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. As a rule 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, 1 2 ; white 

 oak, 31; hickory, 30; wild cherry, 38; hazel, 33; total 401. He records 

 pests on trees of beech and maple forest as follows: beech, 92; sugar 

 maple, 19; pawpaw, 5; total, 116. 



1. 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 



