A species so critical to an ecosystem that its removal could potentially destroy the entire system. A good example of this are Blue Jays, which plant acorns that give rise to oak forests. Without Blue Jays, oak forests are not naturally replenished and without the forests, all other species in the ecosystem cannot survive. It is important to consider keystone species when making any decisions that could affect the natural environment. A small impact on keystone species could cause major disruption for the whole ecosystem.