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Snail communities are similar throughout the world. Due shipping

An international research team looked at issues of global spread of species and concluded that human-mediated introduction of relatively immobile animals such as snails contributes to the homogenization of their biogeographical campus.

Scientists have focused on 175 kinds of non-native gastropods from 56 countries, who have now successfully colonize the territory thousand kilometers away from their original locations. It turned out that the countless snails biogeographical regions there are just two unified.

When the first human explorers out on the sea, they reached the farther, the more often the way they met a strange and unfamiliar species and alluded to previously unseen ecosystems. This phenomenon was mainly geographical barriers that have prevented the kind in which spreading beyond the far horizon. "Of course, one of the main barriers to the spread of species has always been the ocean," says Professor Henrique Pereira from the German Centre for Integrative Biodiversity Research (iDiv). " species from one continent will jointly shared evolutionary history, but species across continents had no connection. I therefore their evolutionary paths diverged. "

People over the last few centuries played the role of vectors, vector.
Often unintentionally because species transported from one continent to a completely new place. According to scientists, then this mediated transport contributed to the homogenization of biodiversity and perhaps change biogeographical regions. About how far this hypothesis is indeed true, we have decided to convince researchers from Portugal, Austria and Germany. Thus, they created a list of non-native species of gastropods and from them select the ones for which could be considered a human mediated proliferation. And then they look at the country of their original campus.

"Our point of view was distorted but initially,"
admits Pereira. "In the context of alien species of gastropods, we had looked at the statistics, the loss of species diversity and disruption over time. But then I thought to test a hypothesis about the similarities species within biogeographical regions. "The result? Before people began to contribute to the spread of the species found by the characteristic snail communities in every major biogeographical region. After human intervention, but this began to change communities and organized to form a unified two regions: the temperate zones and the tropics.

César Capinha, head of the study, adds: "And quite logically, all the communities of temperate regions have begun to be broadly similar, as well as the communities of the tropics." Before the era of human-mediated propagation, according to analyzes of scientists happened to two snail communities distant from each other 11,000 km shared a single common species. "At a distance of 6,500 kilometers was found a couple of exceptions, but even today the site apart over 20,000 km shares many of the same kinds of snails." rules of the game but changing.

While the geographic distance was still the main factor influencing similarity communities, it is now becoming an essential element of a similar climate. Now it and the existing connections (for example, transport of goods shipping) decide to what extent they will snail communities of two countries are similar. "Sort of species by biogeographic boundaries basically fell. Now, the limiting factor of the climate, "says Capinha." It's good to remember that the spread of alien species develops great pressure on native communities. Due to non-native species have become extinct in the last 500 years, more species than any other reason. "

Author: Radomír Dohnal

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