Geography Reference
In-Depth Information
Figure 7.6 Pika burrow density as a function of vegetation height.
70
60
50
40
30
20
10
0
0
10
20
0
40
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Vegetation Height (%)
From: Fan et al. 1999
Source: Adapted from Fan et al. 1999.
were, like so many other rodents in agricultural China, simply “harmful.” Thus, begin-
ning in 1958—the very year in which the Maoist onslaught upon nature was building to a
crescendo—governments began supporting “rodent control” on the grasslands. Over such
large areas, poisoning was the only method seriously considered for pikas. In the early
years, zinc phosphide was the preferred rodenticide, but later fluouroacetate (also known
as Compound 1080), anti-coagulants such as diphacinone, and even bacteria-produced
toxins such as botulinin C were used, as they were found to be superior in either killing
efficiency or in minimizing secondary toxic effects. 83 By 1990, a cumulative total of some
208,000 km 2 had been subject to such poisoning, usually carried out by county-level
agricultural, grazing, or forestry bureaus.
Although both species were successfully reduced locally by such poisoning, these
energetic efforts succeeded neither in eliminating either species entirely, nor—if govern-
ment statistics are to be believed—in improving grassland conditions on a large scale. 84
This should not have come as a big surprise: both species, in common with most small
mammals, have prodigious capacity to recover quickly from declines, and thus continu-
ous, long-term application of rodenticides would have been necessary to prevent popula-
tion recoveries. 85 As well, poisoning, particularly during early years when unselective
agents were used, most likely also killed large numbers of animals that naturally preyed
on pikas or rodents, thus weakening natural control. 86 Further, it emerged that, at least
in some places, pikas and zokors competed with each other for resources: kill enough
pikas (usually the initial target, and by far the easier of the two to reduce because of
 
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