ECOLOGICAL SUCCESSION 23 



income of water, and extremes of environment are avoided. 

 This is, of course, only a rough generalisation and applies 

 especially to temperate regions, but it explains v^hy w^e often 

 get seres on very different kinds of bare areas converging 

 towards the same final climax. 



7. The account of this subject given above is necessarily 

 brief, and a much fuller account is given by Tansley in his 

 book Practical Plant Ecology}^ which is essential to the work 

 of all animal ecologists. Clements has treated the whole 

 subject in stupendous detail in his monograph Plant Sue- 

 cesston,^^ which is illustrated by a very fine series of photographs 

 of plant communities. 



Let us now consider a few examples of succession in animal 

 and plant communities. It is clearly impracticable to take 

 more than a few species as examples of changes in whole 

 communities, and naturally the exclusives afford the most 

 striking ones. There are several ways in which animal suc- 

 cession can be studied. The best way is to watch one spot 

 changing over a series of years and record what happens to 

 the fauna. This is the method least practised, but the most 

 likely to lead to productive results, since we stand a good 

 chance of seeing how the structure of the communities is 

 altered as one grades into another. Yapp 3i says : '* We may 

 perhaps regard the organisms, both plants and animals, occupy- 

 ing any given habitat, as woven into a complex but unstable 

 web of life. The character of the web may change as new 

 organisms appear on the scene and old ones disappear during 

 the phases of succession, but the web itself remains." It is 

 just the changes in this " web " about which we know so little 

 at present, and that is why study of the actual changes will 

 always be the most valuable. 



8. One of the most interesting and clear-cut examples of 

 succession, recorded by Ritchie,^^^ is so striking that it has 

 been often quoted, and is worth quoting again here. He 

 describes the manner in which a typical heather moor in the 

 south of Scotland, with its normal inhabitant, the red grouse 

 {Lagopus scoticus), was converted in the short space of fifteen 

 years into a waste of rushes and docks, inhabited by a huge 



