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II 



Ecology 



ECOLOGY deals with the action of the environment on plants and animals 

 and their reaction, in turn, to the environment. These patterns have 

 been built up through thousands of years of evolution and one should 

 realize that not only have plants and animals evolved but so also has the 

 environment. 



When one considers parasites such as the tapeworm or the hookworm, 

 it is impossible to believe that they were always parasites. Sometime, in 

 the long dim past they were probably free-living. Organisms however can 

 change in man's memory too. The Colorado potato beetle was not always 

 a potato pest but fed on many western plants which were of no economic 

 importance. Not very many years ago it switched its diet and, using the 

 potato fields as highways, spread far and wide over the United States. 

 When plants and animals move to or are moved to different environments 

 they show startling responses in some cases. The English sparrow was' not 

 particularly numerous in the British Isles in the iSoo's but when brought 

 here to this country and released it increased enormously. The same 

 phenomena took place when the daisy, the dandelion, chicory, milfoil, 

 and devil's paint brush were introduced here from Europe. The Mongoose 

 became a pest in Australia and the muskrat became obnoxious in England 

 when introduced there. 



In regard to the changes in the environment, it seems to be well known 

 that the sea covered large areas of what is now dry land. Wherever we 

 find marine fossil shells or other remains in rock on dry land we have the 

 right to assume that the immediate area was once ocean bottom. We also 

 know that the climate of many regions now cold was mild if not sub-trop- 

 ical. In the rocks of Greenland for example one can find fossil leaves of 

 trees now found only in warmer places. We know that the Great Lakes 

 region was once covered with a thick sheet of glacial ice and this certainly 

 made a great difference in the kinds and amounts of organisms there. 



One of the chief studies in the science of ecology is the construction 

 of food chains. For example, the combustion of gases in the sun sends 

 waves of heat and light earthward. In the sea one finds tiny one-celled 

 green algae. These minute organisms absorb part of the light rays in their 

 green coloring matter or chlorophyll and with the use of carbon dioxide 

 and water they fix this light energy into the form of a sugar. This sugar 



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