Leaf cutter ants are model organisms in studies of central place foraging, but these ants carry smaller than optimal leaf fragments for their body size. Laboratory experiments show that load ratios (leaf fragment mass/ant mass) are higher on extreme downhill trails than on extreme uphill trails, which could explain deviations from optimality in the wild. Here we examine how trail gradient affects load size selection in the field for the first time. We measured load ratios on extreme natural gradients in the mountains of Monteverde, Costa Rica. In general, load ratios were found to be higher on downhill trails than on uphill trails as found in laboratory studies. Not all colonies showed this pattern, indicating that other factors may interact with trail gradient to determine load size selection. The results confirm that extreme trail gradients can contribute to determine optimal load sizes in central place foraging in natural conditions.

中文翻译：

---

轨迹梯度影响野生切叶蚁的负载大小

切叶蚁是中心地点觅食研究中的模式生物，但这些蚂蚁携带的叶子碎片小于其体型的最佳尺寸。实验室实验表明，极端下坡路径上的负载比（叶子碎片质量/蚂蚁质量）高于极端上坡路径，这可以解释与野外最优性的偏差。在这里，我们第一次研究了坡度如何影响现场负载大小的选择。我们测量了哥斯达黎加蒙特维多山区极端自然坡度的负载率。一般而言，在实验室研究中发现，下坡路径的负载率高于上坡路径。并非所有菌落都显示这种模式，这表明其他因素可能与尾迹梯度相互作用以确定负载大小选择。