4 88 CHAINS OF CIRCUMSTANCE 



the increase, in numbers and variety, of the animal inhabi- 

 tants of Scotland. 



INFLUENCES TENDING TO REDUCE ANIMAL LIFE 



Two main lines of action have told severely upon the 

 original fauna of Scotland. The first is patent in its direct- 

 ness the deliberate destruction of creatures, whether for 

 food or profit or because they threatened to destroy the 

 security of man or of his domestic stock. The former lost 

 to us the Great Auk, the latter the Wolf and many beasts 

 and birds of prey. The second group of influences, indirect 

 in their incidence, is associated with the disturbance of the 

 haunts of wild creatures, and can be traced to the needs of 

 cultivation and the demands of advancing civilization (see 

 Fig. 86, p. 484). The former banished the creatures of the 

 moorland when fields were tilled, and the birds and creeping 

 things of the marsh when swamps were drained ; both agri- 

 culture and civilization, but especially the latter on behalf of 

 its growing industries, contributed to the destruction of the 

 forest and in consequence to the disappearance of the wood- 

 land animals; and civilization is responsible for the ill effects 

 of the pollution of rivers and of the obstacles placed in the 

 way of migrant fishes. 



It need not happen that the creatures against which 

 man sets his hand, unwittingly or with intent, necessarily 

 become exterminated. Adverse influences are as clearly 

 marked by simple reduction in numbers, or by a gradual 

 drawing in of the outposts of a species, so that its territory 

 becomes less. 



It must not be supposed that these influences making for 

 the increase or decrease of a species are simple in their work- 

 ings. So far from being mutually exclusive they are highly 

 involved, and the final tendency in the history of any creature 

 must be interpreted with due regard to the conflicting influences 

 which have played upon it. Take, for example, the case of 

 the Stoat. On the one hand its numbers have been reduced, 

 directly, by slaughter for the value of its skin, and on 

 account of its depredations on game, and indirectly by the 

 destruction of woods and its safe retreats. On the other 

 hand its numbers have tended to increase because of the 



