Data from: Extended phenotypes and foraging restrictions: ant nest entrances and resource ingress in leaf-cutting ants
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Several factors may restrict the acquisition of food to below the levels predicted by the optimization theory. However, how the design of structures that animals build for foraging restrict the entry of food are less known. Using scaling relationships we determined whether the design of the entrances of leaf-cutting ant nests restricts resource input into the colony. We measured nests and foraging parameters in 25 nests of Atta cephalotes in a tropical rain forest. Ant flux was reduced to up to 60% at nest entrances. The width of all entrances per nest increased at similar rates as nest size, but the width of nest entrances increased with the width of its associated trail at rates below those expected by isometry. The fact that entrance widths grow slower than trail widths suggests that the enlargement of entrance holes does not reach the dimensions needed to avoid delays when foraging rates are high and loads are big. The enlargement of nest entrances appears to be restricted by the digging effort required to enlarge nest tunnels, and by increments in the risk of inundation, predator/parasitoid attacks, and microclimate imbalances inside the nest. The design of the extended phenotypes can also restrict the ingress of food into the organisms, offering additional evidence to better understand eventual controversies between empirical data and the foraging theory.
多种因素可使食物获取量低于优化理论（optimization theory）的预测值，但动物为觅食所建造的结构设计如何限制食物进入的相关机制，目前仍尚不明确。本研究借助标度关系（scaling relationships），探究切叶蚁（leaf-cutting ant）巢穴入口的设计是否会限制蚁群的资源输入。我们在热带雨林中对25个塞氏切叶蚁（Atta cephalotes）的巢穴及觅食相关参数开展了实测。结果显示，巢穴入口处的蚁群流量可被降低至多60%。单个巢穴的所有入口宽度随巢穴规模以相近速率增长，但巢穴入口宽度随其关联蚁路宽度的增长速率低于等距生长（isometry）的预期值。入口宽度的增长慢于蚁路宽度这一现象表明，当觅食速率较高且负载较大时，巢穴入口的扩宽并未达到可避免通行拥堵的尺寸。巢穴入口的扩宽似乎受到两方面约束：一是扩宽巢穴隧道所需的挖掘工作量，二是巢穴内淹没风险、捕食者/寄生性天敌攻击风险以及微气候失衡状况的加剧。扩展表型（extended phenotypes）的设计同样可能限制食物进入生物体内部，这为进一步理解觅食理论与实证数据间的潜在争议提供了新的佐证。
