Lovich, Jeff. 1996.

Lovich, Jeff. 1996.. Wildlife as Weeds. California Exotic Pest Plant Council 1996 Symposium Proceedings. versión completa en pdf, 52 kB.

Wildlife as Weeds

Jeff Lovich
U.S. Geological Survey
Department of Biology
University of California
Riverside, CA 92521-0427

Introduction

In 1958, Charles Elton stated "we are living in a period of the world's history when the mingling of thousands of kinds of organisms from different parts of the world is setting up terrific dislocations in nature..." Modem ecologists are now well aware of the problems caused by the invasion of exotic species into natural areas and the attendant effects on global patterns of biodiversity (Clout 1995; Randall 1996). Once established, some exotic species have the ability to displace or replace native plant and animal species, disrupt nutrient and fire cycles, and cause changes in the pattern of plant succession (Vitousek 1990; Randall 1996).

The magnitude of changes wrought by invasive plant species fostered the development of several organizations, including the Exotic Pest Plant Council (Florida), the California Exotic Pest Plant Council, the Pacific Northwest Exotic Pest Plant Council, and the Tennessee Exotic Pest Plant Council, all dedicated to highlighting the challenges that invasive plant species pose to natural ecosystems and championing the causes of prevention, control and eradication. While this is a worthwhile endeavor, it is important to remember that invasiveness knows no taxonomic limits. Many animals have invasive tendencies and their impacts are often as great as or greater than those of invasive plants.

Humans have transported plants and animals for millennia. The Polynesians brought pigs, dogs, rats and other animals when they arrived in Hawaii (Steadman 1995). The Spaniards brought horses, donkeys, cattle and sheep to the New World. While these are familiar examples, there are many others that are relatively unknown to most people. The purpose of this essay is to highlight a small portion of the portfolio of "weedy animals" and examine their impacts on native ecosystems, with emphasis on the United States. For the purpose of discussion, an exotic or "weedy" animal is defined as a species that is established in an area (where it was historically absent) because of human activities. …

Conclusion

History has shown repeatedly that introduction of exotic species into areas that they did not occupy in historical times can, and often does, have dramatic impacts on native ecosystems. Some species were introduced with the best of intentions: mosquito fish for control of malaria and other human diseases, and cane toads and mongooses for the control of economically devastating agricultural pests. Others, like zebra mussels, were introduced accidentally. The key is whether or not we will learn from these mistakes.

Ironically, exotic animals can have beneficial impacts by controlling other exotics. Grass carp (Ctenopharyngodon idella ) are highly effective at removing unwanted exotic vegetation such as Hydrilla from aquatic systems. However, the fish's effect on desired aquatic vegetation can be disastrous when unchecked. Production and controlled release of sterile triploid grass carp is an effective way to control vegetation without establishing breeding populations of the carp (Clugston and Shireman 1987; Bain 1993). Similarly, the common carp ( Cypinus carpio ), a native of the Old World, has recently been shown to eat highly invasive zebra mussels ( Dreissena polymorpha ) in the Mississippi River (Tucker 1995). However, native species such as the turtle Graptemys geographica, also eat the mussel (Serrouya et al. 1995).

In the final analysis, many introduced animals have caused enormous harm both ecologically and economically. Given this track record, and the difficulty of predicting the impacts of exotic species, it is absolutely necessary to prevent further accidental releases and the introduction of unwanted species. Animals that are perceived to have potentially beneficial effects should be released only after rigorous testing under quarantine.