Westerberg Lars, Berglund Hilda-Linn, Jonason Dennis, Milberg Per
IFM Biology, Conservation Ecology Group Linköping University Linköping Sweden.
Ecol Evol. 2021 Mar 15;11(9):3830-3840. doi: 10.1002/ece3.7252. eCollection 2021 May.
When assessing changes in populations of species, it is essential that the methods used to collect data have some level of precision and preferably also good accuracy. One commonly used method to collect pollinators is colour pan traps, but this method has been suggested to be biased by the abundance of surrounding flowers. The present study evaluated the relationship between pan trap catches and the frequency of flowers on small (25 m) and large (2-6 ha) spatial scales. If pan traps work well, one should assume a positive relationship, that is, more insects caught when they have more food. However, in contrast, we found that catches in pan traps were often negatively affected by flower frequency. Among the six taxa evaluated, the negative bias was largest in Vespoidea and Lepturinae, while there was no bias in solitary Apoidea (Cetoniidae, Syrphidae and social Apoidea were intermediate). Furthermore, red flowers seemed to contribute most to the negative bias. There was also a tendency that the negative bias differed within the flight season and that it was higher when considering the large spatial scale compared to the small one. To conclude, pan trap catches may suffer from a negative bias due to surrounding flower frequency and color. The occurrence and magnitude of the negative bias were context and taxon dependent, and therefore difficult to adjust for. Thus, pan traps seem less suited to evaluate differences between sites and the effect of restoration, when gradients in flower density are large. Instead, it seems better suited to monitor population changes within sites, and when gradients are small.
在评估物种种群的变化时，用于收集数据的方法必须具有一定程度的精确性，最好还具有良好的准确性。一种常用的收集传粉者的方法是色盘诱捕法，但有人认为这种方法会受到周围花朵数量的影响而产生偏差。本研究评估了在小空间尺度（25米）和大空间尺度（2 - 6公顷）上色盘诱捕捕获量与花朵频率之间的关系。如果色盘诱捕法效果良好，那么应该存在正相关关系，也就是说，当昆虫有更多食物时会捕获到更多昆虫。然而，与此相反，我们发现色盘诱捕的捕获量常常受到花朵频率的负面影响。在评估的六个分类单元中，胡蜂总科和瘦花天牛亚科的负偏差最大，而独居的蜜蜂总科（花金龟科、食蚜蝇科）没有偏差（熊蜂科和社会性蜜蜂总科处于中间水平）。此外，红色花朵似乎对负偏差的影响最大。在飞行季节内负偏差也存在差异的趋势，并且与小空间尺度相比，在大空间尺度下负偏差更高。总之，色盘诱捕的捕获量可能会因周围花朵的频率和颜色而受到负偏差的影响。负偏差的出现和程度取决于环境和分类单元，因此难以进行调整。因此，当花朵密度梯度较大时，色盘诱捕似乎不太适合评估不同地点之间的差异以及恢复效果。相反，它似乎更适合监测同一地点内的种群变化，以及在梯度较小时。
