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VERNBERG 



^.n\o qical niche 



Fig. 1 Interactions of an organism and its environment. (From F. J. 

 Vernberg and W, B. Vernberg, The Animal and the Environment, 

 page 2, Holt, Rinehart, and Winston, Inc., New York, 1970.) 



coupling of factors within the same subdivision. For example, 

 temperature and predation may be interactive in that a reduced 

 temperature may inhibit feeding in a species, which in turn would 

 reduce the amount of predation on the prey species. 



In addition to the external environment, the internal environ- 

 ment (internal milieu) of the organism is also a complex of many 

 factors. In some organisms well-developed homeostatic mechanisms 

 enable the internal environment to be relatively stable and indepen- 

 dent of fluctuations in the external environment. For example, some 

 aquatic organisms are excellent osmoregulators and maintain a 

 constant osmotic concentration of their body fluids even when the 

 ambient salinity varies. In contrast, the internal mUieu of other 

 organisms changes in direct response to changes in the external 

 milieu. Between these extremes of highly complex regulators and 

 perfect conformers is an array of aquatic species that provide varying 

 degrees of functional regulation. One species, for example, may show 

 different levels of regulation at different stages in its life cycle, at 

 different seasons of the year, or in different parts of its biogeograph- 

 icEil range. 



