Toward a Synthetic Acoustic Ecology: Sonically Situated, Evolutionary Agent Based Models of the Acoustic Niche Hypothesis Alice Eldridge1;2 and Chris Kiefer1 1Emute Lab, Department of Music, University of Sussex, UK 2Peck Labs, Evolution, Behaviour & Environment, University of Sussex, UK [email protected] Downloaded from http://direct.mit.edu/isal/proceedings-pdf/alife2018/30/296/1904972/isal_a_00059.pdf by guest on 26 September 2021 Abstract creature choruses as more powerful, informative narratives in soundscape composition (Monacchi, 2013; Barclay and We introduce the idea of Synthetic Acoustic Ecology (SAC) as Gifford, 2018). However, there is a paucity of coherent the- a vehicle for transdisciplinary investigation to develop meth- ory addressing the ecological significance of global sound- ods and address open theoretical, applied and aesthetic ques- scapes, lack of effective computational tools for ecological tions in scientific and artistic disciplines of acoustic ecology. Ecoacoustics is an emerging science that investigates and in- monitoring (Sueur et al., 2008) and many latent creative terprets the ecological role of sound. It draws conceptually applications, for example in musical composition or game from, and is reinvigorating the related arts-humanities dis- world design. Just as Alife modelling has potential to medi- ciplines historically associated with acoustic ecology, which ate theoretical and empirical biology (Wheeler et al., 2002), are concerned with sonically-mediated relationships between we propose that a sonically situated flavour of Alife, which human beings and their environments. Both study the acous- tic environment, or soundscape, as the literal and concep- we call Synthetic Acoustic Ecology (SAC), may be a produc- tual site of interaction of human and non-human organisms. tive vehicle for investigation and a nexus of exchange be- However, no coherent theories exist to frame the ecological tween science, art and technological facets of acoustic ecol- role of the soundscape, or to elucidate the evolutionary pro- ogy in advancing our appreciation of soundscape as an inter- cesses through which it is structured. Similarly there is a lack face of human and natural systems which both reflects and of appropriate computational methods to analyse the macro soundscape which hampers application in conservation. We affects our coupled environments. propose that a sonically situated flavour of Alife evolutionary agent-based model could build a productive bridge between Soundscape, Ecoacoustics and Acoustic Ecology the art, science and technologies of acoustic ecological in- vestigations to the benefit of all. As a first step, two simple The term ‘soundscape’ has been used by a variety of disci- models of the acoustic niche hypothesis are presented which plines to describe the relationship between a landscape and are shown to exhibit emergence of complex spectro-temporal soundscape structures and adaptation to and recovery from the composition of its sound in both real and virtual worlds noise pollution events. We discuss the potential of SAC as a (Grimshaw and Schott, 2007). Originally coined in the con- lingua franca between empirical and theoretical ecoacoustics, text of urban design (Southworth, 1967) Soundscape was and wider transdisciplinary research in ecoacoustic ecology. later used by a group of environmentally-aware radio artists and sonic sociologists to describe ‘the acoustical characteris- tics of an area that reflect natural processes’ (Schafer, 1977). Introduction The scientific discipline of soundscape ecology recently pro- There is increasing interest across ecological science (Pi- posed a framework to investigate soundscape in terms of janowski et al., 2011; Sueur and Farina, 2015), arts (Bar- the causes and consequences of biological (biophony), geo- clay and Gifford, 2018; Monacchi and Krause, 2017; Mc- physical (geophony), and human-produced (anthrophony) Cormack et al., 2009) and humanities (Turner et al., 2003) sounds that emanate from a landscape (Pijanowski et al., in listening to, recording, investigating and interpreting the 2011). The emerging interdisciplinary science of Ecoa- acoustic environment - or soundscape - as the interface of coustics subsumes both soundscape ecology and bioacous- human and natural systems. If bioacoustics can be charac- tics (Sueur and Farina, 2015) to study the ecological role of terised as the study of the isolated duets of vocalising crit- sound. There is a growing impetus to develop acoustic ecol- ters, then the nascent field science of ecoacoustics is con- ogy as a truly interdisciplinary endeavour (Barclay and Gif- cerned with investigating and interpreting the ecological rel- ford, 2018), bridging traditional disciplinary divides. This is evance of the strains of full orchestra. A similar shift is ev- where we position Synthetic Acoustic Ecology. ident in the arts as representation in field recordings and Whereas bioacoustics infers behavioural information music has broadened from individual voices to collective from intra- and interspecific signals, ecoacoustics inves- tigates the ecological role of sound at higher ecological and evolutionary organisational units - from population and community up to landscape scales. Sound is understood as a core ecological component (resource) and ipso facto, due to structuring by competition, an indicator of ecological sta- tus (source of information). The field has been substantially bolstered by the increasing availability and decreasing costs of automated recording devices (Acevedo and Villanueva- Rivera, 2006; Farina et al., 2018), cheap storage and de- velopments in acoustic data processing (Truskinger et al., 2014). However, whilst it has drawn from theories of related ecological disciplines including bioacoustics, and landscape ecology (Turner et al., 2001), there is an absence of coher- ent theory regarding the ecological significance of the macro Downloaded from http://direct.mit.edu/isal/proceedings-pdf/alife2018/30/296/1904972/isal_a_00059.pdf by guest on 26 September 2021 soundscape. This not only constrains theoretical advances, but hampers potential applications such as environmental monitoring and prediction. Ecoacoustics is born of Bioa- coustic Big Data, but lacks coherent theories and computa- tional tools for effective development and application. Figure 1: Spectrogram (0 − 22:5 kHz) of a field record- Acoustic Niche Hypothesis ing made in the Ecuadorian amazon showing inter-taxon fre- Three hypotheses underpin ecoacoustics. The morphologi- quency partitioning of the acoustic environment. The vocal- cal adaptation hypothesis (MAH) and the acoustic adapta- isations of each taxa are bandlimited, minimising frequency tion hypothesis (AAH) are borrowed by bioacoustics and overlap between species; quasi temporal partitioning can describe how signals evolve through ecological feedback; also be observed in anuran species, although it is not clear the acoustic niche hypothesis is core to ecoacoustics (and here if this is conspecific or heterospecific. is also the hardest to evaluate) and describes the evolution of soundscape complexity. The MAH focuses on the ‘sender’ and hypothesises that the embodied form (body size, trachea less-disturbed habitats with unaltered species assemblages length, beak shape etc.) will shape potential range of signals will exhibit higher levels of coordination between inter- (Bennet-Clark, 1998). The AAH (Morton, 1975) predicts specific vocalizations than more heavily disturbed habitats, that acoustic properties of an environment can influence the where species assemblages are in rapid flux. Likewise, inva- evolution of vocalizations in certain species. sive species could create biophonic disturbances, thereby al- In his formulation of the ANH, musician-turned bioacous- tering natural acoustic partitioning (Pijanowski et al., 2011). tician Bernie Krause pointed out that both morphological This implies that if we listen in the right way we can hear and behavioural adaptations can also be triggered by inter- the health of an ecosystem. specific interference when organisms’ calls contain similar ANH is foundational to ecoacoustic theory and has ma- frequency and timing features (Krause, 1993). The ANH jor implications for ecological monitoring and prediction, was proposed after observation of complex arrangements of however empirical validation and development of applica- non-overlapping signals in recordings of soundscapes across tion is hard: firstly because it is not clear exactly what it multiple habitats. Krause postulated that this could be ex- means for a soundscape to exhibit ‘higher levels of coordina- plained by evolutionary pressure to minimize spectral or tion’; secondly because measurement of ecological integrity temporal overlaps in interspecific vocalizations. The ANH and even biodiversity remains contentious (Hillebrand et al., expands Hutchinson’s ecological niche concept (Hutchin- 2018); thirdly we lack appropriate computational meth- son, 1957) by adding a sonic dimension to evolutionary ods for community-level machine listening (Eldridge et al., ecospace. That vocalising species partition acoustic space 2016). Whilst research into bioacoustically motivated ma- to minimise interference from sympatric species has long chine listening algorithms for automated species detection is been recognised (Duellman and Pyles, 1983) in bioacous- well developed (e.g. Stowell and Plumbley (2014)), commu- tics. As illustrated in Figure 1, frequency partitioning across nity level indices