Malmquist Mats
Department of Zoology, University of Uppsala, Box 561, S-751 22, Uppsala, Sweden.
Oecologia. 1986 Sep;68(3):344-346. doi: 10.1007/BF01036736.
Pygmy shrewsSorex minutus occur allopatrically in Ireland, the Outer Hebrides and Gotland in Sweden, and sympatrically with common shrewsS. minutus on the European mainland and in England. Competition theory redicts higher population density in allopatric populations as a consequence of relaxed competition. Here this prediction is tested by comparing allopatric populations of pygmy shrews in the Outer Hebrides and in Gotland with sympatric populations on the Swedish mainland. Population densities were higher in allopatry than in sympatry. Lower summed densities in allopatry, which is predicted by niche theory, was found on the Outer Hebrides, but not on Gotland. Size distributions of carabids, which are important food items, could not explain the differences in population densities. Since both avian predators and snakes are present in all areas, population density of pygmy shrews during autumn in concluded to be regulated primarly by competition with common shrews in areas of sympatry.
侏儒鼩鼱（Sorex minutus）在爱尔兰、外赫布里底群岛和瑞典的哥特兰岛呈异域分布，在欧洲大陆和英格兰则与普通鼩鼱（S. minutus）同域分布。竞争理论预测，由于竞争缓和，异域分布种群的种群密度会更高。在此，通过比较外赫布里底群岛和哥特兰岛的侏儒鼩鼱异域分布种群与瑞典大陆的同域分布种群来检验这一预测。异域分布时的种群密度高于同域分布。在外赫布里底群岛发现了生态位理论所预测的异域分布时较低的总密度，但在哥特兰岛没有发现。作为重要食物来源的步甲的大小分布并不能解释种群密度的差异。由于所有区域都有鸟类捕食者和蛇类，因此得出结论，秋季侏儒鼩鼱的种群密度主要受同域分布区域内与普通鼩鼱竞争的调节。
