Data from: Neighbourhood effects on plant reproduction: an experimental-analytical framework and its application to the invasive Senecio inaequidens

1. Density-dependence is of fundamental importance for population and range dynamics. Density-dependent reproduction of plants arises from competitive and facilitative plant-plant interactions that can be pollination-independent or pollination-mediated. In small and sparse populations, conspecific density-dependence often turns from negative to positive and causes Allee effects. Reproduction may also increase with heterospecific density (community-level Allee effect), but the underlying mechanisms are poorly understood and the consequences for community dynamics can be complex. Allee effects have crucial consequences for the conservation of declining species, but also the dynamics of range edge populations. In invasive species, Allee effects may slow or stop range expansion.
2. Observational studies in natural plant communities cannot distinguish whether reproduction is limited by pollination-mediated interactions among plants or by other neighbourhood effects (e.g. competition for abiotic resources). Even experimental pollen supply cannot distinguish whether variation in reproduction is caused by direct density effects or by plant traits correlated with density. Finally, it is unknown over which spatial scales pollination-mediated interactions occur.
3. To circumvent these problems, we introduce a comprehensive experimental and analytical framework which simultaneously (1) manipulates pollen availability and quality by hand pollination and pollinator exclusion, (2) manipulates neighbourhoods by transplanting target plants, and (3) analyses the effects of con- and heterospecific neighbourhoods on reproduction with spatially-explicit trait-based neighbourhood models.
4. Applying this framework to Senecio inaequidens, one of Europe’s fastest plant invaders, we found that the seed set was strongly pollen-limited. Reproduction had increased by pollinator-mediated facilitation by both con- and heterospecific neighbours which may lead to (community-level) Allee effects. Pollination-independent interactions, such as amelioration of abiotic conditions through neighbours, contributed to additional positive neighbour effects. However, these pollination-independent interactions were weaker than the pollination-mediated interactions and they occurred over smaller spatial scales. Finally, the strength and direction of neighbourhood effects depended on neighbour traits and thus changed with the trait composition of the neighbourhood.
5. Synthesis. By manipulating both pollen availability and target plant locations within neighbourhoods, we can comprehensively analyse spatially-explicit density-dependence of plant reproduction. This experimental approach enhances our ability to understand the dynamics of sparse populations and of species’ geographical ranges.

1. 密度依赖对种群动态与分布范围动态具有核心意义。植物的密度依赖繁殖源于植物间的竞争与促进作用，这类作用可分为不依赖传粉的与传粉介导的两类。在小型且稀疏的种群中，种内密度依赖效应通常会由负转正，并引发阿利效应（Allee effects）。繁殖成功率也可能随异种密度升高而增加（群落水平阿利效应），但其背后的机制尚不明确，且对群落动态的影响可能极为复杂。阿利效应对濒危物种的保护至关重要，同时也影响着分布边缘种群的动态。对于入侵物种而言，阿利效应可能会减缓甚至阻断其分布范围的扩张。
2. 在天然植物群落中开展的观测研究无法区分，繁殖受限究竟源于植物间传粉介导的相互作用，还是源于其他邻域效应（例如对非生物资源的竞争）。即便通过实验施加花粉供应，也无法区分繁殖变异是由直接密度效应导致，还是由与密度相关的植物性状所引发。此外，目前仍不清楚传粉介导的相互作用发生在哪些空间尺度上。
3. 为规避上述问题，我们提出一套综合的实验与分析框架，该框架可同时实现三项操作：(1) 通过人工授粉与传粉者排除实验，调控花粉的可获得性与质量；(2) 通过移栽目标植株，操控其邻域环境；(3) 基于性状的空间显式邻域模型，分析种内与种间邻域对植物繁殖的影响。
4. 我们将该框架应用于欧洲扩散最快的入侵植物之一——南美千里光（Senecio inaequidens），研究发现其结籽量严重受限于花粉可获得性。繁殖成功率因传粉者介导的种内与种间邻域促进作用而提升，这可能引发（群落水平）阿利效应。不依赖传粉的相互作用（例如邻体改善非生物环境）也带来了额外的正向邻域效应，但这类不依赖传粉的相互作用强度弱于传粉介导的作用，且发生的空间尺度更小。最终，邻域效应的强度与方向取决于邻体性状，因此会随邻域的性状组成发生改变。
5. 综合分析表明，通过同时调控花粉可获得性与目标植株在邻域中的位置，我们可以全面分析植物繁殖的空间显式密度依赖关系。该实验方法有助于我们更深入理解稀疏种群的动态，以及物种的地理分布范围动态。