660 The Outline of Science 



and /), the hedgehogs that devour the slugs, the lapwings that 

 prey upon the wireworm, the lady-birds that check the prolific 

 green-fly, and the ichneumon flies that lay their eggs in 

 caterpillars. 



Reference has already been made in the article, EVOLUTION 

 GOING ON, to Dr. James Ritchie's masterly book, The Influence 

 of Man on Animal Life in Scotland (1920), wherein it is shown 

 with scholarly precision what changes have been wrought in a few 

 thousand years by man's domesticating and destroying, intro- 

 ducing and eliminating, preserving and cultivating. The out- 

 standing lesson is surely that no creature lives or dies to itself, 

 that the consequences of every move are not only direct but 

 far-reaching till the game is done. 



The Story of the Gullery 



From one we may learn all, so we take from Dr. Ritchie's 

 book a single instance of the intricate interlinking of lives. It 

 concerns a colony of black-headed gulls (Larus ridibundus) , 

 which established itself on the White Moss, near West Linton, in 

 Peeblesshire. In 1890 the Moss was a typical heather moor, with 

 peat and moisture underneath. In 1892 or 1893 a few pairs of 

 gulls came to nest on the Moss, and were encouraged; in 1897 

 there was a populous colony; in 1904 the number was estimated 

 at 1,500 to 2,000 pairs. The vegetation round about the colony 

 underwent a remarkable change; the heather was replaced by 

 coarse grass, and that by rushes, and these by a forest of docks. 

 These changes in the flora were due, of course, to the faunistic 

 gull-invasion. The poor soil, which only the symbiotic heather 

 could make anything of, was fertilised by food-refuse and excreta 

 from the gullery. Moreover, the puddling of the surface ground 

 by the thousands of busy webbed feet, and the surface accumula- 

 tion of crowded nests, meant a retention of superficial water. 

 At all events, the peat bed with its concealed and deep moisture 

 was transformed into a surface marsh. 



