An edge species is a species that is well adapted to the increased variety of resources and unique habitat complexity found in ecotones (i.e., the interfaces of different ecosystems), including with regard to light, moisture, vegetation structure and species mixtures.
The meaning is very different from EDGE species (Evolutionarily Distinct and Globally Endangered species), which refers to species that are both genetically unique and at risk of extinction and which have thus become foci of conservation efforts.
Many amphibian species, including frogs and salamanders, are edge species because of their need to access both aquatic and terrestrial habitats for breeding and feeding. Likewise, some species of birds, rabbits and deer utilize both forests and open land for breeding, feeding and shelter.