The acorn banksia and the cassowary both illustrate a form of this concept mediated through mutualism. Organisms described by this concept typically have low functional redundancy. Robert Paine introduced this concept while studying intertidal rocky zones. Some debate exists as to if ecosystem engineers should be considered a subset of this concept. (15[1])This concept is often illustrated using the sea star (*) Pisaster. Apex predators are typically considered examples of this concept, as their loss can trigger trophic cascades. Sea otters are considered examples of this concept due to protecting kelp forests from sea urchins. For 10 points, name this concept that describes organisms that produce disproportionately large effects on their ecosystems compared to their abundance. ■END■