All animal and plant species are important for nature. However, so-called key species have a particularly large influence, they are particularly important for biological diversity.

An example: wolves. After humans almost wiped out the wolf in Europe and the USA in the last century, this changed the ecosystems of the forests. Large ungulates such as deer and elk suddenly had no predators, they reproduced much faster than before, ate too much vegetation and trampled on areas they had not previously entered.

The now significantly larger ungulate populations changed the landscapes and destroyed habitats that were important for other species such as songbirds. Increased grazing led to increased erosion, which changed the course of rivers, which in turn affected entire coastal ecosystems.

Many of these key species are now threatened with extinction, putting entire ecosystems in danger that they have previously regulated.

In the early 1960s, American ecologist Robert Paine conducted a seminal experiment. After he removed a certain species of shellfish from a stretch of coast, the shellfish proliferated so much that they competed with each other for habitat.

As a result, the biodiversity of the area was greatly reduced, so that in some cases only one species of mussel lived there. Sea anemones and other species, on the other hand, had disappeared. For Paine, this is a clear sign that starfish play an important role in biodiversity in coastal ecosystems.

He described the starfish as a key species for this ecosystem, like the keystone at the top of a brick archway that holds all the other stones together. Key species are often predators at the top of the food chain.

But this is not true for all key species, some are also very far down in the food cycle: krill, for example, a small, almost transparent Antarctic crustacean, regulates the food chain of the Southern Ocean and feeds many animal species from whales to penguins and birds.

Krill is one of the richest food sources on our planet, without the mini-crustacean entire marine ecosystems would collapse. Other key species are also known as engineers of ecosystems, such as the beaver. He builds dams and at the same time creates deep pools that serve as habitats for young fish, turtles and frogs.

Key species are often particularly threatened, including American jaguars and ivory tree coral, which provides food and habitat for thousands of mollusc and fish species.

The jaguar, which once roamed a vast territory from Mexico to Argentina, is the largest big cat in the Americas. It keeps herbivores like deer and large capybaras at bay. This also preserves vegetation and limits soil erosion. If the big cat is missing, this has far-reaching effects.

However, the jaguar is already extinct in Uruguay and El Salvador. In Argentina it is threatened with extinction, there are only around 200 specimens left.

Elephants are also a key species, they maintain the grasslands of the African savannas. The animals clear shrubs and uproot small acacia trees, thereby preserving the habitat for grazing animals such as antelopes, impalas and gazelles. And when the world’s largest land mammal plows the ground and digs waterholes, zebras and giraffes also benefit, giving them a chance to survive periods of drought.

The elephant population has declined drastically in recent years due to poaching.

Plants also have key functions: the rather unspectacular green peat moss, for example, is a key species. Due to its excellent ability to store water, it is of great importance for the existence of moors. The moss plants also slow down decomposition processes in peat areas, which means that they emit less carbon dioxide. Peat bogs are important for the global climate because they store large amounts of CO2. When they are destroyed, bogs emit greenhouse gases instead of sequestering them.

In Europe alone, 22.5% of the plant species in bogs are currently threatened. And science clearly shows: without the moss species, the ecosystems in the bog cannot function effectively.

The sea otter is a key species to coastal ecosystems, but was nearly wiped out in the 19th century. After fur hunting of the otter was internationally banned in 1911, populations grew again, especially on the North American west coast.

Sea urchins and crustaceans had overgrown the seaweed forests there without their predators, which were now able to regenerate and in turn provided habitat for a variety of marine species, including fish and invertebrates such as squid and shrimp. Protected sea otters now ensure a species-rich underwater world from California to Alaska.

Wolves had been driven out of what is now Yellowstone National Park for over 70 years before being reintroduced in 1995. The idea was to bring an ailing ecosystem back into balance.

The return of the predator to the park, which is largely located in the US state of Wyoming, quickly paid off.

The wolves limited the number of elk and deer, so the plant life could recover. The animal carcasses killed by wolves served as food for a variety of species such as ravens, eagles and bears. As coyotes retreated from reclaimed wolf territory, other smaller predators and rodents benefited, according to the US National Park Service.

Fewer ungulates trampling the soil also meant that soil erosion decreased rapidly and plant species along the rivers were able to regenerate. This, in turn, brought back the beavers, who tended to building more ecosystems.

“It’s like kicking a pebble down a mountainside – a single pebble triggers an avalanche of change,” says biologist Doug Smith, who leads the Yellowstone Wolf Project.

Redaktion: Tamsin Walker and Jennifer Collins

This text was written in English and adapted into German

Author: Stuart Brown

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The original of this article “Climate and biodiversity: Why some species are particularly important” comes from Deutsche Welle.