Mammalia in the steppe biocenose [Les mammifères de la biocénose steppique].

Résumé

A rich fauna of herbivorous mammals is characteristic of all the steppes. These animals are a natural element of the steppe landscape and of the steppe biocenose. 2. The enormous majority of the steppe rodents dwell in more or less extensive and complicated burrows. One group of rodents spend all their life underground and procure their food by constant burrowing of passages (Siphaneus, Spalax, Ellobius and some others). The holes and the passages of the rodents penetrate to a depth of 4-5 meters. In piercing the soil and sub-soil with their galleries, throwing out upon the surface an immense quantity of earth from the deep lying layers, the rodents accomplish an enormous work. 3. This work is of great importance in the composition of the land surface, and especially in the formation of the soil and in the life of the vegetation. 4. The soil thrown out upon the surface by the rodents is, as a rule, less alkaline, richer in mineral salts and poorer in humus. 5. The vegetation upon the mounds thrown up by the numerous animals in the midst of the steppe, has usually a more desert, xerophytic character at first it contains many "weeds". 6. The earth thrown out upon the surface undergoes changes analogous to those which the soil of the surrounding steppe has passed through earlier. Simulatneoulsy with the process of soil formation, a change of vegetation takes place on the hillocks. Finally, the vegetation becomes like that of the places not dug up. 7. In he steppe occupied by rodents, both the superficial soil layers and the vegetation are not homogenous but varied. 8. Through the digging activity of the rodents, portions of the steppe continually revert to their original stage of development. The rodents postpone the natural succession of plant associations, and thereby assist in maintining for long periods the kind of vegetation to which they have become adapted. 9. The part which the hoofed animals play in the life of the steppe vegetation consists in stamping out the tussocks with their hoofs, destroying the dried up vegetation, and keeping down the too vigorous graminae. Their participation is likewise necessary in order to maintian the equilibrium inside the associations of the steppes. 10. In most conditions of nature, both groups of herbivorous mammals form the most active element of the biocenose. The evolution of the steppe plants associations, and of different species, has proceeded under the continuopus influence of these animals.