European Shrimp Destroy, Devour American Shrimp Invaders

An American shrimp has been launching an assault on Europe's rivers and lakes for decades now -- but to no avail. Unlike so many other invasive species, the shrimp seems to be largely kept at bay.

Curious to better understand the invader, researchers mapped the areas where the shrimp occurred, finding that it only existed where native shrimps were absent or few.

Based on this, the scientists hypothesized that wherever the two meet, the native shrimp is able to successfully root out the newcomers.

"We came up with the idea that the native shrimps might be eating the exotic species to the point of local extinction, and hence its patchy occurrence," co-author Jaimie Dick said in a statement.

To test this theory, the team staged fights between two native shrimps -- Gammarus pulex and Gammarus duebeni, both of which proved "very effective" at killing and devouring the American shrimps.

"Remarkably, one of the native shrimps. G. pulex, which almost never allows the invader to establish, was the better of the two predators in our experiments," Dick said. "The other native shrimp, G. duebeni, sometimes co-exists with the invader because it is a less effective predator. Thus, our laboratory experiments helped us understand a Europe-wide pattern of failed invasion."

Termed "biotic resistance," the phenomenon is not one that is always easily understood. However, by comparing the numbers of the American shrimp killed over a range of their densities, the study found that the European shrimp were able to kill most to the point of population crash, thwarting the invasion.

Knowing this, Dick says, has far reaching implications.

"Understanding how native species resist exotic species could help us prevent further invasions that damage crops, biodiversity and cost £Billions each year," he said. "If we act to help native species populations, we can reduce the menace of invaders. Finally we can begin to turn the tide on unwelcome and out-of-control colonists."