Whittingham M, Markland H
Edward Grey Institute of field Ornithology, Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
Oecologia. 2002 Feb;130(4):637-644. doi: 10.1007/s00442-001-0850-z. Epub 2002 Feb 1.
Few studies to date have considered the effect of substrate on the functional response of an organism feeding on prey of varying visibility. Intake rates of lone captive canaries, Serinus canarius L., were measured at varying seed densities on patches of either earth or short grass (<1 cm). Experiment 1, using pale seeds, found intake rates were significantly higher and search times significantly lower on earth than on grass. Two measures of crypticity (contrast in light reflectance as measured using a spectrophotometer and an experiment with humans) found pale seeds to be more visible on earth. The results from experiment 1 could be explained by this difference in crypsis. Experiment 2 used identical seeds to those in experiment 1 except they were dyed to match their backgrounds. The two measures of crypticity both found that black seeds were less visible on earth than green seeds were on grass. However, intake rates were still significantly higher on earth than grass. Seed colour preference, vegetation impeding movement, and differences in vigilance rates or seed accessibility could not explain this result. We discuss three other potentially explanatory mechanisms, the most likely of which was the greater surface area needed for scanning created by the structure of grass. Crucially, regardless of the mechanism(s) involved, many vegetated substrates share similar properties with grass (structural complexity and shiny surfaces which reflect light) and so the outcome of our findings are likely to extend to many natural situations. Conservationists wishing to encourage granivorous birds should consider enhancing food accessibility by providing uniform substrates, such as bare earth, for them to forage on. In addition, behaviour-based models should incorporate the effects of habitat into their equations of the functional response.
迄今为止，很少有研究考虑底物对以不同可见度猎物为食的生物体功能反应的影响。在铺有泥土或矮草（<1厘米）的斑块上，以不同种子密度测量单独圈养的金丝雀（Serinus canarius L.）的摄入量。实验1使用浅色种子，发现泥土上的摄入量显著更高，搜索时间显著低于草地上的。两种隐蔽性测量方法（使用分光光度计测量光反射率对比度以及一项针对人类的实验）发现浅色种子在泥土上更易被看见。实验1的结果可以用这种隐蔽性差异来解释。实验2使用了与实验1相同的种子，只是将它们染色以匹配其背景。两种隐蔽性测量方法都发现黑色种子在泥土上比绿色种子在草地上更不易被看见。然而，泥土上的摄入量仍然显著高于草地上的。种子颜色偏好、植被阻碍移动以及警惕率或种子可及性的差异都无法解释这一结果。我们讨论了其他三种可能的解释机制，其中最有可能的是草的结构造成扫描所需的更大表面积。至关重要且无论涉及何种机制，许多植被底物与草具有相似的特性（结构复杂性和反射光的闪亮表面），因此我们的研究结果可能适用于许多自然情况。希望鼓励食谷鸟类的保护主义者应考虑通过提供统一的底物，如裸地，来提高食物可及性，以便它们觅食。此外，基于行为的模型应将栖息地的影响纳入其功能反应方程中。
