ECOLOGICAL SURVEYS 19 



surveys comparable. But certain tacts stand out 

 clearly. First the comparatively low number of 

 species which make up any animal community of a 

 major habitat such as a wood, a heath, a coral reef, 

 or a river Taking the figures at their face value, 

 we observe that the highest recorded number of 

 species is 173, while the most frequent values lie 

 between 60 and 140. This generalization is of value, 

 since it indicates roughly the framework within which 

 an animal community is organized. We may expect 

 to find usuall}^ not more than 200 species of animals 

 (taking forms visible without a microscope). In some 

 rich marine habitats, and likewise in woods and even 

 more so in tropical forests, we may expect to find 

 a good many more species than this. Probably the 

 number of species of animals in a community which 

 has well-defined vegetation usually exceeds but does 

 not greatly exceed the number of plant species found 

 there. For example, Walton found 69 species of 

 algae on the coast of Cardigan Bay, and 156 species 

 of animals. The number of plant species found on 

 chalk grassland by Tansley and Adamson (1926) was 

 151, but only from 24 to 75 occurred at each station 

 studied. The number of animals on grassland almost 

 certainly exceeds a hundred, as shown by the work 

 of Morris and Cameron. But, in the high Arctic, 

 plant species outnumber animals (North Spitsbergen 

 at one station, 52 species of plants, and only 27 

 species of animals, Summerha^^es & Elton, 1928). 

 In tropical rain forest the scales would be heavily 

 weighted the other way. 



We seem then to be in a position to generalize as 

 follows from the ecological survey work so far done. 

 The number of species collected by present methods 

 of surveying in an animal community of any major 

 habitat does not usually exceed about 150 in 

 temperate regions. In the high Arctic the number 

 is much less, also on certain very unfavourable 

 habitats further south. But the number of species 



