FORMER INHABITANTS 



Beavers, foxes, bears, minks, antelopes, moose and^ elk_are very rare today.Wiid 

 turkeys, passenger pigeons, and heath hens are gone, with the buffaloes of the 

 plains. Such bison herds as the one pictured above are protected in national parks 



abundantly as they have done under man's care and cultivation. These plants, 

 as well as other species imported from various countries, have taken the place 

 of dozens of species that might otherwise have thrived on this area under 

 "natural" conditions. 



Transportation Man, moving with his household effects and his cattle 

 and his seeds for future planting, carries with him all the vermin, all the de- 

 structive parasites of his household and his associates. Europeans traveling to 

 the islands of the Indian and Pacific oceans brought with them infectious 

 diseases that turned out to be very destructive to the natives. The whites, in 

 turn, succumbed in large numbers to tropical diseases. Negroes brought as 

 slaves to America in the eighteenth and nineteenth centuries carried with 

 them an internal parasite, the hookworm, which they seemed able to tolerate 

 without serious discomfort or privation (see page 615), Later, however, when 

 this hookworm became established in the soil of our Southern states, the 

 parasites infested large sections of the white population, with disastrous effects. 

 Conversely, measles and other diseases long familiar to the white population 

 attacked the Negroes with exceptional severity. 



From these examples we see that a parasite moving into a new region may 

 find a host that is incapable of defending itself, and the parasite thrives. Or a 

 species enters a new region and becomes the prey of parasites against which it 

 has no defense. Or an invading species may be particularly destructive be- 

 cause it finds suitable food but does not run into its old enemies. 



588 



