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.
Robert T. Paine (zoologist)
In a noteworthy 1966 paper, Paine described a rocky intertidal ecosystem in Makah Bay in Washington State, where top predator species help maintain biodiversity. This led to his 1969 paper in which he proposed the keystone species concept. This concept states that an ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of biomass or productivity. It has become a very popular concept in conservation biology. Paine also coined the term "trophic cascade" to describe the top-down effects that occur in ecosystems when an important species is introduced or removed.