[Dynamics of rodent community and populations in Kalmyk semideserts under decreasing pasture load and increasing...

Today, pastural ecosystems of the Kalmyk Republic demonstrate progressive regrowth dynamics, which is explained by a sharp decrease in grazing load and the onset of a new humidification cycle in the Caspian Lowland. By the mid-1990s, the sparse and poor desert vegetation with a significant proportion of ephemerals, characteristic of these ecosystems in the 1980s, had been substituted by highly productive tall-grass communities typical of steppes. Under such conditions, corresponding changes in the distribution and abundance of rodents could be expected. These parameters were assessed in different types of habitats in Chernye Zemli (the Kalmyk Black Lands) from 1980 to 1983 and from 1993 to 1997. Rodents were captured in live traps distributed over permanent test plots and in crush traps arranged in lines. The results showed that the population of midday gerbils did not change significantly during this period, although their favorite open habitats considerably decreased in area. The abundance and range of tamarisk gerbils noticeably increased, whereas those of little sousliks continued to decrease, contrary to our expectations. Thus, a rapid progressive succession in plant communities did not cause the corresponding change (of similar rate and extent) in the structure of rodent community. The difference between the observed and expected results provides evidence that rodent populations are somewhat "inert" in their response to changes in environmental conditions, and their development is relatively independent of these changes, but is contingent upon the state of populations in the past (i.e., the history of colonies).