Communication: The sender's point of view

When an animal needs to communicate with a conspecfic, five basic factors affect the animal's signal choice:

1. Communicatory modes available (sender can produce signal in mode, sender can receive).
   
   Obviously, animals cannot communicate if either the signal cannot be produced or perceived. It is more interesting to consider the conditions under which communication may have initially evolved. Two hypotheses are reasonable:
   • Perception first evolved in an environmental circumstance, so that primitive organisms could touch, see, feel, smell and perhaps hear their way in the environment. Once the perceptual mechanisms had evolved, then individuals with mutations causing them to produce signals might be favored; over time natural selection resulted in signals with specific meanings.
   • Animals adapted intracellelular chemical signalling, evolved to regulate cellular processes, for signalling between cells (hormones) or between organisms (pheromones).
     
     
2. Energy required to produce signal.
   
   The energy that it takes to make a signal is important because it represents a real cost of communication. An animal must balance its need to communicate versus other uses it might have for that energy. In some cases, the receiver uses the energetic value of the signal as an important component of the information of the signal. For example, a female looking for a mate may choose the male which is able to invest the greatest energy into producing attractive signals, such as vocalizations. This male could have the best genes, because he has been able to accumulate the needed energy for energy-consuming communication.
   
   
3. Distance signal needs to travel
   
   Broadcasting a signal too widely can have serious costs in unnecessary expenditure of energy and attraction of unwanted attention. Some signal types are better for long-distance communication while others are better for communication with nearby animals. For example, elephants use infrasound to communicate over long distances, while mice use ultrasound in communicating with their pups. Infrasound requires high energy to produce but travels far, while ultrasound has a more limited range, reducing the likelihood of attracting predators.
   
   
4. Competing signals and noise
   
   Just like television stations, which much use different wavelengths for their signals to avoid interference, animals evolve to avoid interference from other species. Strategies to avoid interference include selecting times of day for communication when fewer other species are communicating, choosing less-used modes of communication, and evolving to partition the communication channel among species.
   
   
5. Attracting unwanted attention, such as competitors or predators
   
   Any signal an animal makes can be used by any other animal. Firefly mating flashes turn into beacons for other, predatory, firefly species. Defensive odors in ants become attractants for parasites. Vocal signals allow predators to home in on birds. This is a real cost of communication, a cost that an animal must weigh before producing a signal.

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copyright ©2001 Michael D. Breed, all rights reserved