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因素，是入侵生物学（invasion biology）领域的重大研究挑战。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）而面临灭绝风险。尽管已知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，其与连通性之间的相互作用仍有诸多待解之处。为进一步明晰种群统计机制在该空间尺度下的相互作用模式，本研究构建了离散空间中的种群动态随机模型，以探究连通性与初始种群规模对定殖过程的影响。随后，通过在空间结构化的实验室微宇宙中开展昆虫寄生蜂（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，引种位点的连通性存在双重效应：1）当外来种群规模较小时，会在初代产生有害影响；2）在后续世代中，因集合种群（metapopulation）效应而带来有益作用。值得注意的是，种群呈现出弱促进型入侵模式，可提早定殖进程，这一现象主要由扩散随机性（dispersal stochasticity）与景观的离散性所驱动。本研究结果揭示了景观连通性对种群定殖动态的关键调控作用。