COMMLTNITY ORGANIZATION: STRATIFICATION 



469 



Herbivorous, cursorial, hoofed animals 

 are well-known examples of the prairie 

 grazing group. They form a noteworthy 

 list of ecologically replaceable or equiva- 

 lent species in both temperate and tropical 

 grasslands. Some of these stratal equiva- 

 lents are listed in Table 35, in which stra- 

 tal equivalence or replaceability is em- 

 phasized. It should be pointed out that this 

 tabular comparison does not differentiate 

 between tropical savannahs and temperate 

 prairies. These grassland community types 

 are touched upon later in tliis chapter and 

 discussed in more detail in the chapter on 

 the biome. In the second place, this table 

 does not differentiate between diurnal and 

 nocturnal species. Such periodism and its 

 far-reaching influence comprise the subject 

 matter of a separate chapter. Attention is 

 directed, however, to the close stratal con- 

 gruence within the grassland communities 

 of the world, which in turn reemphasizes 

 the essential similarity in structure of such 

 communities. 



The majority of the cursorial, herbivo- 

 rous hoofed mammals mentioned in the 

 table occur in large aggregations. Through 

 their grazing activities they compete direct- 

 ly with agricultural man and other prairie 

 animals, for example, the meadow mice 

 (Microtus), which may populate grass- 

 lands in excess of fifty mice per acre 

 (Hamilton, 1940). The combined action of 

 all these herbivorous groups is a large-scale 

 intracommunity cooperative influence re- 

 stricting the vegetational stratum within 

 certain growth hmits. On the other hand, 

 these herbivorous grassland groups are 

 limited in their dispersal and increase 

 through the amount and distribution of 

 naturally developed prairie vegetation, and 

 that introduced and cultivated by man 

 (wheat, barley, rye, oats, corn). The dom- 

 inance of agricultural man in prairie com- 

 munities varies with the geographic location 

 of a particular grassland community, his 

 sociological emergence, and the period of 

 history examined. 



The responses of herbivorous mammals 

 to the primary vegetational zone of the 

 grassland, the herbaceous stratum, is re- 

 sponsible for at least three widespread 

 biotic effects. 



The first is the presence of predators 

 in suflScient numbers to maintain a biotic 

 balance with their food supply (p. 370). 



They consequently regulate the herbivo- 

 rous population in part, and in part have 

 their own numbers regulated by the abun- 

 dance of their food, in the same general 

 way in which the herbage and herbivorous 

 population exert a reciprocal effect (p. 

 706). These predators include reptiles, 

 birds, and mammals feeding chiefly upon 

 insects, rodents, and ungulates. Probably 

 the most widely known of these carnivores 

 are the predaceous cats and dogs (Table 

 35). These are typically adjusted for stalk- 

 ing or running down their particular foods 

 (p. 242), either as solitary hunters or in 

 hunting packs, and either in the active or 

 inactive period of their prey, depending 

 upon the activity cycle of both the preda- 

 tor and prey (p. 544). The general rela- 

 tion between the number of herbivorej: 

 and the number of predators within u 

 given grassland community is shown in 

 Table 35. For example, in the mammals, 

 the rich grassland herbivore population of 

 Africa is paralleled by an equally rich 

 predator population. In contrast, Australian 

 plains have fewer native predators and 

 fewer large native herbivores. This latter 

 instance, in which the marsupial popula- 

 tion has radiated and flourished in the 

 absence of effective competition, is an il- 

 lustration of how isolation may affect the 

 stratal composition of a community (p. 

 666). 



Herbivorous hoofed animals of grass- 

 land, in the second place, contribute to 

 the invertebrate life of the floor and sub- 

 terranean strata by their dung. This affords 

 sustenance directly to coprophagous insects, 

 and indirectly to the parasitic and preda- 

 ceous insects that feed in turn upon them. 

 The relative importance of these dung-in- 

 habiting animals is not apt to be appre- 

 ciated if the methods of assay do not take 

 animal droppings into account. The num- 

 ber of species and individuals inhabiting 

 ungulate dung is high in unwooded pas- 

 tures—for example, in central Illinois 

 (Mohr, 1943) and New Jersey (Wilson, 

 1932), where dung is provided by sheep 

 or cattle droppings. 



The scavengers feeding upon the dung 

 include scarabaeid beetles of the subfami- 

 lies Geotrupinae, Aphodiinae, and Cop- 

 rinae, and numerous flies (Cryptoliicilia, 

 Haematobia, Sarcophaga, and Sepsis). 

 These flies and beetles oviposit on the 



