Keystone species mussel population explodes uncontrollably, driving out most other species. These creatures need not be apex predators. Sea stars are prey for sharks, rays, and sea anemones. Sea otters are prey for orca. The jaguar, whose numbers in Central and South America have been classified as near threatened, acts as a keystone predator by its widely varied diet, helping to balance the mammalian jungle ecosystem with its consumption of 87 different species of prey. The lion is another keystone species. Keystone mutualists are organisms that participate in mutually beneficial interaction and the loss of which would have a profound impact upon
Predator (fictional species) and which drives them to hyper-aggression. When this gland is over-stimulated, it sends the creatures into a frenzied rage, causing them to attempt killing any living thing in sight, including members of their own species. This "kill rage" can be contagious and spread from one Predator to another, driving them all to attack each other. The Predators as a species barely survived the wars provoked by their kill glands, and they have learned to control the gland's secretions with artificial hormone regulators. In Ian Edginton and Alex Maleev's graphic novel "Aliens vs. Predator: Eternal" and the videogame "Predator: Concrete Jungle",