Relatively little experimental evidence is available regarding how ecological resistance and propagule density interact in their effects on the establishment of invasive exotic species. We examined the independent and interactive effects of neighbour cover (biotic resistance), winter vs. spring water addition (abiotic resistance) and seed density on the invasion of the European perennial grass Holcus lanatus into a California coastal grassland dominated by exotic annual grasses. We found that decreased competition from resident exotic grasses had no effect. In contrast, increased late-season water availability eroded the abiotic resistance offered by naturally dry conditions, facilitating invasion. Finally, watering treatment and seed density interacted strongly in determining seedling survival: while seedling mortality was close to 100% in ambient and winter water addition plots, survivor numbers increased with seed density in spring-watered plots. Thus, decreased abiotic resistance can amplify the effect of increased propagule density on seedling establishment, thereby increasing the likelihood of invasion.

译文

:相对而言,关于生态抗性和繁殖密度如何影响外来入侵物种建立的相互作用的实验证据很少。我们研究了邻居覆盖物(生物抗性),冬季水与泉水的添加量(非生物抗性)以及种子密度对欧洲多年生禾草Holcus lanatus进入以异国一年生禾本科草为主的加利福尼亚沿海草原的入侵的独立和交互作用。我们发现,来自本地奇异草的竞争减少没有影响。相反,增加的后期可用水侵蚀了自然干燥条件下产生的非生物抗性,从而促进了入侵。最后,浇水处理和种子密度在决定幼苗存活方面有很强的相互影响:在环境和冬季水源地中,幼苗死亡率接近100%,而春季灌溉地中,存活人数随着种子密度的增加而增加。因此,降低的非生物抗性可以放大繁殖体密度增加对幼苗建立的影响,从而增加入侵的可能性。

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