CHAPTER XIV 

 SOME SOURCES OF OUR FAUNA AND FLORA 



HE .preceding chapters, if they have 

 accomplished their purpose, have given 

 the attentive reader the conception, 

 based on a good deal of detailed evi- 

 dence, that plants and animals are not 

 jumbled together in the outdoors in 

 chance assortments, but are grouped in 

 very definite associations, quite as clear 

 cut as are human societies. Indeed, sociology may be regarded 

 as the science of human ecology. This notion gives added zest 

 to one's excursions afield. You learn not only to recognize the 

 common-place forms but to study their groupings and to give 

 attention to those structural and functional adaptations by which 

 organisms are fitted to a specific environment. We have found 

 structurally very unlike forms, both plant and animal, closely 

 associated, and very like forms completely separated. The 

 rapids society of the stream is made up of fish, insect larvae of 

 many orders, crustaceans, leeches, and mollusks, a strangely 

 assorted family. On the dunes the closely related tiger beetles, 

 all predatory forms very similar in habit, were found each in its 

 particular zone. Ecological groupings of plants and animals 

 will often or usually cut across taxonomic groupings. 



Thus far, however, we have considered the matter from the 

 static point of view. We have considered the associations of 

 plants and animals as they are. There is a dynamic side. We 

 need to consider how they have come to be. The present 

 is the outcome of an eventful past and is to be explained as 

 the resultant of many forces operating through long periods 

 of time. 



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