Cox G W, Allen D W
Department of Biology, San Diego State University, 92182, San Diego, CA, USA.
Oecologia. 1987 May;72(2):207-210. doi: 10.1007/BF00379269.
We measured soil translocation due to the tunneling of valley pocket gophers (Thomomys bottae) in a Mima moundfield at Miramar Mounds National Landmark, San Diego, California, from December, 1984 through December, 1985. We placed 1-l soil plugs containing 20 11-g iron pellets into pocket gopher tunnels at locations between mound tops and points about one mound radius beyond mound edges. After about 4-10 d, sites to which the marker-containing soil had been translocated were located with a metal detector and the horizontal and vertical displacements measured. Between 1 October and 15 May (the cooler, wetter portion of the year), pocket gophers removed an average of 63% of the experimental plugs and moved an average of 38% of the markers that we recovered. From 15 May through 1 October (the hotter, drier portion of the year), only 32% of plugs were cleared and 12% of the recovered markers were moved. On average, markers that were moved were displaced 41 cm moundward and 4.9 cm upward in elevation. The intensity of moundward translocation increased with distance from the mound center. At a distance of 0.5-1.0 mound radius beyond the edge of the mound, the moundward translocation tendency averaged 71 cm. The intensity of moundward translocation was also inversely related to maximum mound height. These observations provide strong support for the fossorial rodent hypothesis of Mima mound origin, and constitute a first step in development of a mathematical model of mound formation.
1984年12月至1985年12月期间，我们在加利福尼亚州圣地亚哥米拉马尔土墩国家地标区的一个米马土墩群中，测量了由于谷地囊鼠（Thomomys bottae）挖掘洞穴而导致的土壤迁移情况。我们将装有20颗11克铁丸的1升土壤塞放入囊鼠洞穴中，放置位置在土墩顶部与土墩边缘外约一个土墩半径处的点之间。大约4 - 10天后，用金属探测器定位含有标记物的土壤被迁移到的地点，并测量水平和垂直位移。在10月1日至5月15日（一年中较凉爽、湿润的时段），囊鼠平均移走了63%的实验土壤塞，并且平均移动了我们找回的38%的标记物。从5月15日至10月1日（一年中较炎热、干燥的时段），只有32%的土壤塞被清理，找回的标记物中有12%被移动。平均而言，被移动的标记物向土墩方向位移了41厘米，海拔上升了4.9厘米。向土墩方向的迁移强度随着与土墩中心距离的增加而增大。在土墩边缘外0.5 - 1.0个土墩半径的距离处，向土墩方向的迁移趋势平均为71厘米。向土墩方向的迁移强度也与土墩的最大高度成反比。这些观察结果为米马土墩起源的穴居啮齿动物假说提供了有力支持，并构成了建立土墩形成数学模型的第一步。
