Robert T. Paine carried out a research of species inhabiting a rocky shore in California. In his experiment he removed the top predator species – sea stars – from one section of his research plot. What he witnessed after, changed our understanding of the ecosystem functioning.
With the sea stars gone, almost half of other species gradually vanished, causing the collapse of the entire ecosystem. With this finding, the professor Paine discovered that some species have a larger effect on their environment than other species, regardless of their numbers. Such species are called “keystone species.”
Why are keystone species important for the environment?
The importance of keystone species lies in the way they affect other organisms in the ecosystem. According to Paine’s description, their presence is crucial for maintaining numbers and diversity of other species, which makes their role exceptional in the ecosystem .
The removal of a keystone species from an ecosystem triggers a set of negative changes. One such example is the overpopulation of one species, which leads to disappearance of other species. A well-documented case of such a chain of events was the elimination of wolves from the Yellowstone National Park at the beginning of the last century. The negative effect on the national park’s biodiversity was so profound that authorities have taken steps to introduce this keystone predator back.
While the decline of species in some remote ecosystems may not seem to be a reason to concern for us, the loss of biodiversity can have far-reaching implications. For example, a reduction of species diversity can be the first step to start extensive soil erosion, eventually leading to desertification that could extend far beyond their territory.
12 important examples of keystone species
Keystone species often dominate the attention of ecologists and policy-makers, who develop specific strategies for their protection, while media repeatedly report on their conservation status. Many of you have probably heard of them and perhaps wondered why these species get more attention compared to others.
As the examples below illustrate, in many cases the reason is that those species provide unique services to us and our environment.
African elephants – The oblivious creators
Elephants could be called engineers of African savanna. These great giants are a keystone species because of their ability to completely transform a landscape, bringing a variety of life alongside with them.
They shape their environment by pushing down trees, and eating small shrubs, such as acacia, creating and maintaining Africa’s iconic grasslands. 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. It also enables large predators like lions to have a bounty of prey to hunt .
It may seem that elephants leave behind a path of destruction by creating corridors through woodlands and digging deep holes in the dry river beds, but both of these actions are highly beneficial. Corridors prevent the spread of wildfires and deep holes collect water for other animals.
Elephants are important for people as well (not for ivory). In fact, they save lives! They are vital distributors of seeds from the Balanite tree. Many parts of this tree are used as famine food in some regions of Africa. Under normal conditions, just a fraction of seeds (less than 15 percent) turns into mature trees, but seeds digested by elephants are 50 percent more likely to start growing .
Grizzly bears – The diligent gourmets
The main reason why grizzlies are on the list of a keystone species is because they enrich the forest floor with nutrients from salmon carcasses. When bears feed on salmon, they often drag fish deep into the forest. Leftover carcasses from their grand feast fertilize forest soil with nitrogen and phosphorus, and support growth of strong and healthy trees.
On contrary to their reputation of a scary predator, the role of grizzlies in their ecosystem is more of a gardener. When digging for roots and bulbs to eat, bears turn over large areas of soil in mountainous terrain. This aerates soils and mixes in organic material, enhancing growth of many different wildflowers. Additionally, numerous seeds of berries and pine nuts get distributed through their feces .
Grizzlies also regulate the numbers of several prey species, like moose and elk. They maintain healthy populations of these species by hunting the weak individuals, or scavenging on carcasses and “cleaning” up the forest.
Sharks – The cleaning commando
For the past 400 million years, the ocean health has depended on sharks more than on any other marine predator. Sharks prey on the sick and weak members of other fish populations, and some also scavenge the sea floor to feed on dead carcasses. As such, their feeding habits help prevent the spread of diseases and regulate the size of fish populations .
Without sharks, the whole marine ecosystem would get out of balance, as some species would overpopulate and outcompete other, possibly even driving them to extinction.
Sea otters – The underwater forest rangers
This second smallest marine mammal that inhabits the waters of the Pacific Northwest is the key to stabilizing the coastal marine ecosystem. More specifically, sea otters feed on sea urchins, and in doing so, they control their population.
If urchin populations grew too large, they would eat the kelp that grows in the same habitat. Kelp – a giant seaweed – is a major source of food and shelter for numerous other species, such as crabs, snails, and geese. Many fish species also use kelp forests as their hiding spot from predators.
Kelp forests are not only valuable for marine species but also for us. They reduce coastal erosion by slowing down the impact of water on the shore, and play a role even in the mitigation of climate change, as their capacity to absorb carbon dioxide is astounding. According to scientists, healthy kelp forests sequester billions of kilograms of carbon from the atmosphere.
Krill – The nutrient couriers
Krill is a nice example that size does not always matter when it comes to being a keystone species. Even at the bottom of the food chain, krill has an irreplaceable role in the marine ecosystem as a carrier of nutrients.
These tiny crustaceans feed on phytoplankton, which is incredibly rich in life-promoting nutrients such as amino acids, antioxidants, carotenoids, bioflavinoids and omega-3,6 fatty acids .
Being the staple food of a whale diet, krill becomes their essential source of these rich nutrients. And not only for whales. Krill is eaten by seals, penguins, squid, fish, and has a long history of being harvested even for human consumption, especially in Norway .
Beavers – Two beavers are better than one
In many areas, beavers were hunted to extinction for their fur and to prevent the alteration of the landscape, because they can quickly divert or block streams. While in the past this behavior was considered harmful, we know now that by building natural dams on rivers and creating wetlands, beavers provide habitats for other wildlife and ideal spawning grounds for numerous species of fish like trout and salmon.
In fact, without beaver dams we would not have healthy salmon populations! Beaver dams trap fine sediment, letting only clean water pass through, which creates perfect conditions for salmon eggs downstream.
The service beavers do for the environment does not end with providing suitable habitat to other species. It is also the creation of wetlands that has an incredible value. Wetlands play a critical role in naturally removing pollutants from water and absorbing carbon more effectively than forests.
So, it seems that unlike our destructive interventions into the environment, beavers actually alter the landscape to bring more life and boost ecosystem services. Perhaps we are the ones to learn from them instead of prohibiting them from doing their work.
Hummingbirds and Honey Possums – The controversial couple
What does the tiniest bird of Americas and the Australian marsupial have in common? Both are a keystone species and both are the key pollinators to the unique vegetation in their area.
In the forests of Patagonia, a hummingbird species called Sephanoides sephanoides pollinates on its own nearly 20% of the local woody flora. In fact, many plants in the area can only be pollinated by hummingbirds. If these birds disappeared, the diversity of vegetation would decline and some species would possibly go extinct .
Similarly, honey possums are crucial pollinators of banksia trees, bridle bush and other shrubs of kwongan – the unique eco-region in Southwest of Australia. Kwongan is one of the global biodiversity hotspots with high numbers of endemic species that are endangered by habitat loss. While feeding on nectar, honey possums collect pollen on their snouts and carry it to other plants. The possum foraging activity secures healthy re-growth of vegetation, and therefore, protects this rare habitat for other animal species [9,10].
Parrotfish – The coral reef janitors
Parrotfish is one of the main caretakers of coral reefs. Every day this fish visits coral reefs and feeds on algae and coral branches, removing dead pieces and cleaning the coral surface. In fact, a single fish can consume up to 4,500 kg of material every year . By being such a good eater, parrotfish prevents algal proliferation in the reefs.
It is very important to keep algae species at check, because once algae dominate the reef, the healthy balance of coral reefs is irreversibly disrupted . Under extreme conditions, invasive algae might even kill corals, destroying the habitat of nearly 25 percent of all marine species .
Prairie dogs – The lifestyle influencers
Like the elephants in savanna, prairie dogs shape the face of prairie by affecting the plant composition and distribution of water in the landscape.
Being herbivores, prairie dogs feed on grasses and they do an amazing job in trimming them down. This allows other plant species to share the same habitat. Higher plant diversity attracts various insects, birds and wildlife.
Prairie dogs even alter the water cycle in dry conditions. When keeping the vegetation low, the plant surface from where water evaporates during hot days is reduced. Lower amount of water lost through evaporation equals more moisture in the soil and the area remains greener for longer periods of time.
The network of burrows that prairie dog colonies create also serves multiple purposes. It encourages water infiltration into underground aquifers, aerates soils, distributes nutrients and even provides shelter to other small wildlife .
African termites – The quiet skyscraper builders
These seemingly unimportant insects have some surprising characteristics. Did you know that some of the termite mounds reach as high as 30 meters and can be over 60 years old? Some animals even take advantage of the termite homes to raise their young because of the safety they offer. For example, mongoose and barbets build their nests inside.
Termite mounds are not only attracting free tenants, they also offer nutritionally rich ground for many plant species, even trees. According to scientific observations, Acacia trees are more likely to reproduce when in proximity to termite mounds. It is because the mounds contain high levels of nitrogen, phosphorus and important micronutrients such as iron or zinc .
So, it may not be directly the termites themselves who draw the diverse life in savanna together, but their mound building activity and nutrient accumulation certainly does.
Woodpeckers – The bird carpenters
Woodpeckers, also referred to as tree surgeons, live mostly a solitary life, but through their hard work they affect many other species. By excavating holes in trees, they create nests for numerous animals like bats, small owls, swallows, wood ducks and many more. All these creatures are dependent on woodpecker activity because they cannot make holes in hard tree trunks on their own. Abandon woodpecker nests provide much safer and sturdier shelter to them when compared to naturally created openings in trunks.
Besides “building” cozy accommodation units for other forest dwellers, woodpeckers also control insect populations. Their beaks can reach larvae in places other birds cannot access, and once they are finished scavenging, the excavated dents in wood leave remaining prey exposed to other species.
Woodpeckers are truly important for the health of the forest all year long, as they feed on some of the most destructive forest pests such as bark beetles and wood-boring beetles, and since they are not migratory, they keep populations of these pests at check even during the long winter months .
Saguaro cactus – More than just a western movie background
Who would have guessed that a cactus plant mostly connected with the popularized images of desert landscape actually sustains a lot of lives?
Saguaros, the tallest plants of the desert, offer perfect nesting opportunity for many birds. Bigger birds, such as red-tailed hawks, nest between branches, and smaller ones such as gila woodpeckers, purple martins, and elf owls create nests inside the fleshy stem.
At the same time, the juicy fruits of this plant ripen during the dry summer months and become the only moist food source for animals in that time of the year .
There are more…
The last example of a plant as a keystone species is just a tiny tap into the world of keystone food resources. If you want to learn more about keystone foods, have a look at this article, which describes why sugar maple trees and figs make the top of the list as irreplaceable food sources of their ecosystems.