Effects of density-dependence and climate on domestic sheep population in history and current Mongolia grassland

分类： 生物学 >> 生态学 提交时间： 2017-05-04

Ang Li

摘要： The combined effects of climate and density-dependence on ungulate population were widely detected, which played the critical role in maintaining sustainability of rangeland ecosystems. But, previous studies in Mongolia plateau seldom considered the density dependent effect of the domestic animals, but mainly focused on the impacts of natural hazards. In order to fill this knowledge gap, we selected ten long-term sheep population series from the eastern part of Mongolia plateau and detected the density dependent effects. Three kinds of methods were independently employed in this study, i.e. the demographic parameters analysis, statistic tests, and the model selection method. The density dependence was detected by all methods during the nomadic period of 1962-1979. It found that three populations were density dependence. The seven other populations were only regulated by density dependent effect during normal winters, and just controlled by climate during harsh winters. The limitation of density dependent effect can explain the reason of why herdsmen migration distance positively correlated with the size of their herds. Therefore, there were two types of natural pushing force to drive nomadic people migration, one was the natural hazard which was widely accepted, and the other was the density dependent effect. Especially, “pushing off of density dependence” can explain the reason why Genghis Khan’ rise and conquest happened during the medieval climatic optimum, when the natural hazard was less than other period in the record history of Eurasian. On the other hand, the study showed that the climate effect on population had weakened and the density dependent effects disappeared during the sedentary period. This finding is the reason of why the sheep population had showed a continued growth trend and caused “overgrazing” problem. Our results indicated that the disappearing of natural negative feedbacks had driven the ecosystem regime to shift from the “animal population is low but ecosystem is spontaneously sustainable status” into “animal increased rapidly but vegetation degenerated status” during the social change of sedentary in the Mongolian plateau.

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