No. 571] 



TERRESTRIAL ASSOCIA TWX: 



131 



type, of the animal assemblage. These relations, how- 

 ever, are quite general, lacking detail. Detailed consid- 

 erations may be geographic, including geographic range 

 of species and of communities, and the distribution of 

 species and of individuals into communities; and they 

 may also be local, dealing with interrelations of plants 

 and animals within the area of the community. 



A. Geographic Kelations of Terrestrial Plants 

 axd Animals 



1. Geographic Range: The Province.— If one were to 

 plot the geographic range of the plant species found to- 

 gether in a given climatic habitat, a general correspond- 

 ence in distribution would be made apparent, a large 

 number of the species ranging more or less continuously 

 over a common, rather definite area (cf. Transeau, 1905). 

 The similar ecological constitution of these plants and 

 their consequent selective distribution into similar envi- 

 ronmental complexes gives a uniformity to the vegeta- 

 tion over the geographic region in which these environ- 

 mental conditions are found, and the resulting vegeta- 

 tion unit is known as a vegetation province (Gleason, 

 1910 : 42). The area of the province is generally uniform 

 in physical conditions. This uniformity is only relative, 

 being subject to gradual geographic variation in climate, 

 perhaps giving rise to subregions in distant parts of the 

 province, and to abrupt local variations in soil, water- 

 content, exposure, etc., giving rise to local or edaphic 

 plant assemblages very different from those of the cli- 

 matic or geographic type. Thus the prairie province 

 occupies the winter-dry interior region of North America. 

 Environmental variations from oast to west, climatic and 

 plivHOM-raphie, divide the province into the three sub- 

 regions of Pound and Clements (1898). Certain plant 

 species ran^e over one or all of these subregions, still 

 others establishing themselves over the whole area of the 

 province and also^smtteringly eastward, in dry treeless 

 parts of the deciduous forest province, to the Atlantic 

 coast. These last are also typical prairie plants, though 



