Why Alien Species Thrive

planux writes "The Sacramento Bee has an interesting article about why invasive animal species thrive, pushing out native species -- sometimes to the point of extinction. Kevin Lafferty, a U.S. Geological Survey marine ecologist at the Western Ecological Research Center in Santa Barbara says "Invasive species end up with about half the parasites, or diseases, they had at home." Animals with an average of 16 parasites on their home turf typically bring about three of the parasites with them to new locations. And only about four new parasites will typically adapt to attack the invading species. Net gain: 9 fewer parasites!"

Comments

Really simple concept

[Cokelee]

A species new to an area has no known predators in that area. Hence, they may thrive and continue to do so until they have wiped out the population of the prey in that area. By that time overpopulation fixes itself because of a shortage in food supply. (or, think long term the development of resistence - if the given species feeds on plants, eventually they will start to taste bad to the species.

Basically, this is a built-in function of nature. It's just like life. When things are new and great you're happy, but you will adapt to your enviroment and will be bitchin about something soon - I promise.

It's just like a plant that I've always heard called the "devil's weed." It is a plant that takes over and kills all plant life it touches in the US. It came from China (IIRC), and it exists well in its naturally habitat - there are checks that make sure it doesn't grow like cancer. However, in the US these checks are not in place and it wipes out and strangles every plant it comes in contact with.

Don't mess with nature, I suppose.

Exploitation, diversity and evolution.

[goombah99]

this reminded me of an older paper that tried to rationalize why optimal growing conditions does not seem to favor rapid evolution of a species. That is what scant evidence there is, it appears that evolutionary diversity and advancement occurs under not the optimal growing conditions but rather in the harshest. e.g. at the highest altitude, hottest temperaures or any place life struggles to survive.

While its obvious that harsh conditions by themselves impose evolutionary pressure this does NOT promote diversity--after all that pressure only is placed on genes that govern adaptation to the environment, and even there there is generally a narrowing of the gene pool not an expansion.

No instead the diversity arises because you have left your old balanced environment and predators, and thus have LOST the finely honed evolutionary pressure on those genes. thus you can evolve semi randomly with little selective pressure, leading to diversity. Another factor leading not to diversity but to rapid differentiation is that when these new traits that have nothing to do with survival get chromosomally linked to the features that enhance a species survival in the harsh environment, they get amplified.

some people call this the poker hand effect. You dont need a royal straight flush to win. all you have to do is beat your opponents. Or to put it another way if you are trying to live in a chemical wasteplant out flow, you dont have to generate a a very good enzyme for digesting plastics, anything that is better than your competitors is good enough for now. You can evolve it more later.

this explanation is perhaps the simplest and best answer to creationists who want to insist that life is too complex a process to spring into existance fully developed (.e.g. behe's mouse trap argument). The answer is that being adaptive can beat being the best.

anyhow its interesting that a species poised to exploit an opportunity will evolve faster than one that dominates its native environment.

Not so simple concept

[jearbear]

At the same time, said new individual may be emerging into an environment it is totally unprepared for. Think of a plant going into an environment with lots of herbivores. While all of the native plants may have evolved nasty chemicals and physical defenses which have co-evolved with the local herbivores, the non-native plant has bupkis, and gets hammered as soon as it establishes itself.

Of course, there are a huge number of other wrinkles to this - higher dispersive ability and more efficient resource usage due to a the new plant not devoting any energy to costly defenses, etc., but this hypothesis was by no means a sure thing - that it has borne out is really quite extraordinary, and may yield some interesting insite into top-down versus bottom-up control of species invasions.

Great argument for space�colonization

[Mick D.]

I am only half joking when I say that. With all the debate nowadays about the value of manned space flight, this is actually a very good argument for putting people out there. Space is harsh and there are many perils that we have to learn to deal with out there. But, those are the equivalent to the new parasites in any new environment.

For a little idea of how many paraites we would bring with us just look at the Earth similar ailments that astronauts get. They rarely get sick and never get into car accidents.

It just goes to show that getting into space and staying there might not be as daangerous for the log stay as just visiting is.

Good book that deals with complex systems etc.

[muonzoo]

There is a really good book that addressing this, along with lots of other geek interesting things. I read it a few years ago, but it is equally interesting today as it was then.

If you have a favorite book search engine, then you might only want the details:
ISBN number: 0679425632
Title: Why things bite back: Technology and the Revenge of Unintended Consequences
Author: Edward Tenner
Publisher: Random House Canada
Published: May 1996

If you want, you can see it at Amazon, Barnes and Noble and Indigo.
Go read it. It's interesting.

OK, this is a stupid question, but...

[Unknown Poltroon]

Whynot transplant the speices thats being wiped out back to the invaders home territory? Would the opposite apply? Cane toads are wiping out the austrailian frogs, would transplanting the austraialn frogs to the cane toads native habitat work the same way? I konw it would be bad enviornmentally, but it would be a fun experiment.

Re:Complex concept

[Alsee]

Only a fraction (8-45% by region) of Africans have the trait, so probably people with it simply survive somewhat more often.

The key to understanding the genetics of sickle cell is to realize that the benefit is in having one normal gene and one sickle gene. In that case you get most of the protection against malaria and little of the harm of sickle cell.

Anyone with 2 sickle cell genes tends to dies of sickle cell anemia and anyone with no sickle genes tends to die of malaria. Most survivors will have one of each gene. The problem is that a population entirely of people with one of each gene is not "stable". When they reproduce their children will be 25% double sickle cell anemic, 25% sickle-cell-free and malaria vulnerable, and 50% healthy and protected.

The greater the malaria threat the closer the population will get to 50% sickle cell genes. As the threat diminishes the percentage will shift towards zero.

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