Data from: Misuse of bird digital distribution maps creates reversed spatial diversity patterns in the Amazon

It is well known that bird richness in the Amazon is greater in upland forests, and that seasonally flooded forest is particularly species-poor. However, the misleading pattern of greater bird richness in seasonally flooded forest has emerged seemingly unnoticed numerous times in richness maps in the literature. We hypothesize that commission errors in digital distribution maps (DDMs) are the cause behind the misleading richness pattern. In the Amazon, commission errors are a consequence of the different methodological treatment given to large-ranged versus small-ranged habitat specialists when mapping distributions. DDMs of 1,007 Amazonian birds were examined, and maps that had commission errors were corrected. We generated two richness maps, one from the overlay of original DDMs and another from the overlay of the corrected ones. We identified 291 species whose distribution maps had errors. In the original data, seasonally flooded forests showed higher species richness than upland forest, but this pattern was reverted in the corrected richness map. Commission errors were 35 times more likely in the seasonally flooded forest. We conclude that DDMs accurately portray the distribution of single species in the Amazon. Commission errors in individual maps, however, accumulate when they are overlaid, explaining the misleading pattern for birds in the Amazon. DDMs can continue to be used mapping richness, as long as, at a regional scale (1) basic map refinements are carried, or (2) only small-range species are used for mapping species richness.

众所周知，亚马逊地区的鸟类物种丰富度在高地森林中更高，而季节性水淹森林的物种丰富度尤其贫乏。然而，在现有文献的物种丰富度地图中，"季节性水淹森林鸟类丰富度更高"这一误导性模式多次出现却未被察觉。我们推测，数字分布地图（digital distribution maps，以下简称DDMs）中的假阳性误差（commission errors）正是这一误导性丰富度模式的成因。在亚马逊地区，假阳性误差源于物种分布制图时，对广幅分布与狭幅分布的生境特化物种采用了不同的方法学处理方式。本研究对1007种亚马逊鸟类的数字分布地图进行了筛查，并修正了存在假阳性误差的地图。我们生成了两张物种丰富度地图：一张基于原始DDMs的叠加，另一张基于修正后的地图叠加。我们共识别出291种存在分布地图误差的鸟类。在原始数据中，季节性水淹森林的物种丰富度高于高地森林，但这一模式在修正后的丰富度地图中被反转。季节性水淹森林中出现假阳性误差的概率是其他区域的35倍。我们的研究结论表明，DDMs能够准确刻画亚马逊地区单物种的分布情况。但单张地图中的假阳性误差在叠加后会产生累积效应，这正是亚马逊地区鸟类丰富度误导性模式的成因。只要在区域尺度上满足以下任一条件，DDMs仍可继续用于物种丰富度制图：（1）完成基础地图优化，或（2）仅以狭幅分布物种为对象开展丰富度制图。