Fruit choice in migrating North American birds : field and aviary experiments
Fruit choice in migrating North American birds : field and aviary experiments
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北美迁徙鸟类的水果选择：田野和鸟舍实验
作者：
C. Whelan;M. Willson
我们通过实验研究了水果呈现的几个方面如何影响候鸟（无论是自由放养还是圈养）的水果偏好。我们发现，自由放养的鸟类更喜欢特定植物物种的可获取果实，而不是无法获取的果实，并且对田间可获取性的操纵可以成为衡量植物物种之间对果实偏好的相对强度的有用工具。对于两种植物物种的果实，双色展示比单色展示有更多的点击次数（实验展示中至少拿走一个水果）和更大比例的水果被移除（从所有实验展示中）。异种水果作物的接近度（不同植物物种的水果的单独或同时相遇）对水果偏好没有明显影响。当同时提供多种具有一系列营养奖励的物种时，鸟类对特定植物物种的果实表现出明显的偏好，但这种偏好与果皮化学的总体特征（例如脂质百分比或糖百分比）没有明确的对应关系。当两种植物的果实在人造水果展示架上分别或同时遇到时，自由放养和圈养的候鸟的反应与检查水果偏好的实验相似。圈养鸟类在个体、实验处理和重复处理之间做出了一致的选择。这些发现表明，水果呈现的环境背景会对候鸟的水果偏好产生强烈影响，这应该有助于鸟类传播者和结果植物之间进化相互作用的扩散性质。这种相互作用的分散性反过来可能会降低识别鸟类果实选择对结果性状选择的影响的能力。最后，我们提出了一种检查本地与外来植物物种在吸引鸟类传播者方面的相对竞争能力的方法，并指出如何将这些知识应用于生物控制计划以根除有问题的外来植物物种。
We experimentally examined how several aspects of fruit presentation affected fruit preferences of migrating birds, both free-ranging and captive. We found that freeranging birds prefer accessible over inaccessible fruit of a given plant species, and that manipulation of accessibility in the field can be a useful tool for measuring the relative strength of fruit preferences between plant species. Bicolored diplays had a greater number of hits (experimental displays with at least a single fruit taken) and a greater proportion of fruits removed (from all experimental displays) than unicolored displays for fruit of two plant species. Proximity of heterospecific fruit crops (separate vs simultaneous encounter of fruits of different plant species) had no evident effect on fruit preferences. Birds showed clear preferences for fruit of particular plant species when a variety of species exhibiting a range of nutritional rewards were offered simultaneously, but the preferences had no clear correspondence to gross characteristics of pericarp chemistry, such as percent lipid or percent sugar. Both free-ranging and captive migrant birds responded similarly to experiments examining fruit preferences when the fruit of two plant species were encountered separately or simultaneously on artificial fruit displays. The captive birds made consistent choices among individuals, experimental treatments, and replicates of treatments. These findings demonstrate that environmental context of fruit presentation can have strong effects on fruit preferences of migrating birds, which should contribute to the diffuse nature of the evolutionary interaction between bird dispersers and fruiting plants. The diffuse nature of this interaction may in turn decrease the ability to identify the effect of bird fruit choice on selection on fruiting traits. Finally, we suggest a method for examining the relative competitive abilities of native versus exotic plant species in attracting bird dispersers, and indicate how this knowledge can be applied in biological control programs for eradicating problem exotic plant species.