In some cases, native species are able repel invaders
By Summit Voice
FRISCO — The world of biodiversity is filled with woeful tales of invasive species displacing native flora and fauna, but in some cases, the natives are able to repel the invaders.
In the case of a North American shrimp that made its way to European lakes and rivers in the past few decades, something has prevented the would-be colonists from overrunning the natives, so a team of scientists set out to figure out why. The results have been published in the open access journal NeoBiota.
By mapping the occurrence of the invaders, the researchers found that they only existed where native shrimps were absent or rare. When native shrimps were common, the American shrimp simply could not establish itself and disappeared.
‘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’ said Prof. Jaimie Dick, of Queen’s University, Belfast. “So we staged fights between two of our native shrimps, Gammarus pulex and Gammarus duebeni, and they both proved very effective at killing and eating the invader Crangonyx pseudogracilis.
“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. 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,” Dick said.
Invasion ecologists use the term ‘biotic resistance’ to describe how native species might fight back and drive invaders extinct. But unravelling how this occurs is not an easy task. By comparing the numbers of invaders killed over a range of their densities, the research showed that the native shrimps can kill most invaders to the point their populations crash, and hence the invasion is halted.
“Understanding how native species resist exotic species could help us prevent further invasions that damage crops, biodiversity and cost £Billions each year,” Dick 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.”
The authors are conducting more work in Ireland, England, Canada and South Africa to understand how native and invasive species interact and thus how to combat a very real environmental and economic problem throughout the world.