166 TERRESTRIAL CONDITIONS 
V. Quantity oF LIFE ON LAND (137) 
The quantity of life on land has been but little studied. While it is 
evident that some habitats have more animals than others, we have no 
exact data. Asarule the number of species is small in pioneer situations. 
While the number of individuals in some one or two species may be large, 
the grand total is probably not so large as in later stages. In forest 
development it appears from naturalistic observations that the number 
of both species and total number of individuals increases with age up 
to the oak-hickory stage, the maximum being in the oak-hickory stage. 
The beech and maple forest is qualitatively and quantitatively poor in 
animals. Felt (137) records pest species on the trees of the white-oak, 
red-oak, hickory forest as follows: Oak in general, 157; red oak, 12; white. 
oak, 31; hickory, 30; wild cherry, 38; hazel, 33; total 4or1. He records 
pests on trees of beech and maple forest as follows: beech, 92; sugar 
maple, 19; pawpaw, 5; total, 116. 
I. FOOD SUPPLY 
The food supply of land animals is in part dependent upon soil. All 
the chief principles governing the elementary food substance of plants 
and animals in water are given on pp. 65-68. Since all these processes 
are dependent upon water (as a solvent) and since soils at all times con- 
tain some water (116), the reader will easily apply most of the principles 
there stated to the soil problem. There is probably no kind of organic 
matter found that is not food for some animals. Some require plants 
or their juices, some decayed fruits, some wood, some living animals, 
and some carrion. Each stage of its decay, a dead plant or animal is 
food for some animal. 
Certain animals, usually plant-eaters, reproduce very rapidly and are 
preyed upon by many other animals. Mice, aphids, grasshoppers are 
examples (26). These form small centers about which many of the 
activities of a community rotate. The centers are indicated by the 
convergence of lines in Diagram 6. 
2. EQUILIBRIUM 
The balance in land communities is probably less perfect than in 
aquatic communities even under strictly primeval conditions. This is 
due to the fact that there are many small (feeding) groups of organisms. 
centering around each of several rapidly reproducing groups such as 
aphids, mice, and grasshoppers. It is accordingly probably possible for 
a land community to be out of adjustment in some particular corner 
