Layne John E, Chen P W, Gilbert Cole
Department of Entomology, Cornell University, Ithaca, NY 14853, USA.
J Exp Biol. 2006 Nov;209(Pt 21):4295-303. doi: 10.1242/jeb.02529.
The elevation of objects in the visual field has long been recognized as a potential distance cue, but it has been demonstrated to a reasonable extent in only four species: humans, frogs, fiddler crabs and backswimmers. Many tiger beetles hunt in flat, sandy areas, and their eyes show "flat-world" adaptations, such as an extended visual streak of higher acuity that corresponds to the horizon. They are therefore possible candidates for the use of elevation as a cue for distance. We tested this empirically and with simulation. In a behavioral prey selection paradigm, in which starved beetles were presented moving prey-targets having different size, speed and elevation, the beetles showed a strong preference for large targets when these were low in the visual field and a weaker preference for small targets when these were near the horizon. Striking of targets above the horizon was reduced compared to sub-horizontal targets, and lacked the size-elevation interaction. We simulated these empirical results with a model that converted elevation to distance, and used distance to estimate the absolute size of the targets. Simulated strike probability was then determined by the similarity between this absolute size and an independently confirmed preferred prey size. The results of the simulation model matched the empirical data as well as the best statistical model of the behavioral results. While some aspects of the model, and the beetles' behavior, differ from the strict geometry of the "elevation hypothesis", our results nevertheless indicate that tiger beetles use elevation to estimate distance to prey, and that it is therefore one of the determinants of prey selection.
视野中物体的高度长期以来一直被认为是一种潜在的距离线索，但仅在四种物种中得到了一定程度的验证：人类、青蛙、招潮蟹和仰泳蝽。许多虎甲在平坦的沙地捕猎，它们的眼睛呈现出“平面世界”的适应性特征，比如有一条延伸的视觉条纹，其敏锐度更高，对应着地平线。因此，它们有可能利用高度作为距离线索。我们通过实验和模拟对此进行了测试。在一个行为猎物选择范式中，向饥饿的虎甲展示具有不同大小、速度和高度的移动猎物目标，当大目标处于视野下方时，虎甲对其表现出强烈偏好，而当小目标靠近地平线时，虎甲对其偏好较弱。与水平以下的目标相比，攻击地平线以上目标的情况减少，并且不存在大小 - 高度相互作用。我们用一个将高度转换为距离并利用距离估计目标绝对大小的模型模拟了这些实验结果。然后，模拟的攻击概率由这个绝对大小与独立确认的偏好猎物大小之间的相似性决定。模拟模型的结果与实验数据以及行为结果的最佳统计模型相匹配。虽然模型的某些方面以及虎甲的行为与“高度假设 ”的严格几何原理不同，但我们的结果仍然表明，虎甲利用高度来估计到猎物的距离，因此它是猎物选择的决定因素之一。
