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Global Ideas

Invasive species - not always a bad thing?

Biologist and journalist Cord Riechelmann says foreign species don’t always spell doom for their new ecosystems. He calls for active conservation of all species instead of aggressively weeding out the invasives.

When Christopher Columbus reached America in 1492, he ushered in what can be considered a new era in biology. Ships and boats sailing the world’s oceans have been transporting animals and plants from continent to continent on an unprecedented scale. In parts of the San Francisco Bay, where various ships have sailed for centuries, 99 percent of the flora and fauna are exotic. By exotic, I mean that these species are native to Africa, Europe or Asia, but not America. These species include birds like the Europeanstarling (Sturnus vulgaris) and the house sparrow (Passer domesticus).

A raccoon wanders through a residential area (Photo: Florian Möllers)

The common raccoon and the Chinese mitten crab are two of the most successful invasive species in Europe. But they haven’t proven to be much of a threat for local species.

The picture isn’t much different here in Europe, as the evolutionary biologist and ecologist Josef H. Reichholf describes in his book A Short Natural History of the Last Millennium: “Time and again, the conditions shifted through periods of warmer and colder climates, but in Central Europe, the climatic transition zone between the “Atlantic West” and the “Continental East” in particular remained a mixed area for flora and fauna with an apparently large capacity to take in (new species).”

Looking at the last 300 years alone, the loss of species would have been disastrous if new and foreign populations were separated from the native ones. That would mean that nearly all orchid species would disappear, as would the leafy chestnut trees that provide shade in our backyards and beer gardens.

A bad reputation

While the movement to stamp out orchids or chestnut trees never materialized, the Chinese mitten crab (Eriocheir sinensis) and the North American raccoon (Procyon lotor) weren’t so lucky. When they started to multiply in Germany in the 20th century, everyone started sounding the alarm. It was feared that the crab and raccoon, both omnivores, would literally rob native species of their food. But nothing of the sort happened. With both creatures, there was never any proof that they threatened the local flora and fauna. There weren’t even the slightest signs that they had increased the competition. Apparently, the American raccoon and the Chinese mitten crab had squirreled their way into areas that weren’t really being used. Still, it wasn’t a completely smooth transition.

A mitten crab that was caught in Germany (Photo: Jan Schilling)

Mitten crabs burrow through dykes and embankments, posing more of a threat to humans than to other animals.

Mitten crabs burrow into river banks and spend their entire adult lives in embankments and dykes. But that means they can disrupt and even destroy important river defense systems. Raccoons, on the other hand, can wreak havoc when they intrude in people’s homes. They are remarkably skilled at getting through doors and windows and into shelves, and they can leave a trail of destruction behind them. In both cases, it is human beings - not other animals - that suffer the consequences. On large landmasses like the U.S. or Europe, the majority of new species don’t seem to cause much of a problem. In America, there were no signs that the European starling and the house sparrow had a negative effect on the local bird populations.

Small island, big problem

A freight ship on the high seas (Foto: picture-alliance)

Navigating the open seas: invasive species become dangerous when they compete with native flora and fauna.

But when it comes to small islands, it’s a different story. Guam is a good example of the effect of invasive species on an island. Ever since the brown tree snake (Boiga irregularis) arrived in Guam, native bird species have all but disappeared. The snake has no natural enemies on the island and ideal living conditions, especially because the local bird populations didn’t know how to react to predatory snakes.

The effect on Guam has been particularly dramatic because there simply isn’t any cure. People there have to live with the snakes, which, for their part, don’t seem to have any problem with human civilization. For example, scientists even discovered crumpled pieces of plastic wrap that were used to package raw hamburgers in the serpents’ stomachs. So the brown tree snake can feed off the contents of our refrigerators.

The results are already comparable to the arrival of rats on Mauritius some four hundred years ago. Those rats managed to push the Dodo, a one-meter large flightless bird, into extinction because it didn’t have any way to defend its nests from the versatile predators - and it will be the same story for most of Guam’s bird species.

The only way to preserve the rest of the native birds is to protect certain species, in a very careful and targeted way. And that can only work if you educate and involve the local population on the island. So protecting species is not about fighting what’s already a losing battle against invasive foreign flora and fauna: it’s an effort to educate and preserve what’s already there.