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How does the Australian brown tree snake to Guam jungle silence?

How far can range changes in ecosystems caused by non-native and invasive species? The venue has become a thrilling study Guam, the southernmost island of the archipelago of the Virgin Mary. The negative role of the main hero emerges brown tree snake, tree snake native to Australia. What happens describes studies of ecologists from Iowa State University (ISU).

Theoretically, it might seem that the story of the invasion mrštného a skilful hunter birds, brown tree snake, could not in any way surprising. This usually 1-2 m growing snake on Guam probably came during World War II, along with the obligations of military equipment. And on the island, which had no natural predator, he obviously pleased. Biologists have noticed his presence to the region fifties, but it was for most of the local bird population late. Of the twelve species of birds present bojgy care of full capture, ten, and the numbers of the two remaining reduced significantly.

"During the sixties, the situation has reached the point where the jungle on Guam just went quiet," says Haldre Rogers, an ecologist from ISU . "A silent to this day. Birdsong here you will hear only very rarely. "If you attracted vacation spot where you in the morning disturbing the birds, consider the following additional information: Treatment of snakes, although extinct birds and significantly reduced the even numbers of rodents, but there are now very, very spiders abound. A local brown tree snake, which reaches the abundance of local extremes to 3,000 individuals per square mile, are truly very aggressive and hungry.

Rogers, who is not afraid of snakes or spiders, but the island has released due to a completely different group of organisms. She was interested in trees. The woods had in recent decades experienced a striking transformation, both in terms of age structure, or at the level of species composition and distribution of trees directly. And it was Rogers, which gave an unexpected negative effect relation ptákožravých snakes and affecting the growth of trees. She noted the fact that they were probably extinct birds, who cared for the regeneration of the local vegetation.

"Five of the ten extinct species were frugivorních, they were fruit eaters, who was delivering seeds and droppings 70% of all trees on the island," says Rogers. "Without these birds but lost trees possibility of efficient distribution of seeds and greatly complicate their reproduction." In 2009, it conducted its first experiment in which the networks placed under trees catching the fallen fruit and seeds and then examined their germination. Shows, for example, that the seeds that did not pass through the digestive tract of birds had a 2x-4x lower germination.

Trees producing fruit, although they can renew that grows over from seeds under the crown of the mother plant, but certainly it will limit the initial surface area of ​​occurrence. In his last experiment then he showed that the disappearance of birds in the fifties and sixties of the last century to this day reflected in the decline in the number of seedlings of two previously most common species of fruit trees by 61 and 92%. A jungle on Guam today looks different than years ago. "It is yet less noticeable effect than the disappearance of birds," says Rogers. "Transformation of plant communities is because gradual and is increasing gradually."

But every cloud has a silver lining, even if they did not agree with the representatives of ten bojgou caught birds. Rogers praised the unusual opportunity to explore the ecology of mutualistic relationships between birds and plants. "Normally you would not implement an experiment in which you try to prove the importance frugivorních Spreading seeds for birds and forest regeneration. You would have had to remove from these birds really large areas. On Guam but something unique to itself offers. "He adds that Guam is in many aspects of direct and indirect effects of the invasion of alien species on ecosystems somewhat extreme case, but that similar situations should probably occur in other parts of the world.

Author: Radomír Dohnal

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