The Native Species That Could

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When an “exotic” species is brought to a new environment and makes its home there, everything changes. Many native species die out as their biotic and abiotic resources are taken over or are fundamentally altered. Enormous damage is done as the invasive species spreads faster than people can eradicate it. Examples of destructive invasions can be found everywhere in the United States, from zebra mussels in the Great Lakes to kudzu in the South. However, new evidence is providing the hopeful message that not all native species necessarily succumb to invasions. As a striking example of evolution in action, scientists have found that some native species are adapting to the changes brought on by invaders, and can do so rapidly.

For example, toxic cane toads were brought to Australia in 1935. Today, less than 30 generations later, some species of snakes have evolved as a response. Australian black snakes from toad-invaded areas have acquired an increased resistance to the toad’s toxin. In addition, the black snake and other species, including the death adder, have evolved smaller head sizes in areas where the cane toad is present. The snakes with smaller heads cannot eat toads that are large enough to kill them, so natural selection has favored those with smaller heads.

Likewise, some plants in invaded areas have shown signs of adaptation. Cheatgrass is an invasive grass that has spread across the deserts of the Intermountain West. It sprouts earlier in the spring than the native grasses and saps nutrients from the soil. Cheatgrass is extremely flammable and has led to an increase in wildfires in the region. Once a fire has wiped out the existing vegetation, the invasive grass spreads farther across the open land.

Scientists compared several hundred native perennial grasses from communities with and without cheatgrass. Each plant was divided in two and brought to a greenhouse. One plant of each pair was grown with cheatgrass to measure its ability to survive and compete. They found that plants from the invaded areas had adapted by sprouting earlier, and two species began flowering earlier in order to better compete with the cheatgrass.

In another study, scientists found that a native grass called big squirreltail has adapted to cheatgrass invasion by developing smaller shoots and larger roots. The altered squirreltail roots take back the nutrients that cheatgrass has been stealing from the native plants and suppress the cheatgrass’ growth.

Other scientists have even found evidence of coevolution, in which both the native species and the invasive species have evolved in response to each other. Garlic mustard is a stubborn invasive herb that releases a compound called sinigrin. Sinigrin kills fungi that native plants need to absorb nutrients from the soil. However, a native species known as clearweed has shown increased resistance to garlic mustard. Garlic mustard has, in turn, adapted by releasing more sinigrin in areas where more native species are present. What may at first appear to just be a clump of boring-looking weeds, may actually be an example of a dramatic evolutionary arms race in progress.

1. Just because one population of a native species has evolved a response to an invader doesn’t mean another will, given the chance. How might strategic transplantation be used in the management of invasive species? Give a specific example.

2. Consider another invasive species that you already know about. Design an investigation to find out if any native species are adapting to the presence of the invasive species.

3. How could scientists determine whether genetic changes have occurred in adapted native species? What might be done with this information?

4. Speculate on the long-term consequences of native and invasive species evolution.

More to Explore
 Native Plants Evolve to Fight Off Invading Species
Coevolution and Evolutionary Arms Races
Native Species Fight Back: First Evidence of Coevolution Between Invasive, Native Species
Native Perennial Grasses Show Evolutionary Response to Bromus tectorum (Cheatgrass) Invasion

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