Final answer:
Ecosystem engineers are foundation species, often primary producers like kelp, which form the base of their ecosystems, unlike keystone species which maintain biodiversity, or pioneer species which colonize new areas first.
Step-by-step explanation:
Ecosystem engineers, also known as "foundation species," play a critical role in shaping the structure of their environment. They are often primary producers, meaning they can create organic compounds from inorganic substances and are mostly responsible for the introduction of energy into ecological communities. An example of a foundation species is kelp, a type of brown algae, which forms an essential part of the kelp forests off the coast of California. These species are so integral to the ecosystem that their presence maintains the community structure. In contrast, keystone species, like the intertidal sea star Pisaster ochraceus, have an inordinate influence on maintaining biodiversity within their ecosystems, while pioneer species are the first to colonize newly formed land.