Støen Ole-Gunnar, Zedrosser Andreas, Saebø Solve, Swenson Jon E
Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O.Box 5003, 1432, As, Norway.
Oecologia. 2006 Jun;148(2):356-64. doi: 10.1007/s00442-006-0384-5. Epub 2006 Feb 18.
There is considerable controversy in the literature about the presence of density dependence in dispersal. In this study, we exploit a data series from a long-term study (>18 years) on radio-marked brown bears (Ursus arctos L.) in two study areas in Scandinavia to investigate how individual-based densities influence the probability of natal dispersal and natal dispersal distances. Cumulatively, 32% and 46% of the females and 81% and 92% of the males dispersed before reaching 5 years of age in the northern and southern study area, respectively. Density had a negative effect on both the probability of dispersal and dispersal distances for the dispersing animals, when controlling for study area, sex and age, making this the first study to show that natal dispersal probability and distances are inversely density dependent in a large carnivore. We suggest that female-female competition for space caused females in higher density areas to settle closer to their natal area. For males, however, merging of demes, resulting in decreased relatedness and increased heterozygosity in an expanding population, might be the reason for shorter dispersal distances in males living at higher densities. This has been hypothesised for small mammals. The high proportion of dispersing female brown bears in Scandinavian compared with North American studies might be due to lower densities in Scandinavia and recent population expansion, with unoccupied areas available at the edges of the population. The longer dispersal distances in female Scandinavian brown bears suggest less social constraints on movements than for North American females. The longer dispersal distances by Scandinavian males may be due to increased searching for potential mates in peripheral areas with lower densities of females. These results, in addition to results of other brown bear studies, suggest that brown bears might be more territorial than previously thought, and that density is regulated by social interactions.
关于扩散过程中是否存在密度依赖性，文献中存在相当大的争议。在本研究中，我们利用了来自斯堪的纳维亚两个研究区域对无线电标记棕熊（棕熊 Ursus arctos L.）进行的长期研究（超过18年）的数据系列，以调查基于个体的密度如何影响出生扩散概率和出生扩散距离。累计而言，在北部和南部研究区域，分别有32%和46%的雌性以及81%和92%的雄性在5岁之前扩散。在控制研究区域、性别和年龄后，密度对扩散个体的扩散概率和扩散距离均有负面影响，这使得本研究首次表明，大型食肉动物的出生扩散概率和距离与密度呈负相关。我们认为，雌性之间对空间的竞争导致高密度区域的雌性在更靠近其出生区域的地方定居。然而，对于雄性来说，种群合并导致在扩张种群中亲缘关系降低和杂合度增加，这可能是高密度地区雄性扩散距离较短的原因。对于小型哺乳动物也有过这样的假设。与北美研究相比，斯堪的纳维亚地区扩散的雌性棕熊比例较高，可能是由于斯堪的纳维亚地区密度较低且近期种群扩张，在种群边缘有未被占据的区域。斯堪的纳维亚雌性棕熊较长的扩散距离表明，其行动受到的社会限制比北美雌性棕熊少。斯堪的纳维亚雄性棕熊较长的扩散距离可能是由于在雌性密度较低的周边地区寻找潜在配偶的机会增加。这些结果，以及其他棕熊研究的结果表明，棕熊可能比之前认为的更具领地性，并且密度受社会互动调节。
