l8 ECONOMIC MAMMALOGY 



Some often-mentioned illustrations of the effect of disturbing the 

 balance of nature by introducing new elements into the fauna or by 

 increasing or decreasing the relative abundance of native species may 

 well be mentioned here. The mongoose (or mungoose), a great ratter 

 and mouser, was introduced into the West Indies to combat a rat 

 plague. When rats became less abundant and the mongoose numerous, 

 it attacked poultry, wild birds, young pigs and lambs and became a 

 great pest. 3 Disaster also followed its introduction into the Hawaiian 

 Islands and Porto Rico, where it has played havoc with native ground- 

 nesting birds. 4 



In a New York swamp snapping turtles caught young ducks, but 

 were kept in check by skunks, which ate the turtle eggs. When skunk 

 fur became fashionable trappers began to catch skunks. Turtles then 

 became more abundant, and because of their increased depredations the 

 ducks ceased to breed there, but returned to the swamp to nest after 

 boys thinned out the turtles by catching them for market. 5 



The fox, introduced into Australia, has become a menace to native 

 animals. 6 The far-reaching effects of the importation of gipsy moths 

 and English sparrows into the United States and rabbits into Australia 

 are too well known to need more than casual mention here. Because of 

 the destruction of their forage by rabbits, sheep in New South Wales 

 were reduced from 60,000,000 in 1893 to 32,000,000 in ig2^. 7 Cahn 

 tells of a lake containing abundant aquatic vegetation and various 

 species of game and pan fishes, into which carp were introduced, re- 

 sulting in the destruction of the vegetation, as well as of the native 

 fishes. 8 These instances are but a few out of hundreds that show the 

 danger of disturbing the natural adjustment of species. 



A classic and oft-repeated illustration of the effect the wholesale 

 destruction of one species may have upon others is Darwin's bumble- 

 bee story. The bees aid in fertilizing red clover by carrying pollen from 

 flower to flower. Field mice destroy the nests of the bees. Cats [and, 

 we may add, some other mammals and birds of prey] feed partly 



3 Morris, The mungoose on sugar plantations in the West Indies, London, 1883 ; 

 reviewed in Amer. Naturalist, xvn, 299, 1883. Palmer, Yearbook U. S. Dept. Agric. 

 for 1898, pp. 87-110. 



4 Wetmore, U. S. Dept. Agric. Bull., No. 326, pp. 38, 77, etc., 1916. 



5 Fisher, The economic value of predacious birds and mammals, Yearbook U. S. 

 Dept. Agric. for 1908, pp. 191-192. 



6 Le Souef, The fox menace and its effect on our native animals, Bull. Zool. Soc., 

 xxvn, 69-71, 1924. Journ. Mammalogy, v, 272, 1924. 



T Nature, cxn, 553, 1923. 



8 Cahn, The effect of carp on a small lake, Ecology, x, 271-274. 



