Introduction

Several signallers and receivers sharing the same active signalling space constitute a communication network. This type of environment imposes additional selection pressures on both signallers and receivers other than those classically considered in signaller–receiver dyads. In this chapter, we shall discuss how communication networks influence the behaviour of a signaller and, more specifically, the effect of an audience (defined below) on signalling behaviour.

An individual signaller has to cope with two main issues when signalling in a network: (a) it has to compete or cooperate with other signallers, and (b) it has to deal with the presence of several receivers. Signalling at the same time as other individuals poses a problem for the signaller: how does it ensure that its specific signal is detected by a receiver when other conspecifics are signalling? Signallers solve or minimize this problem by either cooperating or competing for the signal broadcast space. For example, in frog and insect choruses, individuals time their signals to avoid acoustic interference (e.g. alternating their calls) or compete for call order in the chorus (Gerhardt & Huber, 2002; Ch. 13). At the community level, different species with similar signals may broadcast their signals at different times of the day (Endler, 1992).

The presence of several receivers presents two additional problems for the signaller. The first is how to direct the signal to a specific receiver. For example, bird song often has a range that encompasses several neighbouring territories.