52 ANIMAL ECOLOGY 



some species more than others. Some of the remarkable 

 resuhs of " rabbit action " on vegetation may be read about in 

 a very interesting book by Farrow, i^ Since rabbits may influ- 

 ence plant communities in this way, it is obvious that they have 

 indirectly a very important influence upon other animals also. 

 Taking another Hne of investigation, we might follow out the 

 fortunes and activities of the green woodpeckers, to find them 

 preying on the big red and black ant (Formica rufa) which 

 builds its nests in woods, and which in turn has a host of other 

 animals linked up with it. 



If we turned to the sea, or a fresh- water pond, or the inside 

 of a horse, we should find similar communities of animals, 

 and in every case we should notice that food is the factor which 

 plays the biggest part in their lives, and that it forms the 

 connecting link between members of the communities. 



3. In England we do not realise sufficiently vividly that 

 man is surrounded by vast and intricate animal communities, 

 and that his actions often produce on the animals effects which 

 are usually quite unexpected in their nature — that in fact man 

 is only one animal in a large community of other ones. This 

 ignorance is largely to be attributed to town life. It is no 

 exaggeration to say that our relations with the other members 

 of the animal communities to which we belong have had a big 

 influence on the course of history. For instance : the Black 

 Death of the Middle Ages, which killed off more than half the 

 people in Europe, was the disease which we call plague. Plague 

 is carried by rats, which may form a permanent reservoir of 

 the plague bacilli, from which the disease is originally trans- 

 mitted to human beings by the bites of rat fleas. From this 

 point it may either spread by more rat fleas or else under certain 

 conditions by the breathing of infected air. Plague was still 

 a serious menace to Hfe in the seventeenth century, and finally 

 flared up in the Great Plague of London in 1665, which swept 

 away some hundred thousand people. Men at that time were 

 still quite ignorant of the connection between rats and the 

 spread of the disease, and we even find that orders were given 

 for the destruction of cats and dogs because it was suspected 

 that they were carriers of plague. ^^^ And there seemed no 



