ENVIRONMENTAL RELATIONSHIPS 



Bandicoot 



Fig. 19.5. Adapti\'e radiation among; recent marsupial mammals of the Australian ree;ion. 

 (From E. H. Colbert, Evolution of the Vertebrates, copyris;ht 1955 by John Wilev and Sons, Inc., 

 reprinted b\' permission.) 



Having developed very efficient filters of "baleen," they are capable of in- 

 gesting the tiny herbivorous copepods in sufficient numbers to maintain life. 

 Various carnivores are able, by hunting in packs, to exhaust and pull down 

 large animals which would be beyond the abilities of the predators as in- 

 dividuals. Man, of course, by his inventiveness and ingenuity, obtains access 

 to any desirable food, from the tiny seeds of grain crops to the flesh of the 

 largest animals. 



Animal Populations, Competition, and the "Balance of Nature." 

 Theoretical considerations indicate that under ideal conditions the "innate 

 capacity for increase" of a species, its reproductive potential, is unlimited. 

 That is, populations are theoretically capable of increasing by geometrical 

 progression from generation to generation. The numbers of animals which 

 would be produced in even a few generations by such rates of increase are 

 almost beyond belief. Elephants are relatively slow breeders, but a single 

 pair of elephants would have at the end of 750 years nearly 19 million de- 

 scendants, if all the individuals lived 90 years and each female gave birth 

 to 6 young. More astronomical figures can be calculated for more rapidly 

 breeding forms. An insect, the cabbage aphid, can produce 12 generations 

 of ofl^spring between the end of March and the middle of August. Each 

 parthenogenetic female produces an average of 41 young. During a single 



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