ECOLOGY 



CHAPTER 37 



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Ecology and 

 Zoogeography 



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No organism, plant or animal, ever exists 

 in a vacuum. Every living thing is continu- 

 ally influenced by, and continually influ- 

 ences its surroundings. The inherited char- 

 acteristics which enable a plant or animal 

 to exist in terms of its surroundings consti- 

 tute its heredity. The surroundings, with 

 which it must conform, are its environ- 

 ment. Ecology is the science of the inter- 

 relationships of organisms in and to their 

 environment. 



One way of understanding the science of 

 ecology is to start studying the nature of 

 environments and to discover the demands 

 they make upon organisms that inhabit 

 them. We may begin by dividing environ- 

 mental factors into those that are primarily 

 physical— for example, light, temperature, 

 chemicals, water, and substratum— and those 

 that are primarily biological— for example, 

 the presence of plants and animals. 



A second approach is to study the organ- 

 isms. The ecologist usually starts with a par- 

 ticular plant or animal population, or 

 species, and his efforts are directed toward 

 the discovery of the types of environmental 

 conditions that can be tolerated by this 

 particular group. He also concerns himself 

 with conditions that actively or passively 

 promote the welfare of the group in terms of 

 survival and increase in numbers, as well as 

 those that mitigate against its success. 



It is significant that modern ecology is 

 much less concerned with organisms as in- 

 dividuals than as groups. Ecologists have 

 come to realize that it is the interaction of 

 consistent environmental constants, changes, 

 and cycles with relatively stable groups of 

 organisms that is of importance to the 

 orderly progress of evolution and survival. 

 The experiences of any one individual are 

 so variable and may be so atypical of those 

 of the group to which it belongs that it 

 obscures our understanding of the real prob- 

 lems presented by its environment. Any 

 integrated group of organisms of one or of 

 several species that occupies a consistent 



