an ecosystem. However, some species have a disproportionately large effect on their environment compared to their numbers. Such species are called “keystone species” and they have a critical role in maintaining the structure of a specific habitat, they can affect many other organisms in the same ecosystem and they can help determine the types and numbers of various other species in the community¹.
Very often keystone species dominate the attention of ecologists, policy-makers develop species specific strategies for their protection while media repeatedly report on their conservation status. So here are 12 examples of keystone species from across the world. Many readers will have already heard of them and perhaps wondered why these specific species get more attention compared to others. As the information below will illustrate, in many cases the reason is that those species have been determined to provide very unique services:
The theory of keystone species was based on Robert T. Paine’s research on the Pisaster ochraceus sea star found in a tidal plain on Tatoosh Island in the US. Paine determined that sea stars are a major predator for mussels and when the sea stars are gone, mussels then take over the area and crowd out other species².
Found in the Pacific Northwest, sea otters feed on sea urchins, and in so doing control their population. If the population of urchins was not controlled by sea otters, the urchins would eat up the kelp that is also found in the same habitat. Kelp, a giant seaweed, is a major source of food and shelter for the entire ecosystem with species such as crabs, snails, and geese depending on kelp for food while many types of fish using the kelp forests to hide from predators².
In African savannas, elephants eat small trees, such asacacia keeping the savanna a grassland and not a forest or woodland. This sustains grazing animals such as antelopes and zebras as well as smaller animals such as mice that burrow in the warm, dry soil of the savanna. Similarly predators such as lions and hyenas depend on the savanna for their prey².
In some forest regions in tropical America, figs serve as keystone food resources. Fig trees bear fruit throughout the year making figs the key food source for a large number of birds and mammals who rely heavily on this small group of plant species during the times of the year when other food resources are scarce³.
Many plant species can only be pollinated by hummingbirds and given the critical role of pollination for seed production and plant population survival, the presence of hummingbirds is critical for many habitats. For example, in forests of Patagonia, a hummingbird species called Sephanoides sephanoides is the only one that pollinates nearly 20% of the local woody flora⁴.
Because beavers create dams in rivers, they can significantly alter the nutrients, growth and abundance of local plants and animals. Beavers were introduced in an area of South America where no other native species could create dams in rivers. Once introduced beavers started altering the local ecosystems, replacing the slow-growing Nothofagus trees for meadows⁴.
A species of coral called Oculina arbuscula found in the US creates new habitat by forming complex branching colonies that provide shelter to over three hundred species that live and complete much of their life cycle around the coral’s branches⁴.
Bears can regulate the numbers of several species, like moose and elk, but what is perhaps not recognized as much is that they also spread seeds and fertilize their ecosystem. Bears that eat salmon will leave their dropping and partially eaten remains on the land providing nutrients such as sulfur, nitrogen and carbon to the soil⁵.
The gopher tortoise is the only native North American tortoise to occur east of the Mississippi river and can dig huge burrows, at a record of 47ft. Its burrows are shared by more than 350 other species, including owls, snakes, crickets and opossums⁶.
The grazing and burrowing activities of prairie dogs improve forage quality, conserve water, and improve the soil. More specifically, prairie dogs conserve water by eating leaves and therefore reducing the amount of water evaporated. The burrows they build then helps channel the water to underground aquifers⁷.
Sharks prey on the sick and weak members of other species populations, and some also scavenge the sea floor to feed on dead carcasses. As such, their feeding habits help prevent the spread of disease that could be devastating. It also strengthens the gene pool of the prey species⁸.
Sugar maple trees
These trees can transfer water through their roots from moist soil areas to dryer ones. This benefits nearby plants while the sugar maple tree provides shelter and habitat for many species⁹.