Data from: Roses are red, violets are blue - so how much replication should you do? An assessment of variation in the colour of flowers and birds

After years of qualitative and subjective study, quantitative colour science is now enabling rapid measurement, analysis and comparison of colour traits. However, it has not been determined how many replicates one needs to accurately quantify a species’ colours for studies aimed at broad cross-species trait comparison. We address this major methodological knowledge gap. We first quantified and assessed the variance in colour within and between species. Reflectance spectra of flowers from ten plant species and plumage of 20 bird species were measured using a spectrometer, and reflectance (i.e. brightness) and tetrahedral colour-space coordinates were calculated. ANOVA analyses indicate that there is far more variation in the colours of birds and flowers between species (> 77 %) than within species. A Mean Absolute Deviation from the Mean test was applied to indicate the sampling replication required for each species. Tetrahedral coordinates were sampled precisely with only one individual per species. Greater replication was needed to sample reflectance with the desired precision, particularly for darker coloured species. Our findings will allow researchers to allocate their sampling effort in a way that maximises the precision of their colour data collection. The fact that only a few replicates per species are necessary will greatly facilitate broad cross-species comparisons of colour in the future.

经过多年定性与主观性研究，定量色彩科学（quantitative colour science）如今已可实现色彩性状的快速测量、分析与比较。然而，针对旨在开展跨物种性状广泛比较的研究而言，准确量化某一物种色彩所需的重复样本数量，目前仍未明确。本研究旨在填补这一重要的方法学认知空白。我们首先量化并评估了物种内部与物种间的色彩变异情况：借助光谱仪（spectrometer）测量了10种植物的花朵反射光谱与20种鸟类的羽毛反射光谱，并计算得到反射率（reflectance，即亮度）与四面体色彩空间（tetrahedral colour-space）坐标。方差分析（ANOVA）结果显示，鸟类与植物花朵的色彩变异主要来源于物种间（占比超77%），而非物种内部。本研究采用均值绝对偏差检验（Mean Absolute Deviation from the Mean test）来确定各物种所需的采样重复次数：仅需每个物种的单个个体，即可精准获取四面体色彩空间坐标；若要以预设精度采样反射率，则需要更多重复样本，对于颜色较深的物种而言尤为如此。本研究结果可帮助研究人员合理分配采样工作量，以最大化色彩数据采集的精度。仅需少量物种重复样本即可满足研究需求这一结论，将在未来极大地推动跨物种色彩性状的广泛比较研究。