In the NYT, Carl Zimmer answers a mystery that didn’t seem to be much of a mystery:

Turning to Darwin to Solve the Mystery of Invasive Species

OCT. 9, 2014

An invasive ice plant growing on and killing a native Coprosma shrub on the coast of New Zealand. Carl Zimmer Invasive species are both a fact of life and a scientific puzzle. Humans transport animals and plants thousands of miles from where they first evolved — sometimes accidentally, sometimes intentionally. Many of those species die off in their new homes. Some barely eke out an existence. But some become ecological nightmares. In the Northeast, emerald ash borers are destroying ash trees, while Japanese barberry is blanketing forest floors, outcompeting native plants. Scientists aren’t certain why species like these are proving superior so far from home. “If natives are adapted to their environment and exotics are from somewhere else, why are they able to invade?” asked Dov F. Sax, an ecologist at Brown University.

The most obvious examples involve Australia, where Old World varieties, such as rabbits and Eurasians, have taken over. Australia is fairly big, but most of the land mass is too dry and the soil too ancient and worn out to support much life.

In contrast, the Afro-Eurasian landmass is the big leagues of survival of the fittest, so it’s not surprising that its winners tended to displace eccentric Australian types that didn’t have all that much competition while evolving.

Greg Cochran worked out the math: not surprisingly, big populations enjoy more favorable mutations than small populations, so a favorable mutation like, say, lactose tolerance is more likely to occur in Eurasia than in Australia.

Similarly, Australian firms don’t try too hard to compete in major global industries such as automobiles. (Automobile design and manufacture for export is dominated by firms from large home countries, with Sweden being the smallest country able to carve out a niche.)

A big part of the answer may be found in the habitats in which invasive species evolve. Many alien species in the northeastern United States, including the emerald ash borer and Japanese barberry, invaded from East Asia. But the opposite is not true. Few species from the northeastern United States have become problems in East Asia. In a new study published in the journal Global Ecology and Biogeography, Dr. Sax and Jason D. Fridley, a biologist at Syracuse University, argue that this is not a coincidence. They offer evidence that some parts of the world have been evolutionary incubators, producing superior competitors primed to thrive in other environments. “I don’t believe that all species are created equally,” said Dr. Sax. Until recently, ecologists trying to solve the mystery of invasive species paid relatively little attention to their origins, focusing instead on factors that might be helping them in their new homes. … But as far back as the 19th century, some scientists saw a role for evolution. In “The Origin of Species,” Charles Darwin wrote that we shouldn’t be surprised by native species “being beaten and supplanted by the naturalised productions from another land.”

Darwin reasoned that these victories were inevitable. Different species might adapt to a particular ecological niche in different parts of the world. Put them in the same place, in the same niche, and one might well outcompete the other because it has evolved superior attributes.

Darwin wrote: “At some future period, not very distant as measured by centuries, the civilised races of man will almost certainly exterminate and replace throughout the world the savage races.” Fortunately, protection of human biodiversity has improved since Darwin’s time. But, to cite two places Darwin visited, there aren’t any full-blooded Tasmanians left, and the Selknam tribe of Tierra del Fuego didn’t survive either.

Before Dr. Fridley and Dr. Sax met in 2007, each had become convinced that Darwin might be right. When they discovered they shared the same belief, they joined forces to test Darwin’s idea. Their approach was two-pronged. First, they looked at the places where invasive plant species tend to originate, examining the number of plant families in various regions. Invasive plants, they found, were more likely to have evolved in habitats with a great diversity of competing species. Darwin was right: Some plants have evolved to be fighters. “We were both kind of gobsmacked,” said Dr. Fridley. In the second test, Dr. Fridley and Dr. Sax looked at the role that canals have played in helping some species become invasive. Sometimes, humans have dug canals that linked ecosystems with an equal diversity of species. But in other instances, canals have connected regions with low diversity to those with great variety of species. The scientists predicted that invasive fish and mollusks would tend to come from places with high diversity and would have used canals to establish themselves in habitats with low diversity. … The story of the Suez Canal was very different. On one side was the Red Sea and the Indian Ocean, a huge, stable ecosystem with a deep diversity of fish and mollusks. On the other side was the Mediterranean, a relatively young habitat without nearly as much species diversity.

A recent theory is that the Mediterranean is only about 5 million years old, with water then pouring in over the Straits of Gibraltar in an almighty flood. (The Black Sea might be much younger, with connections to the stories of Atlantis and/or Noah’s Flood.)

Dr. Fridley and Dr. Sax found the Mediterranean was overwhelmed with invasive species from the other side of the canal, while hardly any from the Mediterranean took up residence in the Red Sea. Dr. Fridley speculated that a similar imbalance could explain why the Northeast gets so many invasive species from East Asia. Today both regions have a similar climate. But the United States was buried by glaciers during the Ice Ages, while East Asia was spared. Its species continued to grow more diverse, to evolve and eventually to become superior competitors — ready to invade, once humans started acting as their chauffeurs.

So, they are adding a dimension of time beyond the geographic dimensions of habitable space. North America is big, but it was covered with glaciers down to Chicago until maybe 12,000 years ago. My vague impression is that the Szechuan region of southwest China is particularly rich in spectacular plant species and even a few animals that haven’t gotten eaten yet (e.g., pandas). Did it not get covered by glaciers?

The NYT’s picture to illustrate the article is of ice plant, which mostly comes from Africa. It was planted all over California’s coastline a few generations ago, and looked fantastic with its mix of green, yellow, and red. Hitting a golf ball out of the ice plant on the dunes of the Monterey Peninsula is like hitting out of a pile of wet canvas sneakers.

Above is the fourth hole at Spyglass Hill, now widely considered the most brilliant design of Robert Trent Jones Sr.’s career. I hit the smartest shot of my life here in 1986. With the flag at the back of the 64 yard long and 8 yard wide green, surrounded by ice plant, the ret of my foursome floated wedges at the tucked away pin, just missing but winding up in the ice plant, to emerge six or ten strokes later. So, I choked up on a five iron and aimed a an oblique mound 75 yards to the right of the pin. I hit a low liner that deflected at a 45 angle off the mound and rolled and rolled and nearly hit the pin and went in for an eagle. Instead, though, it rolled to the back fringe from which I three putted. As Billy Pilgrim would say: And so it goes.

But ice plant is now being yanked out as “invasive” by the richest landowners, such as the Spyglass Hill golf course on the Monterey Peninsula.

The ice plant has now been replaced by indigenous species.