n 



* ,> 



I 



CHAPTER XLII. 



EXTi]srcTio]sr of species 



CONDITIONS "^TIICH ENABLE EACH SPECIES OF PLANT TO MAINTAIN ITS 



GROUND AGAINST OTHERS EQUILIBRIU:M IN THE NUMBER OF SPECIES HOW 



PRESERVED AGENCY OF INSECTS IN PRESERVING THIS EQUILIBRIUM — DEVAS- 

 TATIONS CAUSED BY LOCUSTS — EFFECT OF OMNIVOROUS ANIMALS IN PRESERV- 

 ING THE EQUILIBRIUM OF SPECIES — RECIPROCAL INFLUENCE OF AQUATIC AND 

 TERRESTRIAL SPECIES — HOW CHANGES IN PHYSICAL GEOGRAPHY AFFECT THE 

 DISTRIBUTION OF SPECIES— ^EXTENSION OF THE RANGE OF ONE SPECIES 

 ALTERS THAT OF OTHERS — SUPPOSED EFFECTS OF THE FIRST ENTRANCE OF 

 THE POLAR BEAR INTO ICELAND — INCREASE OF REIN-DEER IMPORTED INTO 

 ICELAND — INFLUENCE OF MAN IN DERANGING THE NUMERICAL STRENGTH 

 OF SPECIES — INDIGENOUS QUADRUPEDS AND BIRDS EXTIRPATED IN GREAT 

 BRITAIN — EXTINCTION OF THE DODO — RAPID PROPAGATION OF DOMESTIC 

 QUADRUPEDS OVER THE AMERICAN CONTINENT — POWER OF EXTERMINATING 

 SPECIES NO PREROGATIVE OF MAN — CONCLUDING REMARKS ON EXTINCTION. 



Conditions which enable each species of plant to 



MAINTAIN ITS GROUND AGAINST OTHERS. — I propOSO ill this 



cliaj^ter to treat of tlie various canses to wliicli the continual 



extinction of species^ both in the animal and vegetable 



creation^ are due. 



Every naturalist is familiar with the fact^ that although in 



a particular country, such as Great Britain, there may be 

 more than 3,000 species of plants, 12,000 insects, and a 

 great variety in each of the other classes ; yet there will 

 not be more than 100, perhaps not half that number, in- 

 habiting any given locality. There may be no want of 

 space in the supposed limited area : it may be a large 

 mountain, or an extensive moor, or a great river-plain, 

 containing room enough for individuals of every species in 

 our island ; yet the spot will be occupied by a few to the 

 exclusion of many, and these few are enabled, throughout 

 long periods, to maintain their ground successfully against 

 every intruder, notwithstanding the facilities which species 



VOL. II. 



F P 



