are particularly significant for mobile animals, as they can exploit more than one set of habitats within a short distance and this can produce an edge effect along the boundary line, with the area displaying a greater than usual diversity of species.

3. Etymology: from Greek, the word was coined from a combination of eco(logy) + -tone, from Greek tonos or "tension"; in other words, a place where "ecologies are in tension".