itself and spread, or the tendency of one or more species to 

 extend its range, cf. Population pressure. 



Biotic Province 



A major ecologic portion of a continent, occupying a 

 continuous geographic area, containing one or more regional 

 communities of plants and animals, e.g., Hudsonian biotic 

 province which occupies most of Canada and Alaska (Dice), 

 cf. Biome, Formation. 



Biotic Succession 



See Succession. 



Biotin 



A growth-promoting or stimulatory substance (vitamin 

 H), a member of the vitamin B complex. 



Biotope 



The smallest geographic unit of a habitat, characterized 

 by a high degree of uniformity in the environment and in its 

 plant and animal life, e.g., a decaying stump, a sandy beach, 

 cf. Biochore. 



Biotype 



A group of individuals occurring in nature, all with 

 essentially the same genetic constitution. A species usually 

 consists of many biotypes. cf. Ecotype. 



Bipolar Distribution 



Discontinuous distribution of a Taxon in the northern 

 and southern hemispheres. 



Birge's Rule 



A generalization which states that the Thermocline (q.v.) 

 is the transition stratum in lakes in which the temperature 

 decreases at the rate of at least 1C. per meter of depth. 



Bisect 



A line transect which shows the vertical and lateral dis- 



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