by Amanda Franklin
If you have ever gone to see a band, I’m sure you’ll remember how loud the music is and how hard it is to talk to your friend during the show. At least when you leave, you can return to talking at a normal volume. But what about if there was that much background noise all the time? It would be extremely difficult to talk to anyone and we would need to reconsider how we communicate. This is effectively what has happened to many animals when human changes to the environment interfere with their communication systems.
Animals communicate with one another using a variety of signals. A signal is a characteristic (e.g., frog call, bird tail length, moth scent emission) that conveys information from the signaler to the receiver and provides a benefit to the signaler. For example, the iridescent blue rings on blue ringed octopus signal aggression and toxicity. The blue ringed octopus benefits from sending this signal because it can avoid an attack from another animal. Human changes to the environment (e.g. increasing water cloudiness through dredging) could decrease the effectiveness of this signal and undermine the signalling system.
In fact, there are several research studies that show the detrimental effects of increasing water cloudiness on animal visual communication. Water cloudiness can increase due to algal blooms (from the addition of fertilisers to the water) or by increases in suspended sediment (from erosion or dredging). These increases can place strain on fish mating systems and influence important mating behaviours. For example, in turbid environments female sticklebacks switch from using visual cues to chemical cues. This changes which male they will choose to mate with. Such changes can dramatically alter the direction of evolution of the species, as has been demonstrated in Lake Victoria in East Africa. Here, increased turbidity caused two different cichlid fish species to effectively become only one species, due to changes in female mate choice.
Aquatic systems can also be affected by chemical contaminants. Many aquatic animals use chemicals to communicate with one another. The addition of chemical pollutants (e.g. pesticides, heavy metals, and acidification) can disrupt chemical communication systems involved in predator-prey and reproductive behaviours. For example, many fish rely on chemicals to locate and recognise other fish for shoaling. Exposure to low doses of a common contaminant causes killifish to be excluded by other killifish. This disruption to shoaling behaviours can have serious implications for food location and defence against predators. In many cases these effects occur at low concentrations of pollutants. Thus, our current safe concentrations of these pollutants may already be disrupting signalling systems.
The effects of environmental change on communication systems can also be observed in terrestrial systems. In urban environments, there are many artificial sounds that are not present in natural environments (e.g. cars, construction, airports). These sounds provide a background noise that animals must compete with when trying to send acoustic signals. Many species are not able to adapt their signals in noisy environments; this can lead to the collapse of their mating system. However, some species can change their signalling behaviours so that their acoustic signal is transmitted in noisy, urban environments. For example, male birds that sing shorter, higher pitched songs in urban areas tend to be preferred by females, likely because their call can be heard over the low pitched background noise. This could lead to only small species or small individuals surviving in urban environments, because larger birds generally sing lower pitched songs. The changes in species composition will also have flow on effects for pollination and seed dispersal.
Animals use communication for many activities including finding food, avoiding predators, resolving conflicts and selecting mates. Because these activities are an important part of everyday life for many species, it is likely that human influenced environmental changes are affecting communication systems in a huge range of species around the globe. As humans impact more areas of the planet we need to investigate how a variety of different species will respond. This will help us to understand species evolution, biodiversity loss and how species ranges may change in the future. Overall, it is an exciting research field that can provide valuable information to help us conserve species diversity in the face of global change.
Amanda Franklin is a 2012 fellow of the Fulbright Science and Technology Award program, from Australia, and a PhD candidate in Animal Behaviour and Evolution at Tufts University.