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Why Is The Bison A Keystone Species?

Bison is one of the most recognizable animals in North America. Bison are a keystone species, and I wanted to let you know why they need to be protected.

Bison contribute to the ecosystem by providing habitats for other animals, spreading plant seeds, and enabling other animals to feed in harsh climates. 

Bison were almost wiped out due to hunting. This would have caused widespread problems in the ecosystem. You can find out why bison are a keystone species and what their extinction would have meant for other animals and habitats.

Want to find out more information on why bison nearly went extinct. You can find out here in an article I have written.

Plains Bison

What Are Bison?

The American bison is North America’s largest land mammal. Their huge size and long coats characterize these gigantic animals. Bison may have poor eyesight, but their sense of smell and hearing is excellent. They are often called buffalos, but these can only be found in South Asia and Africa.

The North American bison consists of two species, wood bison and plains bison. These animals occur in the United States and Canada. They are quite a massive animal growing up to 11 feet long, with weights of 2000 pounds.

What Is A Keystone Species?

A keystone species is an animal species that has a tremendous impact on the environment relative to its abundance. If a keystone species is removed from its habitat, there will be an imbalance, hurting the ecosystem. 

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Why Is The Bison A Keystone Species?

The American bison is considered a keystone species for the habitat it lives in. Bison mainly live in the grasslands of the Great Plains. Bison create favorable habitats for a variety of animals and plant species in the Great Plains.


Bison has a distinct habit of wallowing, trampling, and moving from place to place as they forage food. As they move about to feed, the animals aerate the soil using their powerful hooves. This allows for the growth of a variety of plants and disperses native seeds.

Wood Bison

The bison has a thick fur and plant, and tree seeds often get caught in it. These seeds are distributed throughout the entire prairie that the bison roams.

The presence of bison increases plant productivity. The bison also improves nutrient cycles for the plants and increased the amount of nitrogen in the soil.

It does this through its frequent urination. Bison urine contains lots of nitrogen. The increase of nitrogen supports the healthy growth of a wide array of plant species within their habitat. 

Bison tend to graze continuously and defecate as they go. This boosts the quality of plant litter that is being returned to the soil. An area that has the bison within its boundaries has the healthiest of plant species. Seeds are also dispersed through waste from the bison.

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The bison has a habit of wallowing in the soil. The bison rolling in the soil makes it more compact. This helps the ground increase surface water retention, most notably during the rainy seasons.

After heavy rains, you can find temporary pools of water form in such places and, subsequently, various wetland species. Even after the ponds have dried out, some new plant species emerge, which are drought resistant.

Such plants are a source of food to herbivores during the tough times when vegetation is scarce.

When a bison dies, they are a source of food for scavengers and some predators. If the body decays, it provides a wealth of nutrients that go back into the soil.

This makes the land more suitable to support the growth of healthy vegetation. The patchy grazing habit of the bison also encourages plant diversity.


The plants that grow offer new habitats to many grassland birds. The bison maintains not only a healthy ecosystem but also a balanced one. Some birds, such as the magpie, ride on top of the bison to feed on insects found in their fur.

Prairie Dogs

Bison also contribute to other keystone species, such as prairie dogs.

Prairie dogs are primarily herbivores. They contribute to a healthy ecosystem by providing shelter to several other animals.

Prairie dogs are also the primary source of food for the black-footed ferret. Without prairie dogs, there would not be enough food to sustain them. Animals such as the black-footed ferret would significantly reduce in numbers and be on the brink of extinction. 

There is a connection between prairie dogs and bison. Prairie dogs feed mainly on the short grasses within their range.

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The most significant impact of the bison on the prairie dog ecosystem is through their grazing. The bison like to graze in large patches, which they revisit throughout the season.

This means that there would typically be areas that have been grazed and those that have been left. Black-tailed prairie dogs will generally use areas that have been heavily grazed to dig their burrows. 

There is also a natural soil disturbance that occurs when bison graze. The grazing makes the soil loose enough for the prairies dogs to dig their burrows.

Abandoned prairie dog burrows make for an ideal habitat for other species of animals such as burrowing owls. They prefer prairie burrows because they are perfect places to lay eggs and raise the young ones.


The bison has a robust set of horns and quite a strong head. They can search for food in the winter using their large heads. They use their heads to push snow out of their way. This uncovers an area of vegetation, which helps other species survive during the winter. 

The pronghorn depends on the bison for its survival during this time of the year. Pronghorns are much smaller than the bison and cannot dig through the snow like the bison can.

Without the bison roaming the prairies, these animals would not survive the north’s long, harsh winters. Due to the bison uncovering vegetation with their heads, pronghorns can survive the winter.

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How Did Bison Almost Become Extinct?

Before the 19th century, approximately 50 – 60 million bison were roaming freely in North America. They were found between the Appalachian Mountains towards the east to the Rocky Mountains in the west. The bison herds were so large that they became a symbol of North America’s endless resources.

However, in the 1800s, the worst began to happen. Hunters almost entirely wiped out the bison population. There were less than a few hundred bison left by the 1880s; the rest had been wiped out. 

When European settlers arrived in the west, the massive slaughter began. The settlers took over the bison’s habitat, making the animal vulnerable.

Why We Need Bison?

There is no doubt that bison have a huge impact on the environment around them. Their impact on plant diversity is significant to other wild animals living within the area.

Many herbivores depend entirely on vegetation for their survival. If there were limited vegetation for them to feed on, they would die of starvation. Pronghorns, burrowing owls, and many birds would not exist in these areas.

The animals that prey on herbivores would also decrease in numbers due to a lack of food sources. The balance in the ecosystem would greatly have been affected if the bison had been wiped out. Bison must be protected at all costs.

For a complete guide to bison, you can read an article I have written. You can find it here.