Sulkava Risto T, Sulkava Pekka O, Sulkava Pertti E
Department of Biology, University of Joensuu, Joensuu, Finland.
Oecologia. 2007 Sep;153(3):579-88. doi: 10.1007/s00442-007-0774-3. Epub 2007 Jun 14.
Long-term studies were carried out in central Finland between 1985 and 2003 to examine the temporal and spatial variation in the density of otter populations. Snow tracking was used to estimate the total population and the number of litters in the study area. In total 52 otters, including 16 cubs in 11 litters, lived in the study area (1,650 km(2)) in 2002-2003. The otter population clearly increased during the study period. The increase in density of the otter population was sigmoid, indicating that the population had reached the local carrying capacity. The density of the population was 0.12 individuals per river ha in 1985 and 0.29 individuals per river ha in 2002. The number of cubs per litter decreased when the density of the population increased. Density-dependent offspring production, together with the auto-correlation function of growth rate, indicates intraspecific competition in otter populations. Otters in a few river systems produced most of the cubs, creating several small source populations in the entire study area. Otters in secondary (sink) habitats had a low reproduction rate. Most otters lived in river systems with large lake surfaces. The number or area of lakes within the river system correlated positively with the total number of otters, litters and cubs in the river system. The six river systems (out of 16) with the largest water area of lakes produced 81.2% of all cubs born in the study area. However, the population growth rate per river hectare or per river kilometre was equal in all kinds of river systems. Thus, among local otter populations in central Finland, a source-sink system between different habitats seems to be prevalent.
1985年至2003年期间，在芬兰中部开展了长期研究，以调查水獭种群密度的时空变化。通过雪地追踪来估计研究区域内的水獭总数和产仔窝数。2002年至2003年期间，共有52只水獭生活在研究区域（1650平方公里），其中包括11窝中的16只幼崽。在研究期间，水獭种群数量明显增加。水獭种群密度的增加呈S形，表明该种群已达到当地的承载能力。1985年种群密度为每公顷河流0.12只，2002年为每公顷河流0.29只。随着种群密度的增加，每窝幼崽的数量减少。密度依赖的后代繁殖，以及增长率的自相关函数，表明水獭种群存在种内竞争。少数河流系统中的水獭产下了大部分幼崽，在整个研究区域形成了几个小的源种群。次生（汇）栖息地的水獭繁殖率较低。大多数水獭生活在湖面较大的河流系统中。河流系统内湖泊的数量或面积与该河流系统中水獭、产仔窝数和幼崽的总数呈正相关。湖泊水域面积最大的16个河流系统中的6个，产下了研究区域内所有幼崽的81.2%。然而，各类河流系统中每公顷河流或每公里河流的种群增长率是相等的。因此，在芬兰中部的当地水獭种群中，不同栖息地之间的源-汇系统似乎很普遍。
