Invasive species are among the major threats to global biodiversity. Plant invasions are often driven by great propagule pressure that overcomes barriers to early colonisation and establishment, such as the biotic resistance from pathogens and seed predators. However, the way in which biotic resistance interacts with propagule pressure and affects seed survival remains poorly understood. Here, we experimentally assessed the effect of seed abundance on seed removal in the Brazilian Cerrado (savanna). We tested whether the invasive Leucaena leucocephala and the native Anadenanthera macrocarpa (both Fabaceae) differ in post‐dispersal seed removal – an indicator of granivore pressure – by different guilds of seed predators, varying seed abundance (2, 5 or 10 seeds of each species per treatment) and distance from a disturbance (5, 20 and 50 m from a firebreak) in two fragments of Cerrado. Treatment encounter, that is the chance of at least one seed being removed, increased 72% from 2 to 10 seeds per treatment, but seed removal increased only by 32%, suggesting a threshold in granivore response to seed availability. Native seeds suffered higher removal than exotic seeds, but removal rates did not vary with distance to disturbance or interact with vertebrate and invertebrate exclusions. Our results suggest a patchy pattern of seed predation influenced by resource abundance and emphasise the efficiency of high propagule pressure in overcoming the density‐dependent biotic resistance during early stages of exotic plant invasions in Cerrado. Seeds of fast‐germinating species, such as L. leucocephala, that reach appropriate spots for regeneration may still overcome the biotic resistance due to the patchy nature of seed predation.

中文翻译：

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种子的丰富度影响巴西大草原中外星人和当地树木的种子去除：对生物抗性的影响

入侵物种是对全球生物多样性的主要威胁。植物的入侵通常是由巨大的繁殖力推动的，克服了早期定居和建立的障碍，例如病原体和种子天敌对生物的抵抗力。然而，生物抗性与繁殖压力相互作用并影响种子存活的方式仍知之甚少。在这里，我们通过实验评估了种子丰富度对巴西Cerrado（savanna）种子去除的影响。我们测试了侵袭性白斑白花病菌和本地大果Anadenanthera macrocarpa（均为豆科）在不同的种子捕食者行会，不同的种子丰度（每种处理方法的每个物种2、5或10个种子）和距干扰的距离（5、20）之间，分散后的种子去除（即食肉压力的指标）有所不同距火警通道50 m）位于塞拉多的两个片段中。每次处理至少有一颗种子被去除的机会增加了72％，从2种种子增加到10颗种子，但去除种子仅增加了32％，这表明食草动物对种子可利用性的反应达到了阈值。本地种子的去除率高于外来种子，但去除率不会因干扰距离而变化，也不会与脊椎动物和无脊椎动物排斥相互作用。我们的结果表明，种子捕食的斑块模式受资源丰富度的影响，并强调了高繁殖体压力在克服Cerrado外来植物入侵的早期阶段对密度依赖性生物抗性方面的效率。快速发芽物种的种子，例如由于种子捕食的斑驳性，到达适当的再生点的白头粉刺仍可克服生物抗性。