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Ch. XLII.] INCEEASE of one SrECIES DIMINISHES OTHERS. 447 



in mind, tliat wlien any region is stocked with as great a 

 variety of animals and plants as its productive powers will 

 enable it to support, tlie addition of any new species to the 

 permanent numerical increase of one previously established, 

 must always be attended either by the local extermination or 

 the numerical decrease of some other species. 



There may undoubtedly be considerable iluctations from 

 year to year, and the equilibrium may be again restored with- 

 out any permanent alteration ; for, in particular seasons, a 

 greater supply of heat, humidity, or other causes, may aug- 

 ment the total quantity of vegetable produce, in which case 

 all the animals subsisting on vegetable food, and others which 

 prey on them, may multiply Avithout any one species giving 

 way : but whilst the aggregate quantity of vegetable produce 

 remains unaltered, the progressive increase of one animal or 

 plant implies the decline of another. 



All agriculturists and gardeners are familiar with the fact 

 that when weeds intrude themselves into the space appro- 

 priated to cultivated species, the latter are starved in their 

 growth or stifled. If we abandon for a short time a field or 

 garden, a host of indigenous plants. 



The darnel, hemlock, and rank fumitory, 



m 



m 



If we enclose a park, and stock it with as many deer as the 

 herbage will support, we cannot add sheep without lessening 

 the number of the deer ; nor can other herbivorous species 

 be subsequently introduced, unless the individuals of each 

 species in the park become fewer in proportion. 



So, if there be an island where leopards are the only beasts 

 of prey, and the lion, tiger, and hyoena afterwards enter, the 

 leopards, if they stand their ground, will be reduced in num- 



If the locusts then arrive and swarm greatly, they may 

 ueprive a large number of plant-eating animals of their food, 

 and thereby cause a famine, not only among them, but among 

 the beasts of prey : certain species, perhaps, which had the 

 weakest footing in the island 



ber. 



may 



be annihilated, 

 animate creation 



