Conclusions

The story of Hawaii's native flora reminds us what an impact invasive exotics can have on a broad range of species. The story of fish introductions in the Great Lakes shows us how difficult it can be to predict the effects of any of those introductions. The crayfish story cautions us that seemingly minor changes can have unexpectedly large changes. The zebra mussel is perhaps the most sobering story of all. Who would have guessed that a little clam could cause such trouble? What can we do?⁸

• Keep non-indigenous species out until they are known to be safe - an instance of the precautionary principle. Purposeful introductions for biological control efforts need to be carefully examined. Note the possibly conflicting values of reducing chemical use and protective native plants and animals.

• Develop early monitoring programs to detect invasions while they are small enough to be more easily reversed or contained. Take advantage of the problems posed by life in small populations. With endangered species our concern was to prevent extinction. With invasive exotics our concern is to cause it.
  • In managing endangered species I suggested using a population viability analysis to identify vulnerable life-history stages so that management attention could be directed towards alleviating the passage through difficult life-history transitions.

  • In this case a similar analytical approach could be taken. The difference is that we'd try to make those transitions even more difficult than they currently are.

• Develop lists of species known to cause problems elsewhere. They are the most likely to cause problems if introduced in a new habitat.
  • Kolar and Lodge [6] illustrate how it may be possible to do a little better, in at least some cases. First, we must recognize that there are several hurdles that must be crossed before a species can be introduced and cause damage to native ecosystems (Figure 5).

    Figure 5: Obstacles to the establishment of introduced, invasive species. From Kolar and Lodge [6]

    

  • Using data on successful introductions and establishment in the Great Lakes, they produced a classification and regression tree (Figure 6) that allowed them to identify life-history variables that affect the chances of success at each stage and used it to identify 22 species from the Ponto-Caspian basin of central Asia that might become established through unintentional introductions in the Great Lakes. Of those 22 species, only 5 were identified as likely to become a nuisance.

    Figure 6: Classification and regression tree for introduction and invasiveness of freshwater fish in the Great Lakes. From Kolar and Lodge [6]

    

• If a non-indigenous species is consciously introduced, keep a record of the logic used to reach the decision and the consequences of the introduction so that the decision-making process can be improved.

• Be careful about deciding to eradicate a non-indigenous species once it becomes established. As the case of tamarisk shows, non-indigenous species may so change the structure of a community or ecosystem that eradication could have deleterious and unexpected consequences.⁹

This returns us to a theme I mentioned in my first lecture. Conservation biology tests our knowledge of ecological and evolutionary systems in much the same way as a well-designed experiment. To the extent we can predict and manage the impact of changes in a community's species composition, we have understood the dynamics that control it. To the extent we cannot predict and manage those dynamics, we have more to learn. Basic research in genetics, evolutionary biology, ecology, and systematics cannot help but provide us with the knowledge we need to manage ecosystems wisely. And our efforts to manage ecosystems cannot help but provide intellectual challenges for many years to come.