Unnsteinsdottir E R, Hersteinsson P, Pálsson S, Angerbjörn A
The Icelandic Institute of Natural History, Urridaholtsstraeti 6-8, P.O. Box 125, 212, Gardabaer, Iceland.
Institute of Biology, University of Iceland, Sturlugata 7, 101, Reykjavik, Iceland.
Oecologia. 2016 Aug;181(4):1129-38. doi: 10.1007/s00442-016-3635-0. Epub 2016 Apr 28.
In territorial species, observed density dependence is often manifest in lowered reproductive output at high population density where individuals have fewer resources or are forced to inhabit low-quality territories. The Arctic fox (Vulpes lagopus) in Iceland is territorial throughout the year and feeds mostly on birds, since lemmings are absent from the country. Thus, the population does not exhibit short-term population cycles that are evident in most of the species' geographical range. The population has, however, gone through a major long-term fluctuation in population size. Because of the stability in hunting effort and reliable hunting records since 1958, the total number of adult foxes killed annually can be used as an index of population size (N t ). An index of carrying capacity (K) from population growth data for five separate time blocks during 1958-2007 revealed considerable variation in K and allowed a novel definition of population density in terms of K, or N t /K. Correlation analysis suggested that the reproductive rate was largely determined by the proportion of territorial foxes in the population. Variation in litter size and cub mortality was, on the other hand, related to climatic variation. Thus, Arctic foxes in Iceland engage in typical contest competition but can adapt their territory sizes in response to both temporal and spatial variation in carrying capacity, resulting in surprisingly little variation in litter size.
在领地性物种中，观察到的密度依赖性通常表现为在高种群密度下繁殖产出降低，此时个体拥有的资源较少，或者被迫栖息在低质量的领地。冰岛的北极狐（Vulpes lagopus）全年都具有领地性，主要以鸟类为食，因为该国没有旅鼠。因此，该种群没有表现出在该物种大部分地理分布范围内明显的短期种群周期。然而，该种群在种群数量上经历了一次重大的长期波动。由于自1958年以来狩猎努力的稳定性和可靠的狩猎记录，每年捕杀的成年狐狸总数可作为种群数量（N t ）的指标。根据1958 - 2007年期间五个不同时间段的种群增长数据得出的承载能力（K）指标显示，K值存在相当大的变化，并允许根据K值或N t /K对种群密度进行新的定义。相关分析表明，繁殖率在很大程度上由种群中具有领地的狐狸比例决定。另一方面，窝仔数和幼崽死亡率的变化与气候变化有关。因此，冰岛的北极狐参与典型的竞争竞争，但可以根据承载能力的时间和空间变化调整其领地大小，从而导致窝仔数的变化惊人地小。
