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, 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.
Background
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. 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.
Terminology
According to academic Bernie Krause, soundscape ecology serves as a lens into other fields including medicine, music, dance, philosophy, environmental studies, etc.. Krause sees the soundscape of a given region as the sum of three separate sound sources defined as follows:- Geophony, from the Greek prefix, geo, meaning earth-related, and phon, meaning sound, is a neologism used to describe one of three possible sonic components of a soundscape. It relates to the naturally occurring non-biological sounds coming from different types of habitats, whether marine or terrestrial. Typically, geophony refers to the sounds of natural forces, such as water, wind, and thunder, occurring in wild, relatively undisturbed habitats. But geophony is not limited to that narrow definition since these audio sources can be experienced nearly everywhere the effects of wind and water are expressed.
- Biophony is a term introduced by Krause, who in 1998, first began to express the soundscape in terms of its acoustic sources. The biophony refers to the collective acoustic signatures generated by all sound-producing organisms in a given habitat at a given moment. It includes vocalizations that are used for conspecific communication in some cases. Biophony consists of the Greek prefix, bio, meaning life, and the suffix, phon, meaning sound, is a neologism used to describe the collective sound that vocalizing animals create in each given environment. It explores new definitions of animal territory as defined by biophony, and addresses changes in density, diversity, and richness of animal populations. Mapping soundscapes can help to illustrate possible driving mechanisms and provide a valuable tool for urban management and planning. However, quantifying biophony across urban landscapes has proven difficult in the presence of anthrophony, or sounds generated by humans. The metric percent biophony can be used to quantify biophony while avoiding noise bias. The complete absence of biophony or geophony in a given biome would be expressed as dysphonia. The niche hypothesis, an early version of the term biophony, describes the acoustic bandwidth partitioning process that occurs in still-wild biomes by which non-human organisms adjust their vocalizations by frequency and time-shifting to compensate for vocal territory occupied by other vocal creatures. Thus each species evolves to establish and maintain its own acoustic bandwidth so that its voice is not masked. For instance, notable examples of clear partitioning and species discrimination can be found in the spectrograms derived from the biophonic recordings made in most uncompromised tropical and subtropical rain forests. Additional studies with certain insects and amphibians tend to confirm the hypothesis.
- Anthropophony is another term introduced by Krause along with colleague, Stuart Gage. It represents human generated sound from either humans, themselves, or the electro-mechanical technologies they employ. The term, anthropophony, consisting of the Greek prefix, anthropo, meaning human, and the suffix, phon, meaning sound is a neologism used to describe all sound produced by humans, whether coherent, such as music, theatre, and language, or incoherent and chaotic such as random signals generated primarily by electromechanical means. Anthropophony is divided into two sub-categories. Controlled sound, such as music, language, and theatre, and chaotic or incoherent sound sometimes referred to as noise.
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 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.