Hertzberg K, Yoccoz N G, Ims R A, Leinaas H P
Eastern Norway Research Institute, P.O. Box 1066, Skurva, 2601 Lillehammer, Norway, , , , , , NO.
Norwegian Institute for Nature Research (NINA), Polar Environmental Centre, 9296 Tromsø, Norway e-mail:
Oecologia. 2000 Aug;124(3):381-390. doi: 10.1007/s004420000398.
The population density and demography of five species of arctic Collembola were studied in a naturally patchy habitat, consisting of Carex ursinae tussocks with varying degrees of isolation. Focal predictor variables were those describing the spatial configuration of tussocks, including tussock size and isolation and the amount of habitat (cover) at a 1-m scale surrounding each tussock population. The Collembola populations were heavily influenced by environmental stochasticity in the form of winter mortality and summer drought, and the influence of patchiness on population characteristics was evaluated in this context. The five species showed very different responses to the structuring effect of the habitat, depending on life history characteristics, mobility and habitat requirements. Population density was highly variable in both time and space. Spring densities indicated larger winter mortality compared to observations from a previous study, and the snow- and ice-free season from June to August only resulted in population growth for Folsomia sexoculata. In the other species, adult mortality must have been high as there was no net population growth despite observed reproduction. The exception was Hypogastrura viatica, whose population decline was more likely to have been the result of migration out of the study area. Cover was the most important variable explaining density. No pure area or isolation effects at the tussock level were detected, even in areas with very low habitat cover. Drought was probably an important mortality factor, as July was particularly warm and dry. Due to qualitative differences in the tussocks and the matrix substrate, desiccation risk would be higher during dispersal between tussocks. We suggest that increased dispersal mortality gave the observed pattern of increased density in relation to cover, both in general and in F. quadrioculata, an opportunistic species otherwise known for rapid population growth. Onychiurus groenlandicus, which had a similar density response to cover, may also be influenced by a rescue effect sustaining densities in areas with high cover. The cover effect can be viewed as a large-scale factor which encompasses the general spatial neighbourhood of each tussock, where inter-population processes are important, as opposed to internal patch dynamics.
在一个自然形成的斑块状栖息地中，对五种北极弹尾虫的种群密度和种群统计学特征进行了研究，该栖息地由不同程度隔离的熊苔草草丛组成。重点预测变量是描述草丛空间配置的变量，包括草丛大小、隔离程度以及每个草丛种群周围1米范围内的栖息地（覆盖物）数量。弹尾虫种群受到冬季死亡率和夏季干旱等形式的环境随机性的严重影响，并在此背景下评估了斑块性对种群特征的影响。这五个物种对栖息地的结构效应表现出非常不同的反应，这取决于它们的生活史特征、移动性和栖息地需求。种群密度在时间和空间上都高度可变。与之前一项研究的观察结果相比，春季密度表明冬季死亡率更高，而6月至8月的无雪无冰季节仅导致六眼弗氏跳虫的种群增长。在其他物种中，尽管观察到有繁殖现象，但由于没有净种群增长，成年个体的死亡率一定很高。例外的是维亚蒂卡矮跳虫，其种群数量下降更可能是迁移出研究区域的结果。覆盖物是解释密度的最重要变量。即使在栖息地覆盖度非常低的区域，也未检测到草丛水平上的纯粹面积或隔离效应。干旱可能是一个重要的死亡因素，因为7月特别温暖干燥。由于草丛和基质底物在质量上存在差异，在草丛之间扩散时脱水风险会更高。我们认为，扩散死亡率的增加导致了观察到的与覆盖度相关的密度增加模式，总体而言以及在四眼弗氏跳虫中都是如此，四眼弗氏跳虫是一种以种群快速增长而闻名的机会主义物种。格陵兰长角跳虫对覆盖度有类似的密度反应，它也可能受到一种救援效应的影响，这种效应维持了高覆盖度区域的种群密度。覆盖效应可以被视为一个大规模因素，它涵盖了每个草丛的一般空间邻域，在这个邻域中，种群间过程很重要，这与内部斑块动态形成对比。
