Nipping Invasives in the Bud
Lisa Lofland Gould, Executive Director
Rhode Island Natural History Survey
Lisa L. Gould earned a BA in biology from the University of North Carolina, Greensboro, and an MS in zoology from URI. She is a co-founder of the Rhode Island Wild Plant Society and the Rhode Island Natural History Survey, a clearinghouse for ecological information in Rhode Island.
The fact that an organism sometimes becomes invasive is an often unexpected consequence of its introduction, deliberate or accidental. The majority of introduced organisms do not naturalize, much less become invasive. But when biological invasions do occur, there may be surprising repercussions. Who would have thought that the northern mockingbird would be able to expand its range north due in part to the abundance of multiflora rose fruit? Who could imagine that kudzu, laudably intended to save a precious resource, soil, would one day inhabit seven million acres of land and cost the agricultural community and taxpayers hundreds of millions of dollars each year in lost crops? How could we have known that the white-tailed deer population would multiply as the northeastern landscape reverted to forest during the 20th century? Or that the deer would shun prickly Japanese barberry and eat native shrubs instead, providing one less control on the spread of barberry? Could anyone have predicted that water in car tires imported from Asia would be teeming with Asian tiger mosquitoes, bringing with them the potential to spread dengue fever in North America? Scientists have aptly named invasive species biological wildfire: out of control and highly destructive.
More than 40 percent of the plants and animals on the U.S. endangered and threatened species list are considered at risk primarily because of invasive nonnative species. Habitat destruction and fragmentation, global climate change, invasive species, and the loss of biodiversity are tied together, part of a bigger picture of man's capacity to change an ecosystem in an inordinately short amount of time. We know so little about how these systems function, what these systems comprise, and how species interact within them. How is it possible to understand and predict change if we lack baseline information? More basic research on the content of ecosystems and how they function is clearly needed.
Scientists have begun to identify common characteristics of invasive species. Invasives tend to have high population growth rates, produce large quantities of fruit or offspring, be able to disperse over distances, mature rapidly, utilize generalized pollinators, and lack the diseases, predators, or herbivores that controlled them in their native environment. Habitat disruption, in the form of soil disturbance, landscape fragmentation, changes in water regimes, and changes in nutrient content of soil or water, enhances the capabilities of most invasive species to spread. Some species become invasive within a decade of their introduction, others can take centuries. Researchers are developing models to predict the potential invasiveness of introduced species, but such models will be intellectual exercises only if they are not used to make decisions about the plant and animal species that are deliberately brought into new areas.
Invasive species such as Eurasian water milfoil (Myriophyllum spicatum), hydrilla (Hydrilla verticillata), mile-a-minute weed (Polygonum perfoliatum), water chestnut (Trapa natans), and zebra mussel (Dreissena polymorpha)---to name a few that are already in nearby states---may soon appear in Rhode Island. With climate change predicted, we shouldn't be surprised when species invasive in southern states---such as water hyacinth (Eichhornia crassipes), kudzu (Pueraria lobata), Africanized honeybee (a strain of Apis mellifera), and Asian tiger mosquito (Aedes albopictus)---also begin to appear here.
The flow of invasive species will never stop, but perhaps it can be slowed down. Impediments to the introduction of invasives include stricter regulations for the handling of ballast water, greater support for federal agencies such as the USDA's Animal and Plant Inspection Service (APHIS, a first line of defense), self-regulation by the nursery industry, education of homeowners and others (such as departments of transportation) about ornamental plants, and a concerted effort to use native species in landscapes. Early detection and eradication programs are crucial, as is the refinement of control techniques, especially those that minimize the quantity of pesticides used and the disturbance of habitats. Public education is critical. This serious issue affects health, water supplies, fisheries, agriculture, recreation, property values, ecosystem function, and how tax dollars are spent.