Introduction to ecosystems
Introduction to ecosystems

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Introduction to ecosystems

6.3.2 Invasive alien species 

The tortoises that gave the Galápagos islands their name are now threatened by alien introductions. Goats have been a particular problem, but slowly the populations have been brought under control. The habitat, the wariness of goats and remoteness of the islands make eradicating goats a very expensive proposition.

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Goats compete with tortoises

DR. DAVID ROBINSON
When Darwin visited the Galápagos, almost every island was crowded with wildlife. Most large islands had their own species of tortoise, which could be identified by the distinctive shape of its shell. Today, some of these species are extinct, and on some islands, the tortoises are limited to nature reserves. The problem is people. Settlers to the islands have brought in farm animals and other nonnative species, which have had a devastating effect on native habitats. The tortoises, which gave the Galápagos Islands their name, have found themselves sharing their food with wild goats, the descendants of animals brought into the Galápagos by Ecuadorian fisherman and British pirates. The tortoises don't have the same reach as the goats. They're happy with handouts in the tortoise sanctuary, but find it harder to compete in the wild. On the island of Isabela, for example, at one stage, the goat population reached a staggering 50,000, and the national park authorities had to begin an eradication programme.
MICHAEL BLIEMSRIEDER
Eradication programme, in this case, means just get out and shoot these goats either by foot or by helicopter, or who knows, but we have to kill them so the vegetation can have a chance to recover.
DR. DAVID ROBINSON
By 2002, Isabela was cleared of its goat problem, and scientists were cautiously optimistic that the tortoises might be able to reclaim their territory.
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Like the animals on the Galápagos, much of the flora of the islands is also vulnerable to the impacts of introduced alien species. In recent years around 500 species have been introduced. Amongst the most devastating has been the red quinine tree.

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Eradicating the red quinine plant

DR. DAVID ROBINSON
The Galápagos are famous for their reptiles and birds. But much of the islands' flora is equally interesting, and it's just as vulnerable to the impact of humans. Over the last centuries, almost 500 species of plant have been imported into the Galápagos, some for agriculture, some for gardens, and some by accident. Like the wild goats who compete with indigenous tortoises for food, so these newcomers compete with local plants for sunlight, soil, and water. Santa Cruz, for example, is home to a unique species of plant called Miconia, which is only found on one other island. Today, it is under threat from the red quinine tree, first brought onto the islands in the late 1940s. The red quinine tree is very hardy, and it reproduces so rapidly that there were worries that it might wipe out the whole of the Miconia zone. Today, the National Park Service are actively engaged in a programme to eradicate the red quinine; injecting any seed-bearing trees with cartridges filled with herbicide. It's expensive, time-consuming work, and there are many trees to kill. But scientists are optimistic that they may eventually eradicate the most damaging newcomers.
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