INTRODUCTION 25 



dependent on them and on each other, may be called 

 the "life- commonwealth," or biocoenosis} Thus there 

 are " bioccenoses " of the pond, the river, the wood, and 

 so on ; and also bioccenoses of a higher order, such as 

 the fauna — that is to say, the animal-life — of an entire 

 country. 



We need only consider any single animal in a 

 biocoenosis to see at once how it is really a member of 

 a community. Let us, for instance, examine the life 

 of the fox. For this purpose we must learn how that 

 crafty thief obtains his prey. But this implies further 

 that we cast a glance at the life of the animals he preys 

 on ; we must consider the speed of the mice in order 

 to appreciate the leap of the pursuing fox ; we must 

 know something about the hearing of the hare, to 

 understand how reynard can creep up to his victim 

 without being perceived. There is an old illustration^ 

 of the interesting mutual relations of fox and hare, 

 which shows very well how two species react on each 

 other in their condition. If we suppose that the hares 

 increase in any region that contains only these two 

 kinds of animals, the result will be that the foxes will 

 multiply in the same district, because the abundance 

 of food will make them stronger, and able to rear a 

 larger number of young. But the increase in the 

 number of foxes will require an increase in the quantity 

 of food; the hares will be less able to escape from 



^ This term was first used by Mobius, of Berlin, and was afterwards 

 extended and modified by Hensen and Dahl. Hensen insisted on the 

 statistical method as most important in the study of bioccenoses, so as 

 to discriminate between the normal and the accidental. 



* The instance is taken from Darwin. 



