When we first hear the word pollution, our brains fill with images of toxic sludge, industrial chimneys releasing dense black fumes, and pictures of baby seals covered in crude oil. In this human dominated era, how can you blame us? It seems like every other month there’s some catastrophic failure that results in a biological community being decimated. Unfortunately for all of Earth’s inhabitants, pollution and humanity go hand in hand. For years now, ecologists have realized that pollution doesn’t just take the form of a physical matter like oil, heavy metals and industrial exhaust, but sound as well. So besides polluting natural environments with these physical substances, the noises our cars, trains, and guitars make also can fundamentally change how ecosystems function.
Many animals use sound to detect mates, predators and food. Loud anthropogenic noises may make it more difficult for some organisms to function, and these seemingly small interactions become magnified when the entire trophic system is at play. In a standout publication by Brandon Barton and his team earlier this year, the impact of noise pollution was analyzed using a tripartite ecological relationship between ladybugs (predator), soybean aphids (prey and herbivore) and soybean plants (primary producer). Using speakers, these scientists played different types of music and urban sounds on mesocosms containing all three organisms. Their results are actually quite interesting.
In the 18-hour feeding trials, ladybugs ate less aphids in the mesocosms infiltrated by urban sounds and rock and roll. Other genres of music at the same volume had no effect. In the trophic experiment, the music was played for two weeks in each mesocosm. At the end of the two weeks, the researchers quantified plant growth, again revealing the important trophic interactions at play. Again, our ladybug predators ate fewer prey, allowing more aphid herbivores to feed on the soybean plants. With higher aphid density, plant growth was reduced compared to control mesocosms with no music playing.
The actual mechanism of sound disturbance is unknown, but it is certain to reduce predation of aphids by ladybugs. Without ladybugs in the experimental mesocosms plant growth and aphid density was unchanged. This is the magnification I was talking about! The ecological alteration of just one organism in a tripartite relationship can radiate throughout the entire system. The fact that rock and roll along with urban sounds changed the ecology of this system compared to other genres of music is fascinating. The tones and frequencies at play with the sounds that did reduce predation might be more detectable by the predators here, but again, the specific mechanism is unknown.
This study quantified how plant growth might be reduced with noise pollution, but as many plant-herbivore-predator papers reveal, soil fungi receive fewer sugars from plants that are more reduced by herbivores. So without a doubt, noise pollution alters organisms that live both above and below the forest floor. Who would have thought AC/DC could change the way ecosystems function? Ironically, the classic rock band has a song entitled, “Rock and Roll Ain’t Noise Pollution,” but they really couldn’t be more wrong.