1. Aebischer, N.J., Coulson, J.C. and Colebrook, J.M. (1990) Parallel long-term trends across four marine trophic levels. Nature, 347, 753–5.
2. Ambuel, B. and Temple, S.A. (1983) Area-dependent changes in the bird communities and vegetation of southern Wisconsin forests. Ecology, 64, 1057–68.
3. Anon (1988a) Soil erosion tops crisis list. New Scientist, 117 (1600), 29.
4. Anon (1988b) Ban on lead shot gives swans new lease of life. New Scientist, 118 (1607), 18.
5. Arden-Clarke, C. and Hodges, D. (1987) Soil Erosion in Britain, Soil Association, Bristol.