Reconstructing past population processes with general equilibrium models: House mice in Kern County, California,

Transcription

1 Reconstructing past population processes with general equilibrium models: House mice in Kern County, California, Seong-Hee Kim,* John Tschirhart,*, Steven W. Buskirk** *Department of Economics and Finance, University of Wyoming, Laramie, WY 82071, USA ** Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA Ati Article history: Received 30 January 2007 Received in revised form 14 June 2007 Accepted 29 June 2007 Published on line 6 August 2007

2 The Invasion On January 10, 1927, the Museum of Vertebrate Zoology, University of California received the following message from the town of Taft in Kern County, California: Talk about 'nothing new under the sun.' Well there is. The highway between Panama and Taft is literally plastered with dead mice, and millions of them alive chasing across the highway; it's sickening. The mice were house mice (Mus musculus), and the latest outbreak followed two others that began in November, The affected area was about seventeen miles in diameter and centered on the dry bed of Buena Vista Lake. The area north and south of the lake were reported as barren hills with little human habitation. West of the lake there were small towns and camps, and east of the lake and in the lakebed itself, the land was cultivated in barley, wheat, corn and cotton. The crops were thought to provide food and shelter for the mice, but after the autumn harvest and sheep grazing, little food and shelter remained and the mice began a radial migration from the lakebed. From population estimates: the number of mice was almost unbelievable. Hundreds of mice could be seen at any given time. In the more dense areas were 17 mice per square yard, and projecting this was 82,280 mice per acre or 2468 pounds of mice per acre. About 15% of the mice were the much larger meadow mice (Microtus californicus), and they were mostly in overcrowded burrows whereas the house mice were virtually everywhere. People in the nearby towns were interrupted in their sleep by mice scurrying across their bedding, and in the mornings mice were frequently in clothing and shoes. The major highway was slushy with dead mice and the stench arising from the voided body excrements is highly offensive and nauseates many persons. The farmers and businesses in the area spread poisons and in one barn and two tons of mice were killed on one day. On January 15, 1927 a headline in the Los Angeles Times stated: An Army of Field Mice Kill and Eat Sheep at Taft. The story concerned one unlucky sheep that was confined to a pen and unable to escape. Beyond the emotional stress on the residents of Kern Country, the actual damage that the mice were seen to do included the destruction of quantities of stored grain; the reduction of large stacks of hay; the destruction of foodstuffs, clothing, bedding, linen, etc., in houses; and the gnawing of holes through the floors and walls of frame buildings. The estimated damages in 1926 after harvest was approximately 10,000 sacks of barley, more than 10,000 sacks of milo corn, and an even greater amount of feed corn. The value of agricultural crops lost was estimated at $125,000 and the other damages such as the destruction of stores, horse feed material, clothing, etc. was around $21,000 in 2003 dollars. The campaign to eradicate the mice went into high gear on January 22 when Stanley Piper from the U.S. Biological Survey arrived to map out a plan of battle against what he estimated to be more than 100 million mice (2000/acre). Eschewing the flute approach used by the Pied Piper of Hamelin, this Piper had a crew of twenty-five men who laced forty tons of alfalfa with strychnine. By the end of February they declared success in what was labeled the worst rodent infestation in U.S. history.

3 Kern County Ecosystem crops house mice Sun grass vole (domestic mice) predators

4 Figure 1 a Predator resonse 2% Native mice response 12% Plant disturbance 20% year Grass Native mice Predator Fig 1. Effect of 20% in plant population

5 Predator disturbance 20% Native muce response 0.05 % Grass response % year Grass Native mice Predator Fig. 1b. Effect of 20% disturbance in predator population

6 Predator consumption Predator expenditures Native mouse consumption Native mouse expenditures Plant biomass Plant expenditures Year Fig 2. Relationships between energy exp. and consumptions or plant sizes. Note slight lag.

7 Fig predators Predators extinct plants native mice predators 86,878 native mice 88,300 native mice Plants Year Fig. 3. Model-simulated behavior of the Kern County, California ecosystem with no house mice and humans hunting predators.

8 a Fig. 4 plants house mice native mice predators 64 predators 41 predators 78 predators 16 native mice 86,872 native mice 517,000 house mice (peak) 226, ,400 house mice 2 house mice 87,000 house mice Plants Year Fig. 4. Model-simulated behavior of the Kern County, California ecosystem with introduced house mice, but no humans hunting predators.

9 b Fig 4 58 predators 31,400 native mice 56 predators 20,700 native mice 242,000 house mice 89,000 house mice plants Year

10 Fig. 5. Model-simulated behavior of the Kern County, California ecosystem with introduced house mice and humans hunting predators. 41 predators Hunting begins 56 predators Predators extinct native mice 889 native mice 23,000 native mice 502,610 house mice (peak) Native mice extinct 2housemice 198,000 house mice Plants Year

11 Table 3. Varying the rate of hunting when the invasion begins in 1876 and human hunting of predators begins in 1906 Yearly growth in rate of hunting Year of predator extinction Year of peak house mouse N Peak house mouse N no hunting no extinction No predators at outset NA No irruption No oscillations