Soundscape ecology
Variations in soundscapes as a result of natural phenomena and human endeavor may have wide-ranging ecological effects as many organisms have evolved to respond to acoustic cues that emanate primarily from undisturbed habitats.
However, acoustic ecology, which derives from the founding work of R. Murray Schafer and Barry Truax, primarily focuses on human perception of soundscapes.
[3] Compared to soundscape ecology, the discipline of bioacoustics tends to have a narrower interest in individual species’ physiological and behavioral mechanisms of auditory communication.
This perspective has already highlighted many instances where organisms rely heavily on sound cues generated within their natural environments to perform important biological functions.
According to academic Bernie Krause, soundscape ecology serves as a lens into other fields including medicine, music, dance, philosophy, environmental studies, etc.
It suggests that acoustic signals in the environment should display frequency partitioning as a result of selection acting to maximize the effectiveness of intraspecific communication for different species.
[22] This communication method represents an evolutionary adaptation to the frogs' riparian habitat where running water produces constant low frequency sound.
[4] Although adaptation to acoustic niches may explain the frequency structure of soundscapes, spatial variation in sound is likely to be generated by environmental gradients in altitude, latitude, or habitat disturbance.
For example, birds chorus heavily at dawn and dusk while anurans call primarily at night; the timing of these vocalization events may have evolved to minimize temporal overlap with other elements of the soundscape.
For example, automated recording devices have been used to gather acoustic data in different landscapes across yearlong time scales, and diversity metrics were employed to evaluate daily and seasonal fluctuations in soundscapes across sites.
Anthropophony (the uncontrolled version, is often used synonymously with noise pollution) can emanate from a variety of sources, including transportation networks or industry, and may represent a pervasive disturbance to natural systems even in seemingly remote regions such as national parks.
Against a noisy background, organisms may have trouble perceiving sounds that are important for intraspecific communication, foraging, predator recognition, or a variety of other ecological functions.
[10] For example, noise can increase levels of stress hormones, impair cognition, reduce immune function, and induce DNA damage.
Birds have been used as study organisms in much of the research concerning wildlife responses to anthropogenic noise, and the resulting literature documents many effects that are relevant to other taxa affected by anthropophony.
[26] Research on great tits in an urban environment revealed that male birds inhabiting noisy territories tended to use higher frequency sounds in their songs.
[28] Presumably these higher-pitched songs allow male birds to be heard above anthropogenic noise, which tends to have high energy in the lower frequency range thereby masking sounds in that spectra.
A follow-up study of multiple populations confirmed that great tits in urban areas sing with an increased minimum frequency relative to forest-dwelling birds.
[23] However, not all bird species adjust their songs to improve communication in noisy environments, which may limit their ability to occupy habitats subject to anthropogenic noise.
[33] Male birds that include more low frequency sounds in their song repertoire experience better sexual fidelity from their mates which results in increased reproductive success.
One study focusing on community composition found that habitats exposed to anthropophony hosted fewer bird species than regions without noise, but both areas had similar numbers of nests.
When exposed to high amplitude environmental noise in a laboratory setting, zebra finches, a monogamous species, show a decreased preference for their mated partners.
Furthermore, due to limited dispersal capacity and narrow habitat requirements, insects may be unable to avoid anthropogenic noise by moving to quieter locations.
As a result of interference with communication, insects are at a greater risk of experiencing negative fitness consequences due to impacts on mating, foraging, and survival.
[42] Vibrational signals used by most insects have the majority of their power concentrated below 2kHz, a frequency range that is lower than most airborne communication but has high overlap with many types of anthropogenic noise.
[43] Any reduced ability to recognize and locate mates, avoid predation and other dangers, or forage for food is likely to have negative consequences for survival and reproduction.
[44] Similarly, female Nezara viridula stinkbugs, which use vibrational signals, alter the dominant frequency of their calling song to avoid overlap and interference by vibratory disturbances.
Insect species that utilize this technique include the treehopper Enchenopa Binotata and katydid Copiphora brevirostris, both of which identify gaps in wind noise to initiate signaling during short quiet periods.
[41][51][52] Decreased mating has been observed in multiple species as a result of interfering noise, including Schizocosa ocreata wolf spiders, Graminella nigrifrons leafhoppers, and Dendroctonus pine beetles.
[59][60] Potential consequences of these shifts may lead to cascading effects on higher levels of the food chain, reduced ecological resilience, and the provision of critical ecosystem services such as pollination.
In addition, natural soundscapes can have benefits for human wellbeing and may help generate a distinct sense of place, connecting people to the environment and providing unique aesthetic experiences.
