Data from: Limited emigration from an outbreak of a forest pest insect

Population density and individual dispersal behaviour affect species´ distribution dynamics. Population densities vary over time, and some species occasionally increase to very high numbers, for example during outbreaks. In such situations populations are expected to expand into new areas due to density-dependent dispersal and sometimes even result in range expansion. A local population of the northern pine processionary moth Thaumetopoea pinivora has recently reached outbreak densities at the edge of its northern range at the southern tip of Gotland Island in the Baltic Sea. We first investigated if the outbreak had resulted in establishment of populations in suitable habitats on Gotland Island outside of the outbreak area. Six small populations were found that could potentially have originated from the outbreak area. However, data from 12 microsatellite markers strongly suggest that these populations did not originate from the recent outbreak. Genetic variability was not reduced in these small, isolated populations and there were several unique alleles, indicating instead a different population history and that there has been no recent range expansion. In addition, there was apparent genetic isolation by geographic distance, implying that despite that the outbreak population reached a high enough density to cause density-dependent dispersal, significant gene flow has not occurred.种群密度与个体扩散行为共同影响物种的分布动态。种群密度随时间动态波动，部分物种会在种群暴发（outbreak）期达到极高的种群数量。在此类情形下，种群会因密度依赖型扩散（density-dependent dispersal）向新区域扩张，有时甚至会引发分布范围拓展（range expansion）。近期，栖息于波罗的海哥特兰岛南端其北部分布范围边缘的一处北方松异舟蛾（Thaumetopoea pinivora）局域种群已达到种群暴发密度。本研究首先探究此次种群暴发是否促使该种群在暴发区域外的哥特兰岛适宜生境中建立新种群。研究共发现6个小型种群，理论上可能源自该暴发种群。然而，基于12个微卫星标记（microsatellite markers）的遗传数据分析强烈表明，这些小型种群并非起源于此次近期暴发。这些小型孤立种群的遗传变异水平并未出现下降，且存在多个特有等位基因（unique alleles），这反而说明它们拥有独立的种群历史，且近期并未发生分布范围拓展。此外，研究观察到显著的地理距离介导的遗传隔离现象，这意味着尽管该暴发种群已达到足以引发密度依赖型扩散的种群密度，但并未发生显著的基因流（gene flow）。