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 (i) a deleterious effect in the first generations when the introduced population was small and (ii) a beneficial impact brought about by metapopulation effects in the subsequent generations. Interestingly, populations displayed a pushed invasion pattern promoting early establishment, which was mainly underpinned by dispersal stochasticity an 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子，是入侵生物学领域的重大研究难题。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 effects）而走向灭绝。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机制仍有待进一步阐明。为更深入地厘清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中的种群动态随机模型，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中开展昆虫寄生蜂（Trichogramma chilonis）的人工引种实验，对模型所得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影响：(i) 当外来种群规模较小时，连通性在初代会产生有害效应；(ii) 而在后续世代中，集合种群效应（metapopulation effects）会带来积极影响。值得注意的是，种群呈现出推动型入侵模式，可促进早期定殖，这一现象主要由扩散随机性与景观的离散性所驱动。本研究结果阐明了景观连通性对种群定殖动态的关键调控作用。