What a few rabbits can do

Azorella selago

Understanding the full impact of an invasive species on an environment is very difficult as it involves many factors, one of which is generally a long timescale. A team of researchers from France, Italy and Norway has found a natural historical record of the impact of an invasive species of rabbit on a remote Indian Ocean island. They used an environment with few interacting variables and a natural historical record - DNA found in a lake bottom.

A type of rabbit was introduced to the Kerguelen Islands, situated in a remote southern part of the Indian Ocean. In 1874 a group of scientists that were studying the transit of Venus brought the animals with them as a food source and when they disembarked they left behind several rabbits that quickly multiplied because there were no natural predators. Since then, the rabbits spread across much of the main island of Grande Terre, wreaking havoc on a delicate ecosystem.

To learn more about the impact the rabbits had on the island, the colleagues collected samples from the bottom of a lake which contained samples of plant DNA. They found samples dating back several hundred years, and were able to reconstruct the events after the scientists left the island. The region had been relatively stable for hundreds of years prior to the arrival of the rabbits. Then, in the early 1940s, when the rabbits made their way to the part of the island were the lake is located, things changed. Prior to their arrival, the dominant plant was Azorella selago; after their arrival, plant diversity plummeted and Azorella selago disappeared quickly. They also noted that erosion dramatically increased, although it did eventually level off, but the ecosystem was left unstable, and remains until today in spite of efforts to eradicate the rabbits. Instead, as the result of increased human presence in the area, other invasive species have made their way to the islands.