Short answers, pulled from the story.
Ecology is the natural science of the relationships among living organisms and their environment. It considers organisms at the individual, population, community, ecosystem, and biosphere levels, studying their abundance, biomass, and distribution. It is a branch of biology that overlaps with biogeography, evolutionary biology, genetics, ethology, and natural history.
The term ecology, written as Oekologie or Okologie, was coined by the German scientist Ernst Haeckel in his 1866 book Generelle Morphologie der Organismen. Haeckel was a zoologist, artist, writer, and later a professor of comparative anatomy. The science of ecology as it is known today began with a group of American botanists in the 1890s.
A keystone species is one connected to a disproportionately large number of other species in the food web, holding lower biomass than the importance of its role would suggest. Its loss causes cascading effects called trophic cascades that can collapse a community. Robert Paine coined the term in 1969, referencing the keystone of an arch, and sea otters limiting kelp-eating urchins are the classic example.
The fundamental niche is the set of environmental conditions under which a species is able to persist, while the realized niche is the set of environmental plus ecological conditions under which a species actually persists. G. Evelyn Hutchinson introduced the modern definition of the niche in 1957, and definitions of niche date back to 1917.
Ecology surged in popular and scientific interest during the environmental movement of the 1960s and 1970s. In 1962, marine biologist and ecologist Rachel Carson's book Silent Spring helped mobilize the movement by alerting the public to toxic pesticides such as DDT bioaccumulating in the environment. Edward O. Wilson predicted in 1992 that the 21st century would be the era of restoration in ecology.
The two main subdisciplines are population ecology, also called community ecology, which focuses on the distribution and abundance of organisms, and ecosystem ecology, which focuses on the fluxes of materials and energy. Ecology has practical applications in conservation biology, wetland management, natural resource management, and human ecology.