Alien Species Can Disrupt Ecosystems

Invasive alien species: Ragweed (Ambrosia artemisiifolia) originated in North America, but global trade has long since brought the plant to Asia and Central Europe. It has become a serious problem for farmers and allergy-sufferers (Ragweed in the leaf development stage)

Increased prosperity and a growing population have led to a rise in international trade and are therefore the main factors responsible for the spread of alien plant and animal species, according to the results of a new study conducted by 26 international researchers that was recently published in the U.S. Proceedings of the National Academy of Science.

The migration of alien species can disrupt ecosystems, cause extensive damage to nature and agriculture and also trigger health problems. A prominent example of an invasive species jeopardizing public health is the spread of the giant hogweed (Heracleum mantegazzianum) in Europe and North America. Native to the Caucasus region, the plant was first brought to Western parks and gardens in the 19th century, and has since escaped and spread widely. The sap of the giant hogweed contains substances that can cause painful skin inflammations, especially when exposed to sunlight.

The scientists investigated which geographic, climatic and economic factors were decisive for the presence of alien species. The studies were conducted on the basis of data from the DAISIE database. In recent years, the EU project DAISIE (Delivering Alien Invasive Species Inventories for Europe) has registered all known alien species in Europe. Approximately 11,000 species were counted in Europe (www.europe-aliens.org).

The greatest numbers of alien species were found in areas with a high level of prosperity (pro rate assets of more than US$ 250,000) and a high population density (more than 91 inhabitants per km2). Countries in this category include Germany and Austria. The lowest numbers of alien species, by contrast, were found at a population density of less than 8.5 inhabitants per km2. Prosperity played no role in this case.