Valuing the chips on the exotic species table

The consequences and risks of exotic introductions are incalculable; strategies must include compromises

Negative consequences for natural communities of non-native species introduction can be considerable, and are neither well understood nor predictable. Perhaps the least-understood and potentially most harmful consequence is the loss of biodiversity resulting from the successful spread of exotic species. Santa Catalina's loss of 48 plant species as a result of the spread of non-native goats, for example, cannot be viewed as simply extirpation of plants; we've no way yet to accurately assess the long-term results of the corresponding loss of biodiversity.

Reasons for negative impact on natural communities and ecosystems are based in great part on the foreign characteristics of the non-native species. Melaleuca thickets in the Everglades have displaced native vegetation; kudzu and English ivy have overtaken native species; sparrows and starlings successfully compete with native species. Characteristics which were merely useful in its native habitat may function in a new habitat as advantages over native species, allowing eventual dominance. Indicators of weediness such as efficient dispersal, opportunistic feeding, and resistance to disease and local predation, combined with tolerance for factors limiting other species (such as the salt tolerance of cane toads), are likely to result in not only the spread of the new species but also the eventual eclipse of natives.

Such characteristics can be considered in determining whether an introduced species will harm existing communities. Negative effects, however, are difficult to predict; accurate assessments of the potential for harm could be gained only by accurately duplicating the target ecosystem and introducing the new species. Even then, results would not be indicative of potential harm; starlings we introduced repeatedly before resulting in a viable population.

Strategies for reducing the risks from introduction must consider the impossibility of determining with 100% accuracy the potential for harm. Workable strategies might, however, include components such as reduction of both intentional and unintentional introduction by increased public education and border control. Techniques for controlling the spread of exotics might include the development and application of technologies such as synthetic species-specific pheromones.

Because introduction is prompted by removal of barriers ~ geographical, physical/chemical, or biological ~ strategies for control might include the establishment of barriers. Constructing new oceans is not feasible, but introduction of a perimeter of sterile members of the species might be.

Alternative thinking about protection of biodiversity could produce creative and feasible solutions; for example, Madagascar's wild orchids are being collected and exported, often illegally, for international trade. A project raising orchid seedlings hopes to reduce this trade by providing a legitimate source of 'wild' plants. The project includes about 100 orchid species, raised from seed collected in the wild, in the Micropropagation Unit at Kew. The first seedlings are now being sent to Madagascar's Botanic Garden, where they will be grown on until large enough for sale abroad. The foreign currency earned should encourage politicians' interest in conservation issues.

Policies regarding early intervention and containment could do much to prevent negative consequences; tussock moth invasions in the Blue Mountains of eastern Oregon, for example, were a matter of grave concern to individuals who noted them 25 years ago. Confined at that time to perhaps 40 acres, and not burned out or sprayed as was suggested at the time, the moths eventually spread throughout eastern Oregon, devastating watersheds, forest health and biodiversity ~ an incalculable loss.

Any discussion of log imports must include examples of such consequences. It's argued that log imports could assist the disabled economy of the region, but at what risk? The timber-dependent Pacific Northwest would be better served by less risky and more potentially profitable economic development such as value-added manufacturing, log export bans, development of alternative (synthetic) resources, and economic diversification.

Economic factors, insufficient knowledge, and political reality are three reasons we've been unsuccessful in eliminating pests. Consider the transfer of exotic species via ballast water, for example. The release of 400 exotic species in three years in Coos Bay indicates the severity of the problem, but current economic realities would not allow for the shutdown of shipping at Coos Bay. Technical and political realities, at the same time, would prevent a ban on the use of water as ballast. Neither the knowledge of the occurrence and risk of species introduction nor the value (economic, social, biological, and abstract) of a preserved diverse ecosystem is yet sufficient to outweigh the political and economic benefits of continuing known introductions.

Economic and political reality won't ever allow for a total exclusion of exotic species, so we're left with compromises: How many exotic species, of which kind and number, in which places, are acceptable?

Which and how many political and economic compromises to prevent or deter exotic species are acceptable? What technological improvements are economically feasible, and who will bear the cost? What is the value of biodiversity, how large is the cost of its loss, and what are we willing to give up to conserve it?