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影响入侵植物竞争能力的最常被提及的调控机制之一，但二者对植物种群动态的协同效应在野外实地条件下极少被评估。在评估经典杂草生物防治因子的防控效果时，明确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，可能会对植食者影响的推论产生偏倚。
2. 本研究报道了一项公民科学监测项目的研究成果，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。我们采用种群动态离散模型，对美国爱达荷州38个空间重复样地中宽叶柳穿鱼分株密度（ramet density）变化的内源与外源调控过程的相对重要性进行了量化评估。
3. 基于分株密度的种群人均增长率（per capita population growth rates）分析结果显示，研究样地存在直接密度制约效应，其最可能的成因是种内竞争（intraspecific competition）。分株密度的变化不受本地植物群落（resident plant community）丰度的影响。
4. 在控制密度制约效应的影响后，降水对宽叶柳穿鱼的分株密度具有显著的正向调控作用，而Mecinus janthiniformis的丰度则呈现较弱但显著的负向调控效应。未发现降水与植食作用（herbivory）之间存在交互效应的相关证据。
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特异性差异，生物防治的防控效果在局部入侵斑块中可能存在显著差异。我们建议入侵植物管理策略应将降水监测与生物防治因子监测纳入项目体系，以预估预期的生物防治防控效果。在预计植食者防控效果较弱的区域，应优先采用替代防治手段。