What Is A Keystone Species?

A mother sea otter with her pups. Sea otters are keystone species of their ecosystem.

What Is A Keystone Species?

A keystone species is the species whose presence protects the ecosystem from overpopulation or extinction. The concept of the keystone species was discovered by Professor Robert Paine from the University of Washington while studying sea stars in their natural environment in Makah Bay, Washington. Keystone species are classified into three groups: engineers, predators, and mutualists.


These are species that alter the environment to suit their needs, therefore altering the relationship of other species within the environment. Engineering keystone species can be grouped into allogeneic engineers and autogenic engineers. Allogeneic engineers primarily consist of animal species, and alter the environment by molding existing materials into a new form. A prime example is termites which burrow the soil and use it to build termite mounds which are subsequently used by many other species as a habitat. Human beings can also fall in this category due to agricultural activity, which has caused other species like rodents and birds to change their interaction with the environment. Autogenic engineers on the other hand alter the environment by altering themselves. Examples are trees, whose structures are used by many other species for food or shelter. In tropical forests, there are species of primates who exclusively spend their entire lives on the canopy of the trees. Another example is coral, which is an invertebrate that grows and colonizes extensive areas of the ocean to create reefs which is an important residence for fish, mollusks and many other marine creatures.


Predatory keystone species are those which limit the growth of other species by preying on them. The absence of such species can have disastrous effects on the ecosystem as the lower species (prey) will overpopulate and deplete the existing resources. Examples of predatory keystone species include most of the big cats, sea otters and sharks. These animals are top of their respective food chains and usually have no natural predators. Although they consist of a minority of the biomass, their presence influences the interaction of the other animals within the environment. Spiders are examples of predatory keystone species as they prey on a wide array of insects which have a very high rate of reproduction. Their indiscriminate hunting method also helps in checking the population of insects which would otherwise cause a strain on the environment.


Mutualist keystone species are species who have a mutually beneficial relationship with their respective ecosystems, and would create disastrous effects if absent from the same ecosystem. This type of relationship is evident and crucial in the pollination and seed dispersal of plants. An example of a mutualist keystone species whose impact is felt by human beings are bees. Bees are a key component in the pollination of plants where some plants have no alternative to this effect. In the recent past, the global population of bees has seen a huge decline caused primarily by the use of pesticides in agriculture and this has seen a decrease in harvest in fruits.


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