Soundscape ecology

As an academic discipline, soundscape ecology shares some characteristics with other fields of inquiry but is also distinct from them in significant ways. 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. (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: • 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 (PB) 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 (from the Greek meaning the inability to produce a proper collective voice in this case). The niche hypothesis (also known as the acoustic niche hypothesis; ANH), 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. According to Krause various combinations of these acoustic expressions across space and time generate unique soundscapes. 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. 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. ==Methods==

Acoustic information describing the environment is the primary data required in soundscape ecology studies. Technological advances have provided improved methods for the collection of such data. Automated recording systems allow for temporally replicated samples of soundscapes to be gathered with relative ease. Data collected from such equipment can be extracted to generate a visual representation of the soundscape in the form of a spectrogram. These techniques may be especially important for the study of rare or elusive species that are especially difficult to monitor in other ways. ==Insights from soundscape ecology: anthropophony==

Although soundscape ecology has only recently been defined as an independent academic discipline (it was first described in 2011 and formalized at the first meeting of the International Society of Ecoacoustics, held in Paris in 2014), many earlier ecological investigations have incorporated elements of soundscape ecology theory. For instance, a large body of work has focused on documenting the effects of anthropophony on wildlife. 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. In addition to interfering with ecologically important sounds, anthropophony can also directly affect the biological systems of organisms. Noise exposure, which may be perceived as a threat, can lead to physiological changes. Although much of the research on anthropogenic noise has focused on behavioral and population-level responses to noise disturbance, these molecular and cellular systems may prove promising areas for future work. ==Anthropophony and birds==

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. Birds may be particularly sensitive to noise pollution given that they rely heavily on acoustic signals for intraspecific communication. Indeed, a wide range of studies demonstrate that birds use altered songs in noisy environments. 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. In addition, this study suggests that noisy urban habitats host birds that use shorter songs but repeat them more rapidly. In contrast to frequency modulations, birds may simply increase the amplitude (loudness) of their songs to decrease masking in environments with elevated noise. Experimental work and field observations show that these song alterations may be the result of behavioral plasticity rather than evolutionary adaptations to noise (i.e., birds actively change their song repertoire depending on the acoustic conditions they experience). In fact, avian vocal adjustments to anthropogenic noise are unlikely to be the products of evolutionary change simply because high noise levels are a relatively recent selection pressure. In some species, individual birds establish a relatively rigid vocal repertoire when they are young, and these sorts of developmental constraints may limit their ability to make vocal adjustments later in life. 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. However, low frequency sounds tend to be masked when anthropogenic noise is present, and high frequency songs are more effective at eliciting female responses under these conditions. Birds may therefore experience competing selective pressures in habitats with high levels of anthropogenic noise: pressure to call more at lower frequencies in order to improve signal strength and secure good mates versus opposing pressure to sing at higher frequencies in order to ensure that calls are detected against a background of anthrophony. In addition, use of certain vocalizations, including high amplitude sounds that reduce masking in noisy environments, may impose energetic costs that reduce fitness. Anthropophony may ultimately have population- or community-level impacts on avian fauna. 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. In fact, nests in noisy habitats had higher survival than those laid in control habitats, presumably because noisy environments hosted fewer western scrub jays which are major nest predators of other birds. Thus, anthropophony can have negative effects on local species diversity, but the species capable of coping with noise disturbance may actually benefit from the exclusion of negative species interactions in those areas. Other experiments suggest that noise pollution has the potential to affect avian mating systems by altering the strength of pair bonds. When exposed to high amplitude environmental noise in a laboratory setting, zebra finches, a monogamous species, show a decreased preference for their mated partners. Similarly, male reed buntings in quiet environments are more likely to be part of a mated pair than males in noisy locations. == Anthropophony and insects ==

In comparison to other taxa, relatively little research has been done on the effects of anthropogenic noise on insects. However, current knowledge indicates that they are likely affected by anthropogenic noise to a greater extent than many other animal groups. Insects, like birds, rely heavily on acoustic signals for communication, which can be disrupted by noise. However, while birds and other taxa often studied for effects of anthropogenic noise primarily rely on airborne acoustic signals, insects frequently utilize vibrational signals for communication. The properties of vibrational signals increases the threat posed to them by anthropogenic noise. Furthermore, due to limited dispersal capacity and narrow habitat requirements, insects may be unable to avoid anthropogenic noise by moving to quieter locations. Similarly, noise that prevents insects from perceiving prey or potential dangers may result in decreased foraging success and survival. Mechanism of Impact 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. 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. and altering signal timing to take advantage of noise gaps. The efficacy of these responses varies depending on insects' ability to plastically modulate their behavior or signals, as well as the characteristics of the anthropogenic noise. Some insects can modulate the frequencies of their signals, shifting them higher or lower to avoid overlap with other noise. The ability of an insect species to modulate signals is constrained by physiological limits to the range of frequencies they are capable of producing. Additionally, numerous anthropogenic noises occupy a wide range of frequencies that may exceed the frequency range that insects can produce. Insects can also alter their behavior in response to noise by signaling within "gaps" of anthropogenic noise, during which there is less noise and less risk of being overlap. In environments when anthropogenic noise is constant, such as gas fields and wind farms, this behavioral modification likely is not a potential option for insects. 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. Even if insects can alter signaling behavior, they still might suffer reductions in fitness if females do not recognize the altered signals or respond to them as readily as non-altered signals. Under noisy conditions, females may also choose to mate with the first male encountered rather than sampling and comparing between males. Noise can also affect interactions among species. When noise masks airborne or vibrational signals made by prey, insects that rely on these cues to locate prey may be unable to, or prey species may alter their behavior to compensate for the noise. Ecological Impacts While there is little research on community or ecosystem level impacts of anthropogenic noise on insects, studies indicate that noise can decrease the diversity and abundance of insect communities. 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. ==Soundscape conservation==

The discipline of conservation biology has traditionally been concerned with the preservation of biodiversity and the habitats that organisms are dependent upon. However, soundscape ecology encourages biologists to consider natural soundscapes as resources worthy of conservation efforts. Soundscapes that come from relatively untrammeled habitats have value for wildlife as demonstrated by the numerous negative effects of anthropogenic noise on various species. In this situation, the (unintentional) senders of the acoustic signals will have no incentive to compensate for masking imposed by anthropogenic sound. 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. In the United States, the National Park Service's Natural Sounds and Night Skies Division is working to protect natural and cultural soundscapes. == See also ==