Lima Steven L
Department of Biology, University of Rochester, 14627, Rochester, NY, USA.
Oecologia. 1985 Apr;66(1):60-67. doi: 10.1007/BF00378552.
Animals often must feed away from protective cover, sometimes at a considerable risk of being preyed upon. Feeding at the maximum rate while away from cover may simultaneously minimize the time spent exposed to predators, but this is not always the case. Under some circumstances, carrying prey items to protective cover before they are consumed will minimize the time spent exposed to predators, whereas feeding at maximum efficiency (staying to eat prey where they are found) will actually increase the time spent exposed to predators. Whether or not there is a conflict between maximizing foraging efficiency and minimizing exposure time, depends upon the travel time to cover relative to the handling time of a prey item; short handling times and/or long travel times are associated with the no-conflict situation, whereas the conflict situation is associated with long handling times and/or short travel times to cover. Free-ranging chickadees foraging at an artificial patch at various distances from cover can distinguish between these two foraging situations. When there is no conflict, they stay and eat at the patch. Their behavior in the conflict situation indicates that they are tradingoff foraging considerations against the risk of predation. When the cost of carrying is low and the benefit gained is high, the chickadees elect to carry items to cover; they tend to stay and eat at the patch when the relative magnitudes of costs and benefits are reversed.
动物常常必须在没有保护掩体的情况下觅食，有时面临着相当大的被捕食风险。在没有掩体的情况下以最快速度进食，可能会同时将暴露于捕食者的时间减至最短，但情况并非总是如此。在某些情况下，在吃掉猎物之前将其带到保护掩体处，会将暴露于捕食者的时间减至最短，而以最高效率进食（在发现猎物的地方停留进食）实际上会增加暴露于捕食者的时间。觅食效率最大化与暴露时间最小化之间是否存在冲突，取决于前往掩体的时间与处理猎物的时间之比；处理时间短和/或前往掩体的时间长与无冲突情况相关，而冲突情况则与处理时间长和/或前往掩体的时间短相关。在距掩体不同距离的人工斑块处觅食的自由放养的山雀能够区分这两种觅食情况。当没有冲突时，它们会留在斑块处进食。它们在冲突情况下的行为表明，它们在权衡觅食考量与被捕食风险。当携带成本低且获得的收益高时，山雀会选择将食物带到掩体处；当成本和收益的相对大小相反时，它们往往会留在斑块处进食。
