Biological invasions are one of the main threats to biodiversity and ecosystem functioning in the Anthropocene. Fleshy-fruited invasive plants establish mutualistic interactions with native seed dispersers and may affect the mutualisms between native partners, negatively by disrupting plant dispersal through competition for seed dispersers or positively by facilitating seed dispersal via the attraction of fruit-eating animals. Moreover, the invaders' density in the neighborhood of native plants may modulate the direction and/or magnitude of such effects on natives. In mountains of central Argentina, the cessation of fruiting of the dominant native tree Lithraea molleoides overlaps with the beginning of the fruiting of invasive shrubs (Pyracantha spp.). This partial overlap allows for testing opposite predictions regarding the effect of invasive fruits on native seed dispersal. We compared frugivory by seed disperser birds on L. molleoides during non-overlapping and overlapping periods, at six sites that differed in Pyracantha shrub density (high, low and no-invasion). We counted frugivory during 2 h on 15 individuals of L. molleoides at each site and period, totaling 360 h of observation. Frugivory on the native tree was similar among sites during the non-overlapping period and remained constant in both periods at non-invaded sites. At invaded sites, frugivory increased from non-overlapping to overlapping period and was greater at highly invaded sites. The resource provided by Pyracantha did not disrupt seed dispersal of the dominant native tree. Rather, it facilitated frugivory by seed dispersers and this effect may be exacerbated with higher fruit availability of invasives. Our results provide a counterview to the prevailingly negative impacts of invasive species on the seed dispersal of native species since the fruiting of invasive plants facilitated the seed dispersal of native species in a continental region contrasts with the mutualism disruption commonly observed in insular environments.

中文翻译：

---

肉质的入侵灌木间接增加了本地树种的传播

生物入侵是人类世生物多样性和生态系统功能的主要威胁之一。肉质入侵植物与本地种子传播者建立共生相互作用，并可能影响本地伙伴之间的共生关系，消极地通过竞争种子传播者来破坏植物传播，或积极地通过吸引食果动物来促进种子传播。此外，入侵者在本地植物附近的密度可能会调节这种对本地人的影响的方向和/或幅度。在阿根廷中部的山区，占优势的本地树Lithraea molleoides的停止结果与入侵灌木（火棘）的结果开始重叠种）。这种部分重叠允许测试关于入侵水果对本地种子传播的影响的相反预测。我们比较了在不重叠和重叠期间，在火棘灌木密度（高、低和无入侵）不同的六个地点，种子分散鸟在L. molleoides上的食果性。我们在每个地点和时期对 15 个L. molleoides个体在 2 小时内计算了食果性，总共观察了 360 小时。在非重叠期间，本地树上的食果在不同地点之间是相似的，并且在非入侵地点的两个时期都保持不变。在入侵地点，食果性从非重叠期增加到重叠期，并且在高度入侵的地点更大。提供的资源火棘没有扰乱主要本土树种的种子传播。相反，它通过种子分散器促进了食果性，并且这种影响可能会随着入侵物的更高果实可用性而加剧。我们的研究结果为入侵物种对本地物种种子传播的普遍负面影响提供了反驳，因为入侵植物的结果促进了大陆地区本地物种的种子传播，这与在岛屿环境中常见的共生破坏形成对比。