

~$ Struggle for Existence. Chap. W. 



believes that "more than two-thirds of them are thus destroyed all 

 over England." Now the number of mice is largely dependent, as 

 every on°e knows, on the number of cats ; and Col. Newman says, 

 " Near villages and small towns I have found the nests of humble- 

 bees more numerous than elsewhere, which I attribute to the num- 

 ber of cats that destroy the mice." Hence it is quite credible that 

 the presence of a feline animal in large numbers in a district might 

 determine, through the intervention first of mice and then of bees, 

 the frequency of certain flowers in that district ! 



In the case of every species, many different checks, acting at 

 different periods of life, and during different seasons or years, pro- 

 bably come into play ; some one check or some few being generally 

 the most potent; but all will concur in determining the average 

 number or even the existence of the species. In some cases it can 

 be shown that widely-different checks act on the same species 

 in different districts. When we look at the plants and bushes 

 clothing an entangled bank, we are tempted to attribute their pro- 

 portional numbers and kinds to what we call chance. But how false 

 a view is this ! Every one has heard that when an American forest 

 is cut down, a very different vegetation springs up ; but it has been 

 observed that ancient Indian ruins in the Southern United States, 

 which must formerly have been cleared of trees, now display the 

 same beautiful diversity and proportion of kinds as in the surround- 

 ing virgin forest. What a struggle must have gone on during long 

 centuries between the several kinds of trees, each annually scattering 

 its seeds by the thousand ; what war between insect and insect — 

 between insects, snails, and other animals with birds and beasts of 

 prey — all striving to increase, all feeding on each other, or on the 

 trees, their seeds and seedlings, or on the other plants which first 

 clothed the ground and thus checked the growth of the trees ! Throw 

 up a handful of feathers, and all fall to the ground according to 

 definite laws ; but how simple is the problem where each shall fall 

 compared to that of the action and reaction of the innumerable 

 plants and animals which have determined, in the course of cen- 

 turies, the proportional numbers and kinds of trees now growing on 

 the old Indian ruins ! 



The dependency of one organic being on another, as of a parasite 

 on its prey, lies generally between beings remote in the scale of 

 nature. This is likewise sometimes the case with those which may 

 be strictly said to struggle with each other for existence, as in the 

 ^ase of locusts and grass-feeding quadrupeds. But the struggle will 

 almost invariably be most severe between the individuals of the 

 same species, for they frequent the same districts, require the same 



