Invasive plants don’t run amok

U. MINNESOTA (US) — Overachieving super-invader plants aren’t such a threat after all, according to a new study that finds when plants move to a new region, they are no more abundant than they were in their native range.

An international team of ecologists studied 26 species of grasses and forbs—flowering relatives of grasses that include clover, sunflowers, and milkweed—in North America, Europe, China, Australia, and New Zealand. Each species had moved from its native range to at least one new range, usually by jumping continents.

Most of those studied, including bluegrass and two species of clover, were equally abundant in their native and new ranges. Only 4-6 saw an increase.

The work should bolster efforts to contain the spread of destructive exotic plants by providing solid data about the likelihood of such events, says Elizabeth Borer, associate professor of ecology at the University of Minnesota.

The study is published in the journal Ecology Letters.

“USDA and other agencies want to decrease the risk to ecosystems from invasive species,” says Borer. “For example, yellow star thistle decreases the potential for cattle grazing.

“But in general, a species’ abundance in its native range predicts its abundance in a novel range. It doesn’t appear to be the case that new species necessarily take over, although some do.”

“It’s as if you only read medical journals. You’d conclude that all fungi and bacteria are bad for people, but that’s just what doctors study,” says co-author Eric Seabloom.

Too often, the ones that do take over the new territory just get all the press.

Species that show similar abundances in their native and new ranges should be regarded as the norm, the study says, and more concentration should be placed on the exceptions.

The study was carried out by ecologists around the world using the same experimental procedures so that data could be pooled with stronger conclusions.

“About five of us in the National Center for Ecological Analysis and Synthesis in California were looking at fundamental questions about what structures [ecological] communities,” Borer recalls.

“We had lots of data, but we wondered how comparable it all was. Then we thought ‘we can each develop an experiment, and we can each do it [using the exact same procedures].'”

The “Nutrient Network” ecologists realized that while invasive species don’t necessarily run rampant in a new range, invasions do change native plant communities in other ways.

“As sites around the world get more and more invaded, they become more similar to each other,” says Seabloom.

Elizabeth Borer and Eric Seabloom started the Nutrient Network to pool global data. (Credit: Tim Rummelhoff)

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