Short answers, pulled from the story.
An ecosystem is a system formed by organisms interacting with their environment, in which the biotic and abiotic components are linked together through nutrient cycles and energy flows. It consists of all the organisms and the abiotic pools, or physical environment, with which they interact.
The term ecosystem was first used in 1935 in a publication by the British ecologist Arthur Tansley. The word itself was coined by Arthur Roy Clapham, who came up with it at Tansley's request.
External factors, also called state factors, control an ecosystem's overall structure but are not influenced by it, and on broad scales climate is the strongest of these. Internal factors such as decomposition, root competition, shading, disturbance, succession, and the types of species present both control ecosystem processes and are controlled by them.
Resistance is an ecosystem's tendency to remain close to its equilibrium state despite a disturbance. Ecological resilience is its capacity to absorb disturbance and reorganize while undergoing change so as to retain essentially the same function, structure, identity, and feedbacks.
Energy and carbon enter ecosystems through photosynthesis, are incorporated into living tissue, transferred to organisms that feed on living and dead plant matter, and eventually released through respiration. The total photosynthesis by all plants is the gross primary production, and the portion left after plant respiration is the net primary production.
The Millennium Ecosystem Assessment, produced by over 1000 of the world's leading biological scientists, identified four categories of ecosystem services: provisioning, regulating, cultural, and supporting. Of the 24 services it measured, only four had improved over the previous 50 years, 15 were in serious decline, and five were in a precarious condition.
The Hubbard Brook Ecosystem Study, which began in 1963 in the White Mountains of New Hampshire, was the first successful attempt to study an entire watershed as an ecosystem. Its long-term research led to the discovery of acid rain in North America in 1972 and documented the depletion of soil cations, especially calcium.