472 



THE COMMUNITY 



dung, and their larvae feed upon this rich 

 source of energy. In other instances the 

 coprine scavengers {Canthon, Copris, 

 Onthophagus, and Scarabaeus) usually 

 first cut out portions of the dung and 

 roll these balls either into a protected niche 

 in the floor, or bury them deeply in the 

 subterranean stratum before oviposition. In 

 either case these coprophagous insects are 

 eaten in their immature stages by a variety 

 of predators, including histerid and staphy- 

 linid beetles. 



In addition, the mature and immature 

 scavenger flies and beetles are sources of 

 transportation or food for the essential 

 coprocolous bacteria, myriads of larval, 

 nymphal, and mature mites (Parasitidae), 

 and parasitoid Hymenoptera (Figitidae). 



During the period when ungulate drop- 

 pings retain their individuality, passing 

 from a moist irridescence to a hard, dry 

 chip (p. 568), they represent insular areas 

 with coprocole populations, concentrically 

 stratified, on the grassland floor. Later the 

 matrix of these islands becomes incorpo- 

 rated into the subterranean stratum by 

 leaching and absorption through weather- 

 ing and erosion. 



Droppings of the larger animals, while 

 supporting large populations, are directly 

 affected by chemical conditions (host diet 

 and physiological state) and physical con- 

 ditions (light intensity, air temperature, 

 precipitation, and evaporation). Both physi- 

 cal and chemical conditions on the floor 

 about the droppings, and within its matrix, 

 affect the bacteriological industry carried 

 on within the dung. These three influences 

 are important in regulating the activity 

 and substratification of the coprocolous bio- 

 coenose of the grassland community. 



Fly and beetle scavengers that once 

 thrived upon bison and prongbuck dung of 

 the North American plains now feed upon 

 the excrement of our domestic cattle 

 (Hayes, 1929). Some idea of the impor- 

 tance of dung to the grassland community 

 may be had by a brief examination of the 

 herbivore population. Seton (1909) esti- 

 mated that at one time the North Ameri- 

 can prairie was inhabited by one bison per 

 20 acres. Henry and Morrison (1923) 

 found that beef cattle prodxice 52 pounds 

 of dung per 1000 pounds of live weight 

 per day. If we estimate the average hoofed 

 mammal of the steppe at 500 pounds, and 



the average daily dung component at 25 

 pounds, then the hypothetical minimum 

 dung component from large ungulates 

 alone works out at a little more than 1 

 pound of dung for each acre of grassland 

 per day. If we assume an equal amount 

 for all other grassland animals, we would 

 have, at a conservative estimate, 2 pounds 

 per day per acre. Assuming that half of 

 this amount is blown or washed away, eaten 

 by coprophages, or otherwise made un- 

 available for direct fertilization of the sub- 

 terranean stratum, the amount remaining 

 would be not less than 100 pounds of dung 

 per acre for the growing season of grass- 

 lands. 



In the third place, the grassland floor her- 

 bivores, through their droppings, further in- 

 fluence the community. When one considers 

 grassland from a general point of view, the 

 amount of manure available for fertilizer 

 affects the growth and vigor of the her- 

 baceous stratum more than is usually ap- 

 preciated. Consequently, in addition to 

 extracommunity fixation of atmospheric 

 nitrogen (p. 190), we have intracommu- 

 nity regulation of plant growth directly, and 

 animal growth directly and indirectly 

 through humus formation, and directly by 

 increasing the fertility of the soil. 



The herbaceous stratum of the grassland 

 communities varies from a relatively close 

 carpet of green, soft, broad-leaved grasses 

 and other perennial herbs to coarse, hard, 

 narrow-leaved stands, and similarly varies 

 in height from 6 to 120 inches. Dominant 

 stratal species belong to such genera as 

 Andropogon, Bouteloua, Koeleria, Agropy- 

 ron, Stipa, Calamovilfa, Panicum, Car ex, 

 Artemesia (Warming, 1909; Carpenter, 

 1940a; Hanson and Whitman, 1938), which 

 penetrate deeply into the subterranean 

 stratum and are adjusted to desiccation. In 

 addition, steppes have vernal plants with 

 bulbs or tubers (Liliaceae) and short-lived 

 annuals. 



When man disturbs the natural structure 

 of grassland beyond the limit of commu- 

 nity repair, as in excessive and unscien- 

 tific cultivation or overgrazing, wind and 

 water erosion may remove the floor stra- 

 tum completely and partially destroy 

 the subterranean stratum. In such cases it 

 is of immediate interest to note that one of 

 the most effective measures to combat ero- 

 sion is the planting of a new herbaceous 



