Vortrag, Wüstenränder multidimensional, Bayreuth: 13.01.2006 - 14.01.2006
Worldwide drylands have been shaped for millennia by grazing livestock and digging small mammals, nevertheless small mammals are often regarded as forage competitors for livestock. In Mongolia nomadic pastoralism has a long tradition and great economic importance. The carrying capacity for livestock therefore is of immediate interest. Due to high variability (e.g. of precipitation) in semi-arid ecosystems, field observations are too short to cover all significant states. Thus we developed a dynamic processes based model driven with data from a full-year field study and literature information. The model simulates pika and livestock densities as well as forage competition between both groups as a reaction to variable precipitation. Both groups can coexist because each has exclusive access to a forage resource unavailable to the other group: pika have the ability to bite down the vegetation deeper than livestock, while herders drive livestock to better pastures out of reach for pika when forage is scarce. Nevertheless, both groups react to the frequent periods of forage scarcity and indirectly interact via forage competition. Model results show that the drastic increase in livestock numbers after the transformation (1990s) was a result of more risky herding strategies supported by a series of years of above-average precipitation. The risky strategy took its toll in 1999-2002, when a large fraction of livestock starved. It can be concluded that the long-term carrying capacity has already been reached in the socialistic period and it cannot be expanded further in the future.