without the maladjustment being felt as far as in an aquatic com- 
munity of corresponding magnitude. 
To illustrate the character of land communities in the matter of food 
supply and equilibrium we have chosen a number of prairie animals and 
constructed them into an arbitrary community. This community is 
graphically represented in Diagram 6. The arrows point from the 
animal eaten to the animal doing the devouring, many such relations 
being shown on the basis of actual published records. 
Bisgn 
Bison 
Deer mice 
C Vegetation ) 
Field*mic e 
May beetles Diptera 
Vegetation % 
sf 
eevils Crickets Grass SF 
Rattle snakes 
W Ground squirrels 
Pocket 
Gophers 
Dickcissels 
Prairie chickens 
Grasshopper Sparrows 
Vesper sparrows 
Horned 
larks 
Parasitic Hymenoptera 
Sawfly larvae 
Night hawks 
Bobolinks 
D1AGRAM 6.—Showing the food relations of land animals. Circles and ellipses 
inclose groups of organisms which are commonly eaten by the same animals, and 
groups eating similar food. Arrows point from the animals eaten to those doing the 
eating. For explanation see text. 
Vegetation 
Lepidopterous larvae 
Dry Vegetation 
Seeds Roots 
From the diagram we note that wolves destroy the bison. If for any 
reason the wolves increased, they would destroy so many bison that the 
bison would decrease because wolves were abundant. The greater 
destruction of mice in summer by the numerous wolves would cause a 
decrease of mice. Finally, wolves would decrease because of lack of big 
game in winter and mice in summer. This would give the bison and 
mice an opportunity to recover their former number and the whole 
chain of changes would be duplicated and a general equilibrium be 
