Casini Michele, Rouyer Tristan, Bartolino Valerio, Larson Niklas, Grygiel Włodzimierz
Swedish University of Agricultural Sciences, Department of Aquatic Resources, Institute of Marine Research, Lysekil, Sweden.
University of Oslo, Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, Oslo, Norway; UMR 212 EME, IFREMER (Institut Français de Recherche pour l'Exploitation de la mer), Sète, France.
PLoS One. 2014 Apr 3;9(4):e92278. doi: 10.1371/journal.pone.0092278. eCollection 2014.
Spatio-temporal density-dependent processes are crucial regulatory factors for natural populations. However, there is a lack of studies addressing spatial density-dependence in fish growth. A previous investigation has suggested spatio-temporal density-dependence in body condition of Baltic sprat. Here, we used different techniques, such as centre of gravity, distance, and homogeneity indices, to better characterize the spatial and temporal variations in sprat density and body condition in the Baltic Proper. Our results evidenced a negative spatio-temporal co-variation between the centres of gravity of density and maximum condition. In the 1980s-early 1990s both centres were located in the middle of the Baltic Proper. From the mid 1990s the centres progressively separated in space, as the sprat population moved towards the north-eastern Baltic Proper, and the centre of maximum condition towards the south-western areas. Moreover, at low abundances, sprat density and condition were homogeneously distributed in space, whereas at high abundances both density and condition showed pronounced geographical gradients. The ecological processes potentially explaining the observed patterns were discussed in the light of the Ideal Free Distribution theory. We provide evidence that the shift in the spatial distribution of cod, the main predator of sprat, has been the main factor triggering the overall spatial changes in sprat density, and thus condition, during the past thirty years. The spatial indices shown here, synthesizing the spatio-temporal patterns of fish distribution, can support the implementation of the EU Marine Strategy Framework Directive.
时空密度依赖过程是自然种群的关键调节因素。然而，目前缺乏关于鱼类生长中空间密度依赖性的研究。此前的一项调查表明波罗的海黍鲱的身体状况存在时空密度依赖性。在此，我们使用了不同的技术，如重心、距离和均匀度指数，以更好地描述波罗的海中部黍鲱密度和身体状况的时空变化。我们的结果证明了密度重心与最大身体状况之间存在负时空协变关系。在20世纪80年代至90年代初，两个重心都位于波罗的海中部。从20世纪90年代中期开始，随着黍鲱种群向波罗的海东北部移动，最大身体状况重心向西南部地区移动，两个重心在空间上逐渐分离。此外，在低丰度时，黍鲱密度和身体状况在空间上均匀分布，而在高丰度时，密度和身体状况都呈现出明显的地理梯度。我们根据理想自由分布理论讨论了可能解释观察到的模式的生态过程。我们提供的证据表明，在过去三十年中，黍鲱的主要捕食者鳕鱼空间分布的变化是引发黍鲱密度以及身体状况整体空间变化的主要因素。这里展示的空间指数综合了鱼类分布的时空模式，可以支持欧盟海洋战略框架指令的实施。
