As anthropogenic impacts on the natural world escalate, there is increasing interest in the role of humans in dispersing seeds. But the consequences of this Human-Mediated Dispersal (HMD) on plant spatial dynamics are little studied. In this paper we ask how secondary dispersal by HMD affects the dynamics of a natural plant metapopulation. In addition to dispersal between patches, we suggest within-patch processes can be critical. To address this, we assess how variation in local population dynamics, caused by small-scale disturbances, affects metapopulation size. We created an empirically-based model with stochastic population dynamics and dispersal among patches, which represented a real-world, cliff-top metapopulation of wild cabbage Brassica oleracea. We collected demographic data from multiple populations by tagging plants over eight years. We assessed seed survival, and establishment and survival of seedlings in intact vegetation vs small disturbances. We modelled primary dispersal by wind using field data, and used experimental data on secondary HMD by hikers. We monitored occupancy patterns over a 14-year period in the real metapopulation. Disturbance had large effects on local population growth rates, by increasing seedling establishment and survival. This meant that the modelled metapopulation grew in size only when the area disturbed in each patch was above 35%. In these growing metapopulations, although only 0.2% of seeds underwent HMD, this greatly enhanced metapopulation growth rates. Similarly, HMD allowed more colonisations in declining metapopulations under low disturbance, and this slowed the rate of decline. The real metapopulation showed patterns of varying patch occupancy over the survey years, which were related to habitat quality, but also positively to human activity along the cliffs, hinting at beneficial effects of humans. These findings illustrate that realistic changes to dispersal or demography, specifically by humans, can have fundamental effects on the viability of a species at the landscape scale.

中文翻译：

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人类介导的传播和干扰塑造了长寿药草的元种群动态

随着人类对自然界的影响不断升级，人们对人类在传播种子方面的作用越来越感兴趣。但是很少有人研究这种人为介导的扩散 (HMD) 对植物空间动态的影响。在本文中，我们询问 HMD 的二次扩散如何影响天然植物群落的动态。除了补丁之间的分散之外，我们建议补丁内的过程也很关键。为了解决这个问题，我们评估了由小规模干扰引起的当地种群动态的变化如何影响集合种群的大小。我们创建了一个基于经验的模型，该模型具有随机种群动态和斑块之间的分散，代表了野生卷心菜甘蓝的真实世界的悬崖顶复合种群。我们通过标记植物超过八年从多个种群中收集人口统计数据。我们评估了种子存活率，以及完整植被与小干扰下幼苗的建立和存活。我们使用现场数据模拟了风的初级传播，并使用了徒步旅行者对二级 HMD 的实验数据。我们监测了 14 年间真实集合种群的入住率模式。通过增加幼苗的建立和存活，干扰对当地人口增长率产生了很大影响。这意味着仅当每个补丁中受干扰的区域超过 35% 时，建模的集合种群才会增长。在这些不断增长的群体中，虽然只有 0.2% 的种子经历了 HMD，但这大大提高了群体的增长率。同样，HMD 允许在低干扰下在下降的元群中进行更多的定植，这减缓了下降的速度。真实的复合种群在调查年份中显示出不同的斑块占用模式，这与栖息地质量有关，但也与悬崖沿线的人类活动呈正相关，暗示人类的有益影响。这些发现表明，散布或人口统计学的现实变化，特别是人类的变化，可以对景观尺度上物种的生存能力产生根本性影响。