Data from: Urbanized landscapes favored by fig-eating birds increase invasive but not native juvenile strangler fig abundance

Propagule pressure can determine the success or failure of invasive plant range expansion. Range expansion takes place at large spatial scales, often encompassing many types of land cover, yet the effect of landscape context on propagule pressure remains largely unknown. Many studies have reported a positive correlation between invasive plant abundance and human land use; increased propagule pressure in these landscapes may be responsible for this correlation. We tested the hypothesis that increased rates of seed dispersal by fig-eating birds, which are more common in urban habitats, result in an increase in invasive strangler fig abundance in landscapes dominated by human land use. We quantified abundance of an invasive species (Ficus microcarpa) and a native species (F. aurea) of strangler fig in plots spanning the entire range of human land use in South Florida, USA, from urban parking lots to native forest. We then compared models that predicted juvenile fig abundance based on distance to adult fig seed sources and fig-eating bird habitat quality with models that lacked one or both of these terms. The best model for juvenile invasive fig abundance included both distance to adult and fig-eating bird habitat terms, suggesting that landscape effects on invasive fig abundance are mediated by seed-dispersing birds. In contrast, the best model for juvenile native fig abundance included only presence/absence of adults, suggesting that distance from individual adult trees may have less effect on seed limitation for a native species compared to an invasive species undergoing range expansion. However, models for both species included significant effects of adult seed sources, implying that juvenile abundance is limited by seed arrival. This result was corroborated by a seed addition experiment that indicated that both native and invasive strangler figs were strongly seed limited. Understanding how landscape context affects the mechanisms of plant invasion may lead to better management techniques. Our results suggest that prioritizing removal of adult trees in sites with high fig-eating bird habitat may be the most effective method to control F. microcarpa abundance.繁殖体压力（Propagule pressure）可决定入侵植物范围扩张的成败。范围扩张往往发生在大空间尺度上，通常涵盖多种土地覆盖类型，但景观背景对繁殖体压力的影响在很大程度上仍未明确。诸多研究均报道了入侵植物多度与人类土地利用之间的正相关关系；这类生境中升高的繁殖体压力可能正是该相关性的成因。我们检验了如下假说：城市生境中更为常见的食榕鸟类所介导的种子扩散速率提升，会导致人类土地利用主导的景观中入侵绞榕（strangler fig）的多度增加。我们在美国南佛罗里达州覆盖人类土地利用全梯度的样地中（样地范围从城市停车场至原生森林），量化了入侵绞榕物种细叶榕（Ficus microcarpa）与本土绞榕物种F. aurea的多度。随后我们比较了两类预测模型：一类基于距成年绞榕植株种子源的距离与食榕鸟类生境质量，预测榕属幼苗的多度；另一类则缺失其中一项或两项变量。入侵绞榕幼苗多度的最优模型同时纳入了距成年植株距离与食榕鸟类生境两项因子，这表明景观对入侵绞榕多度的影响由种子扩散鸟类所介导。与之相对，本土绞榕幼苗多度的最优模型仅包含成年植株的存在/缺失变量，这意味着相较于正经历范围扩张的入侵物种，本土物种的种子限制受单株成年树木距离的影响更小。不过，两个物种的模型均显示成年种子源具有显著效应，这表明幼苗多度受种子到达量的限制。该结果得到了种子添加实验的佐证，实验表明本土与入侵绞榕均受到强烈的种子限制。明晰景观背景如何调控植物入侵的作用机制，有望助力开发更高效的治理技术。我们的研究结果提示，在食榕鸟类生境质量较高的区域优先移除成年植株，或是控制细叶榕（Ficus microcarpa）多度的最有效手段。