What are Keystone Species?

A keystone species is an organism that has a remarkable effect on its natural ecosystem relative to its abundance. Such organisms are recognized as playing a crucial role in keeping an ecological community’s structure, affecting many other species in an ecosystem, and helping to define the kinds and numbers of various other species in the environment. Without keystone species, the environment would be dramatically different or cease to survive altogether.

In other words, every environment has certain species necessary for the survival of the other organisms in the system. The keystone species could be an apex predator or a natural plant.

Examples of Keystone Species

The wolf, Yellowstone’s apex predator

Keystone predators may enhance the biodiversity of regions by checking a single organism from becoming predominant. They can have an intense impact on the balance of organisms in a particular ecosystem. The removal or introduction of this predator, or variations in its population density, can have severe cascading effects on many other populations’ equilibrium in the environment. For instance, grazers of a grassland may check a single dominant species from taking over.

The exclusion of the gray wolf from the Greater Yellowstone Ecosystem had serious impacts on the trophic region. Without predation, herbivores began to over-graze many wooden browse species, changing the area’s plant populations. Also, wolves often kept mammals from grazing in riparian areas, which preserved beavers from infringing their food sources. The elimination of wolves directly influenced beaver communities, as their home became region for grazing. Extended browsing on conifers and willows along Blacktail Creek due to a lack of predation caused channel cut because the beavers assisted slow the water down, allowing the soil to stay in place. Furthermore, predation keeps hydrological characteristics such as streams and creeks in standard working order. When wolves were reintroduced, the beaver community and the whole riparian ecosystem improved dramatically within a few years.

Sea otters and kelp forests

Sea otters preserve kelp forests from destruction by sea urchins. When the sea otters of the North American west coast were shot commercially for their fur, their numbers fell to such sad levels – fewer than 1000 in the north Pacific ocean – that they could not control the sea urchin population. In turn, the urchins grazed the holdfasts of kelp so profoundly that the kelp forests largely vanished, along with all the species that survived on them. Bringing back the sea otters has allowed the kelp ecosystem to be healed. For instance, in Southeast Alaska, some 400 sea otters were rescued, and they have reproduced to form a population nearing 25,000.

Sea stars and other non-apex predators

Some sea stars may prey on mussels, sea urchins, and other shellfish with no other natural predators. If the sea star is separated from the ecosystem, the mussel population rages uncontrollably, driving out most other species. These creations need not be apex predators. Sea stars are prey for rays, sharks, and sea anemones. Sea otters are prey for orca.


The jaguar, whose numbers in South and Central America have been deemed as near threatened, acts as a keystone predator by its broadly varied diet, helping to balance the forest ecosystem with its consumption of 87 different prey species. The lion is another keystone species.

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