Soundscape ecology

Soundscape ecology is the study of the acoustic relationships between living organisms, human and other, and their environment, whether the organisms are marine or terrestrial. First appearing in the Handbook for Acoustic Ecology edited by Barry Truax, in 1978, the term has occasionally been used, sometimes interchangeably, with the term acoustic ecology. Soundscape ecologists also study the relationships between the three basic sources of sound that comprise the soundscape: those generated by organisms are referred to as the biophony; those from non-biological natural categories are classified as the geophony, and those produced by humans, the anthropophony.

Increasingly, soundscapes are dominated by a sub-set of anthropophony (sometimes referred to in older, more archaic terminology as "anthropogenic noise"), or technophony, the overwhelming presence of electro-mechanical noise. This sub-class of noise pollution or disturbance may produce a negative effect on a wide range of organisms. 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.

Soundscape ecologists use recording devices, audio tools, and elements of traditional ecological and acoustic analyses to study soundscape structure. Soundscape ecology has deepened current understandings of ecological issues and established profound visceral connections to ecological data. The preservation of natural soundscapes is now a recognized conservation goal.

As an academic discipline, soundscape ecology shares some characteristics with other fields of inquiry but is also distinct from them in significant ways. For instance, acoustic ecology is also concerned with the study of multiple sound sources. However, acoustic ecology, which derives from the founding work of R. Murray Schafer and Barry Truax, primarily focuses on human perception of soundscapes. Soundscape ecology seeks a broader perspective by considering soundscape effects on communities of living organisms, human and other, and the potential interactions between sounds in the environment. Compared to soundscape ecology, the discipline of bioacoustics tends to have a narrower interest in individual species' physiological and behavioral mechanisms of auditory communication. Soundscape ecology also borrows heavily from some concepts in landscape ecology, which focuses on ecological patterns and processes occurring over multiple spatial scales. Landscapes may directly influence soundscapes as some organisms use physical features of their habitat to alter their vocalizations. For example, baboons and other animals exploit specific habitats to generate echoes of the sounds they produce.

The function and importance of sound in the environment may not be fully appreciated unless one adopts an organismal perspective on sound perception, and, in this way, soundscape ecology is also informed by sensory ecology. Sensory ecology focuses on understanding the sensory systems of organisms and the biological function of information obtained from these systems. In many cases, humans must acknowledge that sensory modalities and information used by other organisms may not be obvious from an anthropocentric viewpoint. This perspective has already highlighted many instances where organisms rely heavily on sound cues generated within their natural environments to perform important biological functions. For example, a broad range of crustaceans are known to respond to biophony generated around coral reefs. Species that must settle on reefs to complete their developmental cycle are attracted to reef noise while pelagic and nocturnal crustaceans are repelled by the same acoustic signal, presumably as a mechanism to avoid predation (predator densities are high in reef habitats). Similarly, juvenile fish may use biophony as a navigational cue to locate their natal reefs, and may also be encouraged to resettle damaged coral reefs by playback of healthy reef sound. Other species' movement patterns are influenced by geophony, as in the case of the reed frog which is known to disperse away from the sound of fire. In addition, a variety of bird and mammal species use auditory cues, such as movement noise, in order to locate prey. Disturbances created by periods of environmental noise may also be exploited by some animals while foraging. For example, insects that prey on spiders concentrate foraging activities during episodes of environmental noise to avoid detection by their prey. These examples demonstrate that many organisms are highly capable of extracting information from soundscapes.

According to academic Bernie Krause, soundscape ecology serves as a lens into other fields including medicine, music, dance, philosophy, environmental studies, etc. (the soundscape). Krause sees the soundscape of a given region as the sum of three separate sound sources (as described by Gage and Krause) defined as follows:

According to Krause various combinations of these acoustic expressions across space and time generate unique soundscapes.^{[citation needed]}

Soundscape ecologists seek to investigate the structure of soundscapes, explain how they are generated, and study how organisms interrelate acoustically. A number of hypotheses have been proposed to explain the structure of soundscapes, particularly elements of biophony. For instance, an ecological theory known as the acoustic adaptation hypothesis predicts that acoustic signals of animals are altered in different physical environments in order to maximize their propagation through the habitat. In addition, acoustic signals from organisms may be under selective pressure to minimize their frequency (pitch) overlap with other auditory features of the environment. This acoustic niche hypothesis is analogous to the classical ecological concept of niche partitioning. 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. Observations of frequency differentiation among insects, birds, and anurans support the acoustic niche hypothesis. Organisms may also partition their vocalization frequencies to avoid overlap with pervasive geophonic sounds. For example, territorial communication in some frog species takes place partially in the high frequency ultrasonic spectrum. This communication method represents an evolutionary adaptation to the frogs' riparian habitat where running water produces constant low frequency sound. Invasive species that introduce new sounds into soundscapes can disrupt acoustic niche partitioning in native communities, a process known as biophonic invasion. 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. These gradients may alter the relative contributions of biophony, geophony, and anthrophony to the soundscape. For example, when compared with unaltered habitats, regions with high levels of urban land-use are likely to have increased levels of anthrophony and decreased physical and organismal sound sources. Soundscapes typically exhibit temporal patterns, with daily and seasonal cycles being particularly prominent. These patterns are often generated by the communities of organisms that contribute to biophony. 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.