Rouget Mathieu, Richardson David M
Institute for Plant Conservation, Botany Department, University of Cape Town, Rondebosch 7701, South Africa.
Am Nat. 2003 Dec;162(6):713-24. doi: 10.1086/379204. Epub 2003 Oct 22.
Propagule pressure is intuitively a key factor in biological invasions: increased availability of propagules increases the chances of establishment, persistence, naturalization, and invasion. The role of propagule pressure relative to disturbance and various environmental factors is, however, difficult to quantify. We explored the relative importance of factors driving invasions using detailed data on the distribution and percentage cover of alien tree species on South Africa's Agulhas Plain (2,160 km2). Classification trees based on geology, climate, land use, and topography adequately explained distribution but not abundance (canopy cover) of three widespread invasive species (Acacia cyclops, Acacia saligna, and Pinus pinaster). A semimechanistic model was then developed to quantify the roles of propagule pressure and environmental heterogeneity in structuring invasion patterns. The intensity of propagule pressure (approximated by the distance from putative invasion foci) was a much better predictor of canopy cover than any environmental factor that was considered. The influence of environmental factors was then assessed on the residuals of the first model to determine how propagule pressure interacts with environmental factors. The mediating effect of environmental factors was species specific. Models combining propagule pressure and environmental factors successfully predicted more than 70% of the variation in canopy cover for each species.
繁殖体可获得性的增加会提高定殖、存续、归化和入侵的几率。然而，繁殖体压力相对于干扰和各种环境因素的作用难以量化。我们利用南非厄加勒斯平原（2160平方公里）外来树种分布和盖度百分比的详细数据，探究了驱动入侵的因素的相对重要性。基于地质、气候、土地利用和地形的分类树能够充分解释三种广泛分布的入侵物种（独眼金合欢、银荆和海岸松）的分布，但无法解释其丰度（树冠盖度）。随后，我们开发了一个半机理模型，以量化繁殖体压力和环境异质性在构建入侵模式中的作用。繁殖体压力强度（通过与假定入侵源的距离近似）比任何考虑到的环境因素都更能预测树冠盖度。然后，我们在第一个模型的残差上评估环境因素的影响，以确定繁殖体压力如何与环境因素相互作用。环境因素的中介作用具有物种特异性。结合繁殖体压力和环境因素的模型成功预测了每个物种树冠盖度变化的70%以上。
