178 



ANIMAL ECOLOGY 



long to include on the diagram. It is also sometimes useful 

 to include the relative sizes of the different animals, but here 



Fig. 13. — The diagram shows part of an animal community in Canada, 

 and illustrates the method of including food-chains and the size of the 

 animals in the same diagram. (The figures are lengths of the animals in 

 millimetres — average for both sexes, tip of nose to base of tail.) This 

 diagram should be compared with that in Fig. 12, giving the length of 

 the period of fluctuation of the animals. (From Elton. ^*) 



one is usually hampered by lack of data or by the difficulty of 

 finding a standard to which animals of different shapes can 

 be referred. 



