STRUGGLE FOR EXISTENCE 63 



numbers by various enemies ; for instance, on a piece 

 of ground three feet long- and two wide, dug and 

 cleared, and where there could be no choking from 

 other plants, 1 marked all the seedlings of our native 

 weeds as they came up, and out of the 857 no less than 

 295 were destroyed, chiefly by slugs and insects. If 

 turf which has long been mown, and the case would be 

 the same with turf closely browsed by quadrupeds, be 

 let to grow, the more vigorous plants gradually kill the 

 less vigorous, though fully grown, plants : thus out of 

 twenty species growing on a little plot of turf (three 

 feet by four) nine species perished from the other species 

 being allowed to grow up freely. 



The amount of food for each species of course gives 

 the extreme limit to which each can increase ; but very 

 frequently it is not the obtaining food, but the serving 

 as prey to other animals, which determines the average 

 numbers of a species. Thus, there seems to be little 

 doubt that the stock of partridges, grouse, and hares on 

 any large estate depends chiefly on the destruction of 

 vermin. If not one head of game were shot during 

 the next twenty years in England, and, at the same 

 time, if no vermin were destroyed, there would, in all 

 probability, be less game than at present, although 

 hundreds of thousands of game animals are now 

 annually killed. On the other hand, in some cases^ 

 as with the elephant and rhinoceros, none are destroyed 

 by beasts of prey : even the tiger iD India most rarely 

 dares to attack a young elephant protected by its dam. 



Climate plays an important part in determining the 

 average numbers of a species, and periodical seasons 

 of extreme cold or drought, I believe to be the most 

 effective of all checks. I estimated that the winter of 

 1854r-55 destroyed four-fifths of the birds in my own 

 grounds ; and this is a tremendous destruction, when 

 we remember that ten per cent is an extraordinarily 

 severe mortality from epidemics with man. The action 

 of climate seems at first sight to be quite independent 

 of the struggle for existence ; but in so far as climate 

 chiefly acts in reducing food, it brings on the most 



