Data from: The highs and lows of dispersal: how connectivity and initial population size jointly shape establishment dynamics in discrete landscapes

Identifying the main factors driving introduced populations to establishment is a major challenge of invasion biology. Due to their small initial size, introduced populations are most vulnerable to extinction because of demographic stochasticity or Allee effects. While an increase in initial population size is known to increase establishment success, much remains to be understood regarding its interplay with connectivity in spatially structured environments. In order to better understand how demographic mechanisms interact at such spatial scale, we developed a stochastic model of population dynamics in discrete space to investigate the effect of connectivity and initial population size on establishment. The predictions derived from the model were then tested using experimental introductions of an insect parasitoid (Trichogramma chilonis) in spatially structured laboratory microcosms. Both theoretical and experimental results demonstrated that the connectivity of the introduction site had 1) a deleterious effect in the first generation when the introduced population was small and 2) a beneficial impact brought about by metapopulation effects in the subsequent generations. Interestingly, populations displayed a weakly pushed invasion pattern promoting early establishment, which was mainly underpinned by dispersal stochasticity and the discrete nature of the landscape. These results shed light on the critical influence of landscape connectivity on establishment dynamics.

探明驱动外来种群成功定殖的核心影响因素，是入侵生物学（invasion biology）领域的核心研究挑战之一。由于初始种群规模较小，外来种群极易因种群统计随机性（demographic stochasticity）或阿利效应（Allee effect）而濒临灭绝。尽管已有研究证实提升初始种群规模可提高定殖成功率，但在空间结构化环境中，其与连通性（connectivity）之间的相互作用机制仍有诸多待解之处。为更深入地解析种群统计机制在该空间尺度下的相互作用模式，我们构建了离散空间种群动态的随机模型，以探究连通性与初始种群规模对种群定殖的影响。随后，我们通过在空间结构化实验室微宇宙（laboratory microcosms）中开展昆虫寄生蜂（Trichogramma chilonis，螟黄赤眼蜂）的人工引种实验，对模型推导得到的预测结果进行了验证。理论与实验结果均表明，引种位点的连通性会产生两类效应：其一，当外来种群规模较小时，会在初代产生有害影响；其二，在后续世代中，会因集合种群（metapopulation）效应带来有益作用。值得关注的是，种群呈现出一种可促进早期定殖的弱推进型入侵格局，该格局主要由扩散随机性（dispersal stochasticity）与景观的离散性所驱动。本研究结果阐明了景观连通性（landscape connectivity）对种群定殖动态的关键影响。