[APWG] Fwd: Friendly Invaders

[Bob Beyfuss]

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>To: rlb14 at cornell.edu, <jrh45 at cornell.edu>
>From: Gary Goff <grg3 at cornell.edu>
>Subject: Fwd: Friendly Invaders
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>>To: CCE-INVASIVESPECIES-L at cornell.edu
>>From: "Robert J. Kent" <rjk13 at cornell.edu>
>>Subject: Friendly Invaders
>>Cc: Charlie Scheer <cfscheer at optonline.net>
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>>
>>NY Times
>>September 9, 2008
>>
>>
>>
>>
>>Friendly Invaders
>>
>>
>>
>>
>>
>>By <http://query.nytimes.com/search/query?ppds=bylL&v1=CARL 
>>ZIMMER&fdq=19960101&td=sysdate&sort=newest&ac=CARL 
>>ZIMMER&inline=nyt-per>CARL ZIMMER
>>
>>New Zealand is home to 2,065 native plants found nowhere else on Earth. 
>>They range from magnificent towering kauri trees to tiny flowers that 
>>form tightly packed mounds called vegetable sheep.
>>
>>When Europeans began arriving in New Zealand, they brought with them 
>>alien plants ­ crops, garden plants and stowaway weeds. Today, 22,000 
>>non-native plants grow in New Zealand. Most of them can survive only with 
>>the loving care of gardeners and farmers. But 2,069 have become 
>>naturalized: they have spread out across the islands on their own. There 
>>are more naturalized invasive plant species in New Zealand than native species.
>>
>>It sounds like the makings of an ecological disaster: an epidemic of 
>>invasive species that wipes out the delicate native species in its path. 
>>But in a paper published in August in The 
>><http://topics.nytimes.com/top/reference/timestopics/organizations/p/proceedings_of_the_national_academy_of_sciences/index.html?inline=nyt-org>Proceedings 
>>of the National Academy of Sciences, Dov Sax, an ecologist at 
>><http://topics.nytimes.com/top/reference/timestopics/organizations/b/brown_university/index.html?inline=nyt-org>Brown 
>>University, and Steven D. Gaines, a marine biologist at the University of 
>>California, Santa Barbara, point out that the invasion has not led to a 
>>mass extinction of native plants. The number of documented extinctions of 
>>native New Zealand plant species is a grand total of three.
>>
>>Exotic species receive lots of attention and create lots of worry. Some 
>>scientists consider biological invasions among the top two or three 
>>forces driving species into extinction. But Dr. Sax, Dr. Gaines and 
>>several other researchers argue that attitudes about exotic species are 
>>too simplistic. While some invasions are indeed devastating, they often 
>>do not set off extinctions. They can even spur the evolution of new diversity.
>>
>>“I hate the ‘exotics are evil’ bit, because it’s so unscientific,” Dr. 
>>Sax said.
>>
>>Dr. Sax and his colleagues are at odds with many other experts on 
>>invasive species. Their critics argue that the speed with which species 
>>are being moved around the planet, combined with other kinds of stress on 
>>the environment, is having a major impact.
>>
>>There is little doubt that some invasive species have driven native 
>>species extinct. But Dr. Sax argues that they are far more likely to be 
>>predators than competitors.
>>
>>In their new paper, Dr. Sax and Dr. Gaines analyze all of the documented 
>>extinctions of vertebrates that have been linked to invasive species. 
>>Four-fifths of those extinctions were because of introduced predators 
>>like foxes, cats and rats. The Nile perch was introduced into Lake 
>>Victoria in 1954 for food. It then began wiping out native fish by eating them.
>>
>>“If you can eat something, you can eat it everywhere it lives,” Dr. Sax 
>>said.
>>
>>But Dr. Sax and Dr. Gaines argue that competition from exotic species 
>>shows little sign of causing extinctions. This finding is at odds with 
>>traditional concepts of ecology, Dr. Sax said. Ecosystems have often been 
>>seen as having a certain number of niches that species can occupy. Once 
>>an ecosystem’s niches are full, new species can take them over only if 
>>old species become extinct.
>>
>>But as real ecosystems take on exotic species, they do not show any sign 
>>of being saturated, Dr. Sax said. In their paper, Dr. Sax and Dr. Gaines 
>>analyze the rise of exotic species on six islands and island chains. 
>>Invasive plants have become naturalized at a steady pace over the last 
>>two centuries, with no sign of slowing down. In fact, the total diversity 
>>of these islands has doubled.
>>
>>Fish also show this pattern, said James Brown of the 
>><http://topics.nytimes.com/top/reference/timestopics/organizations/u/university_of_new_mexico/index.html?inline=nyt-org>University 
>>of New Mexico. He said that whenever he visits a river where exotic fish 
>>have been introduced, “I ask, ‘Have you seen any extinctions of the 
>>natives?’ ” “The first response you get is, ‘Not yet,’ as if the 
>>extinction of the natives is an inevitable consequence. There’s this 
>>article of faith that the net effect is negative.”
>>
>>Dr. Brown does not think that faith is warranted. In Hawaii, for example, 
>>40 new species of freshwater fish have become established, and the 5 
>>native species are still present. Dr. Brown and his colleagues 
>>acknowledge that invasive species can push native species out of much of 
>>their original habitat. But they argue that native species are not 
>>becoming extinct, because they compete better than the invasive species 
>>in certain refuges.
>>
>>These scientists also point out that exotics can actually spur the 
>>evolution of new diversity. A North American plant called saltmarsh 
>>cordgrass was introduced into England in the 19th century, where it 
>>interbred with the native small cordgrass. Their hybrid offspring could 
>>not reproduce with either original species, producing a new species 
>>called common cordgrass.
>>
>>Long before humans moved plants around, many plants hybridized into new 
>>species by this process. “Something like a third of the plant species you 
>>see around you formed that way,” Dr. Sax said.
>>
>>Biological invasions also set off bursts of natural selection. House 
>>sparrows, for example, have moved to North America from Europe and have 
>>spread across the whole continent. “Natural selection will start to 
>>change them,” Dr. Sax said. “If you give that process enough time, they 
>>will become new species.”
>>
>>“The natives themselves are also likely to adapt,” Dr. Sax added. Some of 
>>the fastest rates of evolution ever documented have taken place in native 
>>species adapting to exotics. Some populations of soapberry bugs in 
>>Florida, for example, have shifted from feeding on a native plant, the 
>>balloon vine, to the goldenrain tree, introduced from Asia by landscapers 
>>in the 1950s. In five decades, the smaller goldenrain seeds have driven 
>>the evolution of smaller mouthparts in the bugs, along with a host of 
>>other changes.
>>
>>In Australia, the introduction of cane toads in the 1930s has also 
>>spurred evolution in native animals. “Now that you have cane toads in 
>>Australia, there’s a strong advantage for snakes that can eat them,” said 
>>Mark Vellend, of the University of British Columbia. Cane toads are 
>>protected by powerful toxins in their skin that can kill predators that 
>>try to eat them. But in parts of the country where the toads now live, 
>>black snakes are resistant to the toxins in their skin. In the parts 
>>where the toad has yet to reach, the snakes are still vulnerable.
>>
>>Dr. Brown argues that huge negative effects of invasions are not 
>>documented in the fossil record, either. “You see over and over and over 
>>again that this is never the case,” he said. Species have invaded new 
>>habitats when passageways between oceans have opened up or when 
>>continents have collided.
>>
>>“The overall pattern almost always is that there’s some net increase in 
>>diversity,” Dr. Brown said. “That seems to be because these communities 
>>of species don’t completely fill all the niches. The exotics can fit in there.”
>>
>>In a recent paper in the journal Science, Peter Roopnarine of the 
>>California Academy of Sciences and Geerat Vermeij of the University of 
>>California, Davis, looked at the history of invasions among species of 
>>mollusks, a group that includes mussels, clams and whelks. About 3.5 
>>million years ago, the mollusks of the North Pacific staged a major 
>>invasion of the North Atlantic. Before then, the Arctic Ocean had created 
>>a barrier, because the mussels could not survive in the dark, 
>>nutrient-poor water under the ice.
>>
>>A period of 
>><http://topics.nytimes.com/top/news/science/topics/globalwarming/index.html?inline=nyt-classifier>global 
>>warming made the Arctic less forbidding. Yet the migration did not lead 
>>to a significant drop in the diversity of the Atlantic native mussels. 
>>Instead, the Atlantic’s diversity rose. Along with the extra exotic 
>>species, new species may have arisen through hybridization.
>>
>>The Arctic Ocean is now warming again, this time because of human 
>>activity. Computer projections indicate it will become ice-free at least 
>>part of the year by 2050. Dr. Roopnarine and Dr. Vermeij predicted that 
>>today’s mollusks would make the same transoceanic journey they did 3.5 
>>million years ago. They also expect the invasion to increase, rather than 
>>decrease, diversity.
>>
>>But critics, including Anthony Ricciardi of 
>><http://topics.nytimes.com/top/reference/timestopics/organizations/m/mcgill_university/index.html?inline=nyt-org>McGill 
>>University in Montreal, argue that today’s biological invasions are 
>>fundamentally different from those of the past.
>>
>>“What’s happening now is a major form of global change,” Dr. Ricciardi 
>>said. “Invasions and extinctions have always been around, but under human 
>>influence species are being transported faster than ever before and to 
>>remote areas they could never reach. You couldn’t get 35 European mammals 
>>in New Zealand by natural mechanisms. They couldn’t jump from one end of 
>>the world to another by themselves.”
>>
>>It is estimated that humans move 7,000 species a day. In the process, 
>>species are being thrown together in combinations that have never been 
>>seen before. “We’re seeing the assembly of new food webs,” said Phil 
>>Cassey of the University of Birmingham in England. Those new combinations 
>>may allow biological invasions to drive species extinct in unexpected ways.
>>
>><http://health.nytimes.com/health/guides/disease/botulism/overview.html?inline=nyt-classifier>Botulism, 
>>for example, is killing tens of thousands of birds around the Great 
>>Lakes. Studies indicate that two invasive species triggered the outbreak. 
>>The quagga mussel, introduced from Ukraine, filters the water for food, 
>>making it clearer. The sunlight that penetrates the lakes allows algae to 
>>bloom, and dead algae trigger an explosion of oxygen-consuming bacteria. 
>>As the oxygen level drops, the botulism-causing bacteria can multiply. 
>>The quagga mussels take up the bacteria, and they in turn are eaten by 
>>another invasive species: a fish known as the round goby. When birds eat 
>>round gobies, they become infected and die.
>>
>>“If you pour on more species, you don’t just increase the probability 
>>that one is going to arrive that’s going to have a high impact,” Dr. 
>>Ricciardi said. “You also get the possibility of some species that 
>>triggers a change in the rules of existence.”
>>
>>Dr. Ricciardi argues that biological invasions are different today for 
>>another reason: they are occurring as humans are putting other kinds of 
>>stress on ecosystems. “Invasions will interact with climate change and 
>>habitat loss,” he said. “. We’re going to see some unanticipated synergies.”
>>
>>Both sides agree, however, that decisions about invasive species should 
>>be based on more than just a tally of positive and negative effects on 
>>diversity. Invasive weeds can make it harder to raise crops and graze 
>>livestock, for example. The Asian long-horned beetle is infesting forests 
>>across the United States and is expected to harm millions of acres of 
>>hardwood trees. Zebra mussels have clogged water supply systems in the 
>>Midwestern United States. Exotic species can also harm humans’ health. 
>>“<http://health.nytimes.com/health/guides/disease/west-nile-virus/overview.html?inline=nyt-classifier> 
>>West Nile virus, 
>><http://health.nytimes.com/health/guides/disease/the-flu/overview.html?inline=nyt-classifier>influenza 
>>­ these things are invasions,” Dr. Ricciardi said.
>>
>>On the other hand, some invasive species are quite important. In the 
>>United States, many crops are pollinated by honeybees originally 
>>introduced from Europe.
>>
>>“It’s not that this is all good or all bad, and I’m not sure science 
>>should be the arbiter,” Dr. Brown said. “Placing values on these things 
>>is the job of society as a whole.”
>
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>
>Gary R. Goff
>104 Fernow Hall, Cornell University, Ithaca, NY 14853.
>ph. 607/255-2824;  fax 607/255-2815;  e-mail: grg3 at cornell.edu
>www.cornellmfo.info
>http://www.dnr.cornell.edu/people/ra/profiles/goff.html
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