PROBLEM 2 



Otir Relationship to Other Orga7?is?^?s 387 



natural enemies present, so they increase 

 more rapidly than before. 



Plant diseases are very common. Spe- 

 cialists all over the world are engaged in 

 studying them, looking for both cause 

 and cure. You can readily see that they 

 are of great importance when they de- 

 stroy plants that are valuable to us. 



Civilization changes our relationships. 

 As you have seen, our relationships to 

 other living things are complex and far 

 reaching. As civilization progresses we 

 enter into new and different relation- 

 ships with animals and plants. We domes- 

 ticate some animals and cultivate some 

 plants. As we travel from continent to 

 continent we carry animals and plants 

 with us. We cut down forests and plow 

 the prairies. Where your city or town 

 now stands there once was a forest or 

 plain. Not only has the vegetation been 

 destroyed but the birds and other ani- 

 mals that once lived there have moved 

 away or died. Rats and roaches, on the 

 other hand, have increased in numbers. 

 In every city there are likely to be more 

 rats than people. Wastes from our fac- 

 tories and sewage from our cities flow 

 into streams and kill the plants that are 

 the food of fish. A century ago the Hud- 

 son river and the Illinois river below 

 Chicago were well stocked with fish. We 



Fig. 337 A single tugboat cutting off the sun's 

 rays. Which organis7ns viight be affected by 

 this smoke? (sherman) 



gus kills the tree by killing the phloem 

 tissues in the bark of the trunk and roots. 

 This fungus was discovered in Holland 

 in 1919. No one knows how it got there. 

 In 1930 it was first reported in this coun- 

 try. It is believed that the fungus and 

 two species of bark beetle which carry 

 the fungus from tree to tree entered on 

 logs imported from France. They spread 

 rapidly. It is common for organisms that 

 are imported to spread with great rapid- 



ity. The reason for this is clear. In their 



original environment there are usually are constantly changing our relationships 



natural enemies which keep the organism with other organisms. Thus we create 



in check. When organisms are imported problems. You will read how we attempt 



into a new environment there may be no to solve these problems. 



Questions 



1. Give some examples of interdependence. Define ecology. 



2. Show how the relationships of animals and plants may change. 



3. How do our relationships differ.^ 



