ECOLOGICAL SURVEYS 23 



ant question at once arises, as to whether the species 

 composition varies not only spatially but from year 

 to year in one place. We know that abundance of 

 the component species varies greatly, and it is to be 

 expected that as one falls below the level of density 

 which enables it to continue permanenth^, another 

 species may arrive and take its place. If this is so, 

 an ecological survey based on the results of ten years' 

 collecting might give a somewhat misleading picture 

 of the total number of species ever present in one 

 year. There is a suggestion of this phenomenon in 

 some of the surveys given in the table above, and the 

 question requires careful testing. 



For more extensive analysis of communities see Elton C. 

 (1946). J. Anim. Ecol. 1.5: 54-68; and for a discussion of 

 ecological survey in general, Elton, C. S. and Miller, R. S., 

 J. Ecol. (1954). J. Ecol. 42: 460-96. 



