1. Crawley, M. J. Phil. Trans. R. Soc. Lond. B 314, 711–731 (1986).
2. Rees, M., Kohn, D., Hails, R., Crawley, M. & Malcolm, S. in Biological Monitoring of Genetically Engineered Plants and Microbes (ed. MacKenzie, D. R. & Henry, S. C.) 9–24 (USDA and Clemson Univ., South Carolina, 1991).
3. Regal, P. J. Trends Ecol. Evol. 6, S47–S49 (1988).
4. National Academy of Sciences Introduction of Recombinant DNA-engineered Organisms into the Environment (National Academy, Washington, 1987).
5. Rees, M. & Long, M. J. Am. Nat. 139, 484–508 (1992).