COMMUNITY ORGANIZATION: STRATIFICATION 



473 



stratum, often with introduced species. 

 Such introductions should be stratal equiva- 

 lents of the original species. Table 36 hsts 

 the U. S. Department of Agriculture's de- 

 Uberate imports for the control of soil ero- 



tatomidae, Coreidae, Lygaeidae, Cicadelh- 

 dae, Psyllidae, Aphididae), many species 

 of which feed on this stratum of plants. 



Grasslands support large populations of 

 these macroscopic invertebrates, the ma- 



Table 36. Herbaceous Equivalents Used in Soil Erosion Control (Reorganized from U. S. 

 Department of Agriculture Yearbook, 1938) 



sion according to the region of their 

 nativity. 



This vegetation, varying in height and 

 density of stand, scorching in the hot, dry 

 summer or billowing in the wind, gives a 

 characteristic aspect to the community. Its 

 ecological equivalents or their cultivated 



jority of which are directly or indirectly de- 

 pendent upon the herbaceous sbatum for 

 food. For example, Morris (1920) found 

 3,586,088 insects per acre of permanent 

 pasture in Cheshire, England. A compari- 

 son of several investigations is given in 

 Table 37, in which it is of interest to note 



Table 37. Pasture Populations of Macroscopic Invertebrates 



Locahty 



Cheshire, England 



Barneveld, New York 



Pt. Cangrejos, Puerto Rico 



Animals per 

 Square Foot 



82 



68 



110 



Animals per 



Square Meter 



(Recalculated) 



(Estimate) 



869 



720 



1166 



Author of 

 Study Cited 



Morris, 1920 

 Wolcott, 1937 

 Wolcott, 1924 



replacementij support numerous floor herbi- 

 vores (grasshoppers and rodents). In ad- 

 dition, the population of this grassy 

 stratum per se is large and varied, consist- 

 ing chiefly of herbivorous bugs, beetles, 

 and lepidopterous larvae (Hayes, 1927). 

 The bugs considered alone include a note- 

 worthy number of important families (Pen- 



that there is a small suggestion that tropi- 

 cal pastures have a higher population den- 

 sity than temperate pastures, but there are 

 insufficient data available to test the statis- 

 tical significance of this point. 



Where land is put into cultivation 

 by man, its herbaceous stratum is shielded 

 from natural competition and becomes dom- 



