SPECIAL ASPECTS OF ENVIRONMENT RESULTING FROM VARIOUS KINDS OF NUCLEAR WARS PARTⅡ Appendix 1-2 Historical Examples of Ecological Disaster(11)

摘要

The giant African snail (A. fulica) and the European rabbit (Oryctoiagus cuniculus) are life forms that have been introduced by man to regions outside their native habitats, where, unchecked by natural controls obtaining in their original environment, they pro liferated and spread with disastrous effect to ecological balance in the invaded areas. In these two historic instances the catastrophe is measured chiefly as economic loss manifested in two ways:directly, in the destruction of crops on which humans depend for food or Income;indirectly, by the creation of eroded lands unsuitable for pasturage or tillage and costly to restore to fertility, and in the cost of attempts to control the pest. Introduction of predators of A.fu1ica has resulted in unexpected chain reactions among various species. Inoculation of Oryctoiagus cuniculus with a virus disease, myxomytosis, killed millions of rabbits, but the population is again building up from individuals who acquired immunity either because of natural resistance to the disease or because-the virus itself is now present as a less virulent mutant. Control of these pests has not yet been achieved though each case is at least a century old. Biological controls. If "permanently" effective ones could be found, are most desirable since they are least expensive and are self-perpetuating. More likely, a combination of biological, chemical, and mechanical control methods will be developed to deal with the problems.