INVADERS MAKE LIFE INTERESTING

by Whit Gibbons

May 15, 2011

Two disturbing types of invasions have occurred along the Mississippi River in recent times. Unstoppable, ever-rising floodwaters that are invading a region and know no master will always catch our attention. Residents over thousands of square miles of floodplain have been at the water's mercy. Once a flood is recognized as becoming a problem it is often too late to take effective action.

Let's hope that being too late does not apply to another type of invader to the region, one of an entirely different nature. I saw a disquieting photo awhile back of a man in Mississippi holding an ugly-faced, meat-eating piranha, a native of the Amazon Basin. The fish is known from tales about "man-eating" attack behavior on cattle, horses, and humans in the water. Although some of the stories are overstated, this fish and most others are not something we want to become established as invasive species in any rivers or lakes outside their native range.

An invasive species is one brought to a region, usually from another continent that successfully establishes itself. A piranha in a river in North America means somebody inappropriately released an aquarium pet into a waterway. As far as I know, piranhas have not become established in any U.S. aquatic system. But should they do so, a potential man-eating fish in our midst would quickly get our attention.

Pleas are made daily to federal and state governments to set controls on one invasive threat or another. But like a rising river, it may be too late to stop the flood. New introduced species enter our country and others every day. Transportation on a global scale is universal by land, air, and sea. Regulations have been set for importing some plants and animals, but considering the traffic overload, the controls and enforcement are minimal.

One fact about invasive species is that few generalizations can be made about what will determine the success or failure of any particular species. The findings of scientists can be contradictory. For example, three separate research studies of invasive plants in Great Britain identified certain seed characteristics that were in common to successful invaders. However, one study revealed that having large seeds made a plant more likely to be successful. Another study found that small seeds were the key to success. The third study concluded that seed size did not matter. So much for making predictions about which exotic plants will be most likely to populate England.

Another confusing example from scientific study of invasive species is that of the Brazilian pepper tree, a plant in the same family as poison ivy and poison sumac. The tree has become a major pest in southern Florida because it outcompetes native trees and supplants most varieties. According to one authority, Floridians had kept Brazilian pepper trees as ornamental plants for decades with no problems. Then suddenly in the 1980s they began to grow wild and create environmental havoc. No one had any idea in advance that they might become a problem. The ecological paradox is that scientists remain uncertain about whether any guiding ecological principles can be applied to predicting whether an introduced species will become a dominant and invasive part of the landscape or simply disappear.

Major laws and regulations have been proposed about how we should deal with the present-day pervasiveness of introduced species. The solutions make politicians uneasy and biologists do not always agree on what they are. But if we do not do something, many environments will be changed in ways that are unquestionably negative from most perspectives.

Anyone living alongside a flooding river is unhappy about the situation. Even before flood waters subside, people vow to become more vigilant about future flood control measures and about rebuilding. Being invaded by river floodwaters is a process with an ending; the water will eventually go away. The problem with many invasive species is that they never will. We need to be alert for the first signs that a new one is about to invade; we certainly don't want to find that flooded waters are transporting something like piranhas into new neighborhoods.

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