Plain Predictions: An Industrious Native Vole and Overgrazing by Livestock Are Making a Desert of Inner Mongolia's Once Fertile Grasslands. Wendy Pyper Outlines Efforts to Arrest the Transformation
Pyper, Wendy, Ecos
Fifty years ago, sweeping vistas of waist-high grass were the trademark of Inner Mongolia. But today, stubbles of grass and weeds carpet much of the landscape, and wind erosion speeds desertification.
This transformation of China's northern-most province from productive to degraded grassland is a result of livestock overgrazing and surges of small, burrowing mammals. Among them is the disarmingly cute native mammal known as Brandt's vole.
The Brandt's vole thrives amid short, overgrazed pastures, digging enormous burrows, and storing food for the harsh Mongolian winter. A female vole can raise some 25 young in its 18-month life span.
In most years vole numbers are low enough not to cause problems, but occasionally populations erupt.
When this happens, the combination of voles and livestock depletes the palatable plants, leaving the topsoil exposed to fierce, spring winds originating in Siberia.
Dr Roger Pech and Dr Stephen Davis from CSIRO Sustainable Ecosystems are trying to discover what conditions trigger these troublesome eruptions.
Pech and Davis, both ecologists and mathematical modellers, are working with a group of Chinese rodent ecologists to develop a model for predicting vole outbreaks. The model uses 50 years of vole population data collected by Chinese ecologists, and correlates eruptions with regional rain and snowfall, and the Southern Oscillation Index (SOI).
Davis says there is evidence that moderate to dry conditions tend to favour the vole. Low precipitation usually means shorter grass, which may in turn enable voles to see and avoid predators and communicate visually with other voles. In Inner Mongolia, drier weather appears linked with consistently high and positive values of the SOI, suggesting trends in this climatic index could be used to forecast outbreaks of voles.
Pech says one of the difficulties with predicting eruptions, however, is that an outbreak doesn't always occur under the `right' climatic conditions. This is similar to the problem of predicting when plagues of house mice will occur in the wheatbelt of south-eastern Australia.
Forecasting vole outbreaks is further complicated by the effects of livestock grazing, and possibly by diseases, such as Bubonic plague, which vole populations harbour. Pech says future predictive models may include livestock grazing, and factors that determine the growth and senescence of pasture. But at this stage insufficient data exist to include the effects of disease on vole abundance.
Pech and Davis are also working with CSIRO reproductive and molecular biologists Dr Lyn Hinds and Dr Chris Hardy to compare the effects of various control methods on the vole population.
Brandt's vole is controlled using poison baits, which are not species specific and endanger both predators of the vole and other small, native mammals.
Hinds and Hardy have been working on a fertility control method for foxes, rabbits and mice, which acts on the animals' immune systems, and could be adapted for Brandt's vole (see Domesticus interruptus, Ecos 104). The sterilising vaccine, known as immuno-contraception, would be delivered in non-toxic baits to provide a new, species-specific and humane control option for voles.
Pech, Davis and their Chinese colleagues used data from a three-year study of vole survival and fecundity to compare, theoretically, the effects of poisoning and fertility control. …