What is Ecosystem engineers?

An ecosystem engineer is a species that changes the physical environment for others: beavers flood valleys, earthworms mix and aerate the soil, corals and mussels build reefs, trees cast shade and hold water, elephants open forest into grassland, burrowers oxygenate sediments. Engineers act on the biotope rather than through trophic links, and their effect can outlast them (a beaver meadow, a reef, a peat bog).