Rockwood L L, Hubbell S P
Department of Biology, George Mason University, 22030, Fairfax, VA, USA.
Program in Evolutionary Ecology and Behavior, Department of Biology, University of Iowa, 52242, Iowa City, IA, USA.
Oecologia. 1987 Nov;74(1):55-61. doi: 10.1007/BF00377345.
A month-long study was conducted on the comparative foraging behavior of 20 colonies of the leafcutting ant, Atta cephalotes L. in Santa Rosa National Park, Guanacaste Province, Costa Rica. The study was conducted during the middle of the wet season, when trees had mature foliage and the ants were maximally selective among species of potential host plants. The colonies always gathered leaves from more than a single tree species but on average one species constituted almost half the diet with the remaining species being of geometrically decreasing importance. Colonies exhibited greater diversity in their choice of leaves and lower constancy of foraging when the average quality of resource trees was lower, as predicted by elementary optimal foraging theory. Furthermore, the ants were more selective of the species they attacked at greater distances from the nest. However, the ants sometimes did not attack apparently palatable species, and often did not attack nearby individuals of species they were exploiting at greater distances.A classical explanation for why leafcutting ants exploit distant host trees when apparently equally good trees are nearer, is that the ants are pursuing a strategy of conserving resources to avoid long-term overgrazing pressure on nearby trees. We prefer a simpler hypothesis: (1) Trees of exploited species exhibit individual variation in the acceptability of their leaves to the ants. (2) The abundance of a species will generally increase with area and radial distance from the nest, so the probability that at least one tree of the species will be acceptable to the ants also increases with distance. (3) The ants forage using a system of trunk-trails cleared of leaf litter, which significantly reduces their travel time to previously discovered, high-quality resource trees (by a factor of 4- to 10-fold). (4) Foragers are unware of the total pool of resources available to the colony. Therefore once scouts have chanced upon a tree which is acceptable, the colony will concentrate on harvesting from that tree rather than searching for additional sources of leaves distant from the established trail.
在哥斯达黎加瓜纳卡斯特省圣罗莎国家公园，对20个切叶蚁群落（Atta cephalotes L.）的比较觅食行为进行了为期一个月的研究。该研究在雨季中期进行，此时树木枝叶成熟，蚂蚁对潜在寄主植物种类的选择性最强。蚁群总是从不止一种树木采集树叶，但平均有一种树木构成了近一半的食物来源，其余种类的重要性呈几何级数下降。正如基本最优觅食理论所预测的那样，当资源树的平均质量较低时，蚁群在树叶选择上表现出更大的多样性，觅食的稳定性也较低。此外，蚂蚁在离巢穴较远的距离时，对它们攻击的树木种类更具选择性。然而，蚂蚁有时不会攻击明显可口的树木种类，而且经常不会攻击它们在较远位置采集的树木种类在附近的个体。对于切叶蚁为何在明显同样优质的树木更近时却去利用远处的寄主树，一个经典的解释是，蚂蚁在奉行一种保护资源的策略，以避免对附近树木造成长期的过度啃食压力。我们更倾向于一个更简单的假设：（1）被利用树木种类的树叶对蚂蚁的可接受性存在个体差异。（2）一个树种的丰度通常会随着离巢穴的面积和径向距离增加，所以该树种中至少有一棵树对蚂蚁可接受的概率也会随着距离增加。（3）蚂蚁利用清理了落叶的主干小径系统觅食，这显著减少了它们前往先前发现的优质资源树的行进时间（减少了4到10倍）。（4）觅食者并不知晓蚁群可利用的全部资源库。因此，一旦侦察蚁偶然发现一棵可接受的树，蚁群就会集中从那棵树上采集树叶，而不是去寻找远离既定小径的其他树叶来源。
