Animal Life in USA

Animal Life in USA

   The animal geography of the United States, however, is far from a natural pattern, for European settlement produced a series of environmental changes that grossly altered the distribution of animal communities.
   First, many species were hunted to extinction or near extinction, most conspicuously, perhaps, the American bison, which ranged by the millions nearly from coast to coast. But now rarely lives outside of zoos and wildlife preserves.
   Second, habitats were destroyed throughout most of the country — forests cut, grasslands ploughed and overgrazed, and migration paths interrupted by fences, railroads, and highways.
   Third, certain introduced species found hospitable niches and, like the English sparrow, spread over huge areas, often preempting the habitats of native animals.
   Fourth, though their effects are not fully understood, chemicals such as DDT were used for so long and in such volume that they are believed at least partly responsible for catastrophic mortality rates among large mammals and birds.
   Fifth, there has been a gradual northward migration of certain tropical and subtropical insects, birds, and mammals, perhaps encouraged by gradual climatic warming.
   In consequence, many native animals have been reduced to tiny fractions of their former ranges or exterminated completely, while other animals, both native and introduced, have found the new environment well suited to their needs, with explosive effects on their populations. The coyote, opossum, armadillo, and several species of deer are among the animals that now occupy much larger ranges than they once did.