Data from: Density dependence, precipitation, and biological control agent herbivory influence landscape-scale dynamics of the invasive Eurasian plant Linaria dalmatica

1. Resource availability and natural enemies are among the most commonly cited mechanisms affecting competitive ability of invasive plants, but their simultaneous effects on plant dynamics are seldom evaluated in the field. Understanding how endogenous and exogenous factors affect invasive plant abundance is essential when evaluating the impact of classical weed biological control agents because misinterpretations of the mechanisms regulating plant demography may bias inference of herbivore impact. 2. In this study we report results from a citizen-science monitoring program initiated to evaluate the effects of the stem–mining weevil Mecinus janthiniformis on the Eurasian invasive weed Dalmatian toadflax Linaria dalmatica. We used a discrete model of population dynamics to evaluate the relative importance of endogenous and exogenous processes affecting changes in ramet density of L. dalmatica at 38 spatially replicated sites in Idaho, USA. 3. Analysis of per capita population growth rates based on ramet density indicated the presence of direct density dependence, which was most likely due to intraspecific competition. Changes in ramet density were not influenced by the abundance of the resident plant community. 4. Precipitation had a strong, positive effect on ramet density of L. dalmatica while the abundance of M. janthiniformis had a weaker, but significant, negative effect after accounting for the density dependence. There was no support for an interactive effect between precipitation and herbivory. 5. Synthesis and applications. Our results indicate that biological control is an important factor affecting weed population growth at the landscape scale, but they also suggest that biological control impact may vary considerably on local infestations due to site-specific variation in rainfall and density-dependent processes. We recommend that invasive plant management strategies integrate precipitation and biological control agent monitoring into their programs to estimate expected biological control efficacy. Alternative control methods should be prioritized in areas where herbivore impact is expected to be low.1. 资源可获得性与天敌是学界最常提及的影响入侵植物竞争能力的机制之一，但二者对植物种群动态的协同效应在野外研究中却极少被评估。在评估经典杂草生物防治因子的防控效果时，明晰内源与外源因子如何调控入侵植物的种群丰度至关重要——因为对植物种群动态调控机制的误判，可能会导致植食者影响的推断出现偏倚。2. 本研究报告了一项公民科学监测项目的成果，该项目旨在评估蛀茎象甲（stem-mining weevil）Mecinus janthiniformis对欧亚入侵杂草宽叶柳穿鱼（Dalmatian toadflax）Linaria dalmatica的防控效应。我们采用种群离散动态模型，针对美国爱达荷州38个空间重复样地中的宽叶柳穿鱼分株密度（ramet density）变化，解析调控其种群动态的内源与外源过程的相对重要性。3. 基于分株密度的种群个体增长率（per capita population growth rates）分析结果显示，研究样地存在直接密度制约（density dependence）效应，其最可能的成因是种内竞争（intraspecific competition）。而本地植物群落的丰度并未对宽叶柳穿鱼的分株密度变化产生显著影响。4. 在控制密度制约效应的前提下，降水对宽叶柳穿鱼的分株密度具有显著正向调控作用，而Mecinus janthiniformis的种群丰度则仅表现出较弱但仍显著的负向效应。本研究未发现降水与植食作用之间存在交互效应的证据。5. 综合与应用。本研究结果表明，生物防治是影响景观尺度（landscape scale）下杂草种群增长的重要因子，但同时也提示，由于不同样地的降水条件与密度制约过程存在差异，生物防治的防控效果在局部入侵斑块中可能存在显著变异。我们建议入侵植物管理方案应将降水与生防因子监测纳入其中，以预估预期的生物防控效能；在预计植食者防控效果较弱的区域，则应优先考虑采用替代防治手段。