Johnstone R A
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, United Kingdom.
Proc Natl Acad Sci U S A. 1999 Oct 26;96(22):12644-9. doi: 10.1073/pnas.96.22.12644.
Young birds and mammals frequently solicit food by means of extravagant and apparently costly begging displays. Much attention has been devoted to the idea that these displays are honest signals of need, and that their apparent cost serves to maintain their honesty. Recent analyses, however, have shown that the cost needed to maintain a fully informative, honest signal may often be so great that both offspring (signaler) and parent (receiver) would do better to refrain from communication. This apparently calls into question the relevance of the costly signaling hypothesis. Here, I show that this argument overlooks the impact of sibling competition. When multiple signalers must compete for the attention of a receiver (as is commonly the case in parent-offspring interactions), I show that (all other things being equal) individual equilibrium signal costs will typically be lower. The greater the number of competitors, the smaller the mean cost, though the maximum level of signal intensity employed by very needy signalers may actually increase with the number of competitors. At the same time, costs become increasingly sensitive to relatedness among signalers as opposed to relatedness between signalers and receivers. As a result of these trends, signaling proves profitable for signalers under a much wider range of conditions when there is competition (though it is still likely to be unprofitable for receivers).
幼鸟和哺乳动物经常通过夸张且看似代价高昂的乞食行为来获取食物。人们对这些行为是需求的诚实信号这一观点给予了很多关注，并且它们看似高昂的代价有助于维持其诚实性。然而，最近的分析表明，维持一个完全信息性、诚实信号所需的代价可能常常过高，以至于后代（信号发送者）和父母（信号接收者）都最好避免交流。这显然对代价信号假说的相关性提出了质疑。在此，我表明这一论点忽视了同胞竞争的影响。当多个信号发送者必须竞争信号接收者的关注时（亲子互动中通常如此），我表明（在其他条件相同的情况下）个体均衡信号代价通常会更低。竞争者数量越多，平均代价越小，不过非常饥饿的信号发送者所采用的最大信号强度水平实际上可能会随着竞争者数量的增加而上升。与此同时，代价对信号发送者之间的亲缘关系变得越来越敏感，而不是信号发送者与信号接收者之间的亲缘关系。由于这些趋势，当存在竞争时，信号传递在更广泛的条件下对信号发送者来说是有利可图的（尽管对信号接收者来说可能仍然无利可图）。
