March 31, 1922] 



SCIENCE 



335 



vestigated in the Norman Bridge Laboratoi-y. 



Mr. Chairman, it is a great pleasure to me 

 to express the best and most hearty -wishes for 

 the good success of the work that has now been 

 set on foot. 



H. A. LORENTZ 



BIOTIC AREAS AND ECOLOGIC HAB- 

 ITATS AS UNITS FOR THE STATE- 

 MENT OF ANIMAL AND PLANT 

 DISTRIBUTION 



More precision in the statement of animal 

 and plant distribution has become an urgent 

 need. A specimen labeled "California" or 

 "Africa" is obviously of little value in a criti- 

 cal study of distribution. But, though less 

 obviously at fault, a record giving merely a 

 city or county as a locality is still not of the 

 greatest use. A number of distinctly different 

 kinds of life conditions occur within a short 

 distance of most towns, and in the western 

 parts of the United States the life conditions 

 within a single county may range from desert 

 to moist forest and even to perpetual snow. 

 Unless the life conditions under which a 

 species lives are known we can gain little in- 

 sight into the factors which govern its dis- 

 tribution. 



A knowledge of the life conditions under 

 which a species lives can not be obtained from 

 a statement alone of geographical localities, 

 no matter how exactly these may be given. 

 Even a record of the precise acre on which a 

 specimen has been taken means little unless 

 the environmental conditions of the spot also 

 are stated. Exact geographical records are 

 necessary, but mention alone of a locality is 

 not enough, and a complete record must in- 

 clude a statement of the environmental condi- 

 tions as well as the locality. 



Some sort of classification of the environ- 

 mental conditions must, of course, be adopted 

 if the conditions under which a species lives 

 are to be stated concisely and with precision. 

 Although I do not intend to propose here any 

 new system of classification, either for en- 

 vironments or for biological distribution, I do 

 wish to call attention to some of the units on 

 which a classification must be based. 



The units of biogeographical classification 

 which I believe will prove most generally use- 

 ful are two in number: (1) a unit of geo- 

 graphical extent forming a natural life area 

 (faunal or floral area), and (2) the habitat 

 or eeologie community. The statement of the 

 faunal or floral areas and the habitats or com- 

 munities in which a species is found, together 

 with records of geographical localities, should 

 give very accurately both the geographical 

 distribution and the conditions under which the 

 species exists. 



Biogeographers have long made use of 

 floral and faunal areas for the classification 

 of distribution, and the importance of this unit 

 of distribution is generally conceded. Some 

 ecologists employ practically the same con- 

 cept under such designations as "climatic 

 formation" and "climax formation." The best 

 term available to include the concept of both 

 floral and faunal areas seems to be biotie area. 

 A biotie area, then, may be deflned as a geo- 

 graphic district, characterized by an assem- 

 blage of species and of ecological character- 

 istics differing from those found in adjacent 

 areas. A biotie area will usually, though not 

 always, be also a climatic area, and will often 

 be a distinct physiogi'aphic area as well. 



The animal species found in a biotie area 

 constitute a fauna; the plant species found in 

 the same area constitute a flora; and the com- 

 bined animal and plant species of the area 

 may be termed a biota. 



It has been generally presumed that the units 

 of classification for ecological distribution and 

 the units of biogeographical classification be- 

 long to different categories and can not be 

 used together. However, I see no reason why 

 the unit of ecological classification, the eeo- 

 logie community, may not, for the exact state- 

 ment of distribution, be combined with the 

 unit of geographical distribution, the biota as 

 above defined. In fact, I firmly believe, after 

 considerable experience in the use of this com- 

 bination in the field, that it forms an excellent 

 method of stating distribution. 



By this method each biotie area is considered 

 to he made up of a number of eeologie habitats, 

 the animals and plants of each habitat form- 

 ing an eeologie community. The community 



