What Makes Invasive Species so Successful?

John David Russo (0707990)

October 14, 2010.

ENVS*1020*0140

Blog Assignment #2

A couple of decades ago, there did not seem to be any problems with taking a species from one part of the world and putting it in another if it was convenient. But what happens if the exotic species were to somehow get a foothold in the local ecosystems? At the time of moving these species this did not seem to be a concern but as time goes forward we are beginning to realize how these species can sometimes succeed too much in foreign environments and have a negative effect on the ecosystems natural balance. Exotic species that take hold in a foreign environment and known as invasive species. What make invasive species dangerous is that they may out-compete native species and cause the local extinction of one or more native species. One question on many minds is what makes invasive species so successful in foreign environments.

A study, titled “Challenging growth–survival trade-off: a key for Acer negundo invasion in European floodplains?” published in the Canadian Journal of Forest Research, tries to uncover what makes invasive species so successful. The study initially suggests that a species is likely to be invasive in a foreign environment if the traits that make the species naturally successful are not restricted by the new environment it is placed in. To try and determine what make exotic species invasive, the researchers choose to study the survival and growth rates of four different species of tree in three different areas in the Rhône floodplain in France.

One of the species chosen was an invasive species that has already taken a foothold in the area. This species was the Acer negundo L., which is considered to be a midsuccessional species. The other three species chosen are all native to the area and now survive alongside the Acer negundo. The one of the three native species is the Populus alba L., which is considered to be an early successional species. Another is the Salix alba L., which is considered to be an early successional species. The last is the Fraxinus angustifolia Vahl., which is considered to be a late successional species.

The forests in the area contain three different groups divided based on the tree species each contains, and their distance from the river. The first group is dominated by the two early successional native trees, Populus alba and Salix alba, this group is the closest to the river and is flooded yearly. The second group is dominated by the mid successional invasive tree species Acer negundo, it also includes old Populus alba, this group stands on an older part of the plain and is flooded often. The third group is dominated by the late successional native Fraxinus angustifolia, this group sits on higher land, known as upper terraces, and is rarely flooded.

For their experiment, groups of each tree type were placed in each of the different forest groups and their survival and growth rates were recorded. Within each of the different forest areas, groups the four tree species were planted so that each group would be faced with different situations and challenges. These included areas of little or high exposure to sunlight, or difference in soil conditions.

At the end of the experiment, the native species all had high survival rates in the areas to which they were accustomed and low survival rates in areas to which they were not. Populus alba and Salix alba survived well in high sun exposure but poorly in low sun exposure, where as Fraxinus angustifolia survived well is low sun exposure and poorly in high sun exposure. The invasive Acer negundo seemed to survive almost as well as Populus alba and Salix alba high sunlight exposure and almost as well as Fraxinus angustifolia in low sunlight exposure.

This could suggest that the exotic species is successful do to the fact that it takes a position between the two native species in its requirements to be successful. The invasive species fill an intermediate role that the native species could not and therefore thrives.

Works Cited

Saccone, Patrick, Jean-Jacques Brun, and Richard Michalet. "Challenging Growth–survival Trade-off: a

Key for Acer Negundo Invasion in European Floodplains?" Canadian Journal of Forest Research

40.10 (2010): 1879-886. Print.