The role of chromatic and achromatic signals for fruit detection by birds
The role of chromatic and achromatic signals for fruit detection by birds
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DOI：
10.1093/beheco/arl011
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发表时间：
2006-09-01
影响因子：
2.4
通讯作者：
Avery, Michael L.
中科院分区：
文献类型：
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作者：
Schaefer, H. Martin;Levey, Douglas J.;Avery, Michael L.
果实成熟过程中的颜色变化通常被视为一种适应，以增加种子传播的信号效力。植物可以通过增强果实和背景之间的彩色（波长相关）和/或非彩色（强度相关）对比来增加信号功效。为了评估这些对比度如何决定水果信号的可检测性，我们在2025 m2的鸟舍中用自由飞行的乌鸦（Corvus ossifragus）在自然条件下进行了2次实验。乌鸦首先寻找人造红色和黑色水果，并从更远的距离发现红色水果。由于人造红色水果比人造黑色水果对树叶有更高的彩色和更低的非彩色对比，乌鸦显然优先考虑彩色对比。因此，在成熟期间果实颜色从红色到黑色的常见变化不会增加对乌鸦的信号效力。在第二次试验中，乌鸦在树叶和沙子的背景下寻找反射紫外线的黑蓝莓。在树叶的映衬下，反射紫外线的浆果比黑色浆果有更高的彩色和非彩色对比度，乌鸦从更远的距离就能探测到它们。对沙子，紫外线反射浆果低消色差对比和黑色浆果低彩色对比。乌鸦同样检测到两种水果类型，这表明他们使用彩色对比来检测紫外线反射浆果和无色对比来检测黑色浆果。鸟类在树叶中寻找人造红色水果时优先考虑色彩对比，而在沙滩上寻找蓝莓时则不然。我们认为，彩色和非彩色对比度的相对重要性取决于背景的彩色和非彩色方差。信号感知模型可以通过引入背景特异性效应来改进。
Fruit color changes during ripening are typically viewed as an adaptation to increase signal efficacy to seed dispersers. Plants can increase signal efficacy by enhancing chromatic (wavelength related) and/or achromatic (intensity related) contrasts between fruit and background. To assess how these contrasts determine the detectability of fruit signals, we conducted 2 experiments with free-flying crows (Corvus ossifragus) under seminatural conditions in a 2025 m(2) aviary. Crows searched first for artificial red and black fruits and detected red fruits from a larger distance. Because artificial red fruits had higher chromatic and lower achromatic contrasts against foliage than artificial black fruits, crows apparently prioritized chromatic contrasts. Thus, the common change in fruit color from red to black during ripening does not increase signal efficacy to crows. In a second trial, crows searched for UV-reflecting and black blueberries (Vaccinum myrtillus) against backgrounds of foliage and sand. Against foliage, UV-reflecting berries had higher chromatic and achromatic contrasts than black berries, and crows detected them from a larger distance. Against sand, UV-reflecting berries had low achromatic contrasts and black berries low chromatic contrasts. Crows detected both fruit types equally, suggesting that they used chromatic contrasts to detect UV-reflecting berries and achromatic contrasts to detect black berries. Birds prioritized chromatic contrasts when searching for artificial red fruits in foliage but not when searching for blueberries on sand. We suggest that the relative importance of chromatic and achromatic contrasts is contingent on the chromatic and achromatic variance of the background. Models of signal perception can be improved by incorporating background-specific effects.