Mundt Christopher C, Sackett Kathryn E
Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331-2902 USA.
Ecosphere. 2012 Mar 9;3(3):art24. doi: 10.1890/ES11-00281.1.
Spatial scale is of great importance to understanding the spread of organisms exhibiting long-distance dispersal (LDD). We tested whether epidemics spread in direct proportion to the size of the host population and size of the initial disease focus. This was done through analysis of a previous study of the effects of landscape heterogeneity variables on the spread of accelerating epidemics of wheat () stripe rust, caused by the fungus f. sp. . End-of-season disease gradients were constructed by estimating disease prevalence at regular distances from artificially inoculated foci of different sizes, in field plots of different dimensions. In one set of comparisons, all linear dimensions (plot width and length, focus width and length, and distance between observation points) differed by a factor of four. Disease spread was substantially greater in large plot/large focus treatments than in small plot/small focus treatments. However, when disease gradients were plotted using focus width as the unit distance, they were found to be highly similar, suggesting a proportional relationship between focus or plot size and disease spread. A similar relationship held when comparing same-size plots inoculated with different-sized foci, an indication that focus size is the driver of this proportionality. Our results suggest that power law dispersal of LDD organisms results in scale-invariant relationships, which are useful for better understanding spatial spread of biological invasions, extrapolating results from small-scale experiments to invasions spreading over larger scales, and predicting speed and pattern of spread as an invasion expands.
空间尺度对于理解具有长距离扩散（LDD）的生物的传播至关重要。我们测试了流行病的传播是否与宿主种群大小和初始病害中心大小成正比。这是通过分析之前一项关于景观异质性变量对由真菌小麦条锈菌引起的小麦条锈病加速流行传播影响的研究来完成的。通过在不同尺寸的田间地块中，从不同大小的人工接种中心开始，以固定距离估计病害流行率，构建季末病害梯度。在一组比较中，所有线性尺寸（地块宽度和长度、中心宽度和长度以及观测点之间的距离）相差四倍。在大地块/大中心处理中，病害传播比小地块/小中心处理中要大得多。然而，当以中心宽度作为单位距离绘制病害梯度时，发现它们非常相似，这表明中心或地块大小与病害传播之间存在比例关系。在比较接种不同大小中心的相同大小地块时，也存在类似的关系，这表明中心大小是这种比例关系的驱动因素。我们的结果表明，LDD生物的幂律扩散导致尺度不变关系，这有助于更好地理解生物入侵的空间传播，将小规模实验结果外推到更大尺度的入侵，并预测随着入侵扩展的传播速度和模式。
