Biogeographic variation of distance‐dependent effects in an invasive tree species. (3rd March 2019) - Yang, Qiang
Abstract: Plant pathogens and herbivores can maintain forest diversity by reducing survival of tree seedlings close to conspecifics. However, how biogeographic variation in these natural enemies affects such distance‐dependent processes is unknown. Because invasive plants escape ecologically important enemies when introduced to a new range, distance‐dependent mortality may differ between their native and introduced ranges. Here, we test whether the invasive tree Triadica sebifera escaped distance‐dependent mortality when introduced to the United States from China, and examine the roles of natural enemies in native and introduced ranges. In both the United States and China, we performed field surveys along with field and greenhouse experiments with field‐collected soils and soil sterilization treatments. In field surveys and the field experiment, insect damage on T. sebifera seedlings decreased with distance to conspecific trees in the native range (China), but damage was low at all distances in the introduced range (United States). In the greenhouse experiment testing the effects of soil pathogens, T. sebifera seedling mortality decreased with soil distance from conspecific trees in both ranges but distance‐independent mortality was higher in native range soils. Our findings indicate that both insect herbivores and the soil biota contribute to distance‐dependent effects on T. sebifera in its native range. They suggest, however, that plants may more readily escape herbivore than soil biota distance‐dependent effects when introduced to a new range and so herbivores, rather than soil pathogens, contribute more strongly to biogeographic variation in distance‐dependent effects. These results highlight the importance of considering species biogeographic variation in distance‐dependent effects and teasing apart the roles that different natural enemies play when studying species coexistence, community diversity and biological invasions. Abstract : Plain Language Summary 摘要: 物种共存和生物多样性维持一直是生态学研究的中心论题。负密度制约(也称Janzen‐Connell假说)是影响植物群落物种组成的重要理论之一。有害生物(如：食草动物和病原微生物)对植物体的侵害是导致负密度制约效应发生的主要原因。区别不同类型的有害生物在负密度制约效应中的相对重要性是近年来研究的一个热点和难点问题。入侵性木本植物从一个区域引入到新的区域后，天敌的逃逸是否影响了负密度制约效应的发生。本实验以多年生木木植物乌桕为研究对象，在乌桕的原产地中国和入侵地美国，采用野外调查、野外同质园、室内控制试验的实验手段，研究乌桕从中国入侵到美国后，天敌的逃逸是否使乌桕逃离了负密度制约效应的限制。我们的实验结果表明，在乌桕的原产地，植食性昆虫和土壤病原微生物在负密度制约效应中都起着重要的作用，但是，乌桕从中国引入到美国之后，仅逃离了植食性昆虫所造成的负密度制约效应，但是并没有逃离土壤病原微生物所造成的负密度制约效应。研究结果有助于揭示不同类别的天敌在负密度制约效应中的相对重要性，并对阐明木本植物的入侵机制以及开展合理有效的生物防治措施有重要的意义。 A plain language summary is available for this article.