Skorping Arne
Institute of Biology and Geology, Department of Ecology, University of Tromsø, Guleng, P.O. Box 3085, N-9001, Tromsø, Norway.
Oecologia. 1984 Sep;64(1):34-40. doi: 10.1007/BF00377540.
Density-dependent effects in Elaphostrongylus rangiferi, a parasitic nematode in the CNS and muscular system of reindeer, were studied in a laboratory population of the snail intermediate host, Arianta arbustorum. The rates in parasite growth, development and mortality were all affected by parasite density. The effects on growth and development were, however, much more marked, than the effect on mortality.All density-dependent rates were intensified by decreasing snail size, and by snail starvation. The snail host showed marked tissue reactions against infection, and the intensity of these reactions increased with increasing parasite density. The mechanism behind the observed density-dependent rates is discussed, and is tentatively concluded to be competition for nutritive substances in the host tissue.The importance of a density-dependent developmental rate in natural populations of this parasite is discussed, and it is hypothesized that this effect may counteract the strong temperature-dependent developmental rate of E. rangiferi In a more general context it is pointed out that density-dependent developmental rates, although common amongst animal populations, has been neglected in models of population dynamics. Developmental rates are usually represented by a constant time lag in such models, but should be treated as a density-dependent variable.
在实验室条件下，以中间宿主蜗牛（Arianta arbustorum）为研究对象，对寄生于驯鹿中枢神经系统和肌肉系统的寄生线虫——驯鹿后圆线虫（Elaphostrongylus rangiferi）的密度依赖效应进行了研究。寄生虫的生长、发育和死亡率均受寄生虫密度的影响。然而，密度对生长和发育的影响比对死亡率的影响更为显著。所有密度依赖率都因蜗牛体型减小和饥饿而增强。蜗牛宿主对感染表现出明显的组织反应，且这些反应的强度随寄生虫密度的增加而增强。文中讨论了观察到的密度依赖率背后的机制，并初步得出结论，其机制为宿主组织中营养物质的竞争。文中还讨论了这种寄生虫自然种群中密度依赖发育率的重要性，并推测这种效应可能会抵消驯鹿后圆线虫强烈的温度依赖发育率。在更广泛的背景下指出，密度依赖发育率虽然在动物种群中很常见，但在种群动态模型中却被忽视了。在这类模型中，发育率通常用一个固定的时间滞后表示，但应将其视为一个密度依赖变量。
