Department of Biology, University of Florida, P.O. Box 118525, Gainesville, Florida 32611, USA.
Ecology. 2012 Jul;93(7):1571-80. doi: 10.1890/11-1694.1.
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.
繁殖体压力可以决定入侵植物分布范围扩张的成败。分布范围扩张发生在大的空间尺度上，通常包含多种土地覆盖类型，但景观背景对繁殖体压力的影响在很大程度上仍不清楚。许多研究报告称，入侵植物丰度与人类土地利用之间存在正相关关系；在这些景观中，繁殖体压力的增加可能是造成这种相关性的原因。我们检验了这样一个假设，即食无花果鸟类（在城市生境中更为常见）传播种子的速度增加，会导致在以人类土地利用为主的景观中，入侵的绞杀榕属植物数量增加。我们在跨越美国佛罗里达州南部从城市停车场到原生林的整个人类土地利用范围的样方中，量化了入侵物种（榕属 microcarpa）和一种本地物种（榕属 aurea）的丰度。然后，我们比较了基于距离成年无花果种子源和食无花果鸟类栖息地质量预测幼体无花果丰度的模型，以及缺乏其中一个或两个条件的模型。预测入侵榕属幼体丰度的最佳模型同时包含距离成年和食无花果鸟类栖息地的术语，这表明景观对入侵榕属丰度的影响是由传播种子的鸟类介导的。相比之下，预测本地榕属幼体丰度的最佳模型只包含成年个体的存在/缺失，这表明与正在进行分布范围扩张的入侵物种相比，距离单个成年树木对本地物种的种子限制的影响可能较小。然而，两个物种的模型都包含了成年种子源的显著影响，这意味着幼体丰度受到种子到达的限制。这一结果得到了种子添加实验的证实，该实验表明，本地和入侵的绞杀榕属植物都受到强烈的种子限制。了解景观背景如何影响植物入侵的机制可能会导致更好的管理技术。我们的研究结果表明，在有大量食无花果鸟类栖息地的地方，优先移除成年树木可能是控制榕属 microcarpa 丰度的最有效方法。
