Ecosystem
The term ecosystem was first used in 1935 in a publication by British ecologist Arthur Tansley. Tansley devised the concept to draw attention to the importance of transfers of materials between organisms and their environment. He later refined the term, describing it as "The whole system, ... including not only the organism-complex, but also the whole complex of physical factors forming what we call the environment". Tansley regarded ecosystems not simply as natural units, but as "mental isolates". Tansley later defined the spatial extent of ecosystems using the term ecotope.
Ecotope
The first definition of ecotope was made by Thorvald Sørensen in 1936. Arthur Tansley picked this definition up in 1939 and elaborated it. He stated that an ecotope is "the particular portion, […], of the physical world that forms a home for the organisms which inhabit it". In 1945 Carl Troll first applied the term to landscape ecology "the smallest spatial object or component of a geographical landscape". Other academics clarified this to suggest that an ecotope is ecologically homogeneous and is the smallest ecological land unit that is relevant.