Keystone species

A keystone species is a plant or an animal that has a disproportionately large impact on a particular ecosystem. If a keystone species is removed from a particular ecosystem, the ecosystem will change dramatically. Removing a keystone species from an ecosystem often decreases that ecosystem's biodiversity. Keeping keystone species safe is important because they help maintain the health and function of ecosystems around the world.

Background

Robert T. Paine was an ecologist working in the Pacific Northwest in the 1960s. Paine observed the ochre sea star, Pisaster ochraceus, on a beach in Mukkaw (Makah) Bay, Washington. The sea stars are predators that eat mussels, barnacles, sea urchins, snails, and other small animals. Paine wanted to better understand the role the sea stars played on that particular beach. Using a crowbar, Paine pried all the sea stars from the rocks and tossed them into the ocean. He rid the entire beach of the sea star to observe the effects.

Paine found that removing this one species dramatically changed the ecosystem. Mussels nearly took over the beach when Paine removed the sea stars, which had been one of the mussels' main predators. Paine theorized that the sea stars were vital to the ecosystem. Without this species, the environment in the tide pool would change completely. The populations of mussels and some barnacles increased on the beach, but the total number of species living there was cut nearly in half.

Based on his observations, Paine developed the keystone species theory. In this theory, Paine explained that some species have a disproportionate effect on their surroundings. The species Paine focused on were predators—such as sharks, sea stars, and wolves—that helped control populations of other organisms in an ecosystem. Paine published his findings and explained that he believed Pisaster ochraceus kept the mussel and barnacle populations low, allowing other species to better compete for space and food in the ecosystem.

Dominant species are different from keystone species. Dominant species have important effects on their ecosystems and can help control the populations of other organisms. However, dominant species have powerful effects because of their large numbers. Keystone species are important because their effects on their habitats are disproportionate to their population sizes. Another factor that makes keystone species unique is that they are not redundant. If a keystone species is removed from an ecosystem, no other species will fill in to take its place.

Topic Today

Paine's hypothesis became famous, and it eventually became an important principle in ecology. Other scientists and researchers added to Paine's research and ideas over time. Researchers studied other species that could be considered keystone species, such as sea otters, wolves, elephants, and hummingbirds.

An example of a well-researched keystone species is the gray wolf. Humans began killing gray wolves in the American West in the 1800s and 1900s. By the 1950s, the animal was close to becoming extinct. People noticed that the biodiversity of Yellowstone National Park and other areas where gray wolves had been eradicated had suffered because of the wolves' disappearance. The elk population had become much higher because the wolves that had once preyed on them had been removed from the area. The high elk population ate more willow, aspen, and other plants. Other animals had problems competing with the large elk population for food and space.

Humans reintroduced wolf populations to Yellowstone. Once the wolves were reintroduced, they began killing more elk. As the elk population decreased, willow and other plants began to increase. Slowly, other species returned, and biodiversity in the area increased. Although the wolves had been a nuisance to humans, they were actually a keystone species that played an important role in the ecosystem.

Paine's research focused on predators as keystone species, but other scientists have identified other types of keystone species that have disproportionately important roles in their ecosystems. For example, North American beavers are keystone species in some areas. These animals cut down trees to make dams, and their dams change ecosystems. If beavers are removed from a particular ecosystem, other species will not take their place. Furthermore, one family of beavers can change an entire ecosystem by building one dam. Another keystone species that is not a predator is the hummingbird. Some types of hummingbirds in the deserts of North America, for example, pollinate native cacti and other plants. No other animals play that role in the ecosystem. Without pollinators, the cacti and other plants would not reproduce. The hummingbird plays the role of a keystone species in this ecosystem.

Although the idea of keystone species has become an important concept in ecology, some scientists have criticized it. Some researchers believe the term keystone species has become too broad and is now used to describe any species that has significant effects on an ecosystem, despite its population size. Furthermore, some scientists have questioned the validity of Paine's original experiment that led to the development of his theory. They have pointed out that Paine completed nearly all his research in one small area and did not complete the experiment in other locations. They believe Paine would have had different results if he had expanded the scope of his research and experiments.

Keystone species are vital to ecosystems around the world, and they help keep ecosystems healthy and functioning. Thousands of species die each year because of climate change and habitat destruction. Some scientists believe Earth is experiencing a mass extinction—one of only six mass extinctions in the history of the world. If this is true, a number of keystone species will likely go extinct. If keystone species go extinct, their absence will significantly alter the makeup of their former habitats. The biodiversity of those habitats will likely decrease, which will likely cause even more species to eventually die off. Scientists and researchers are trying to maintain as much biodiversity as possible to maintain healthy ecosystems. Protecting keystone species is an important part of maintaining biodiversity and functioning ecosystems.

Bibliography

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