concepts

This is brief introduction to ecoacoustics. Please refer to the publication cited below for more information or visit the site of the International Society of Ecoacoustics.

definition

Ecoacoustics is a recent scientific discipline that was born at the occasion of a congress we organised with the University of Urbino in 2014 at the Muséum national d’Histoire naturelle. We then defined ecoacoustics as « a theoretical and applied discipline that studies sound along a broad range of spatial and temporal scales in order to tackle biodiversity and other ecological questions. The use of sound as a material from which to infer ecological information enables ecoacoustics to investigate the ecology populations, communities and landscapes » (Sueur & Farina, 2015).

Group picture at the International Society of Ecoacoustics first meeting in 2014 in Paris.

Ecoacoustics differ from bioacoustics in several aspects. First of all the sound produced by animals is not studied as a behavioural act – a sexual display or a mother-pup recognition system – but as an ecological cue. Basically, ecoacoustics eavesdrops on animal sound to track biodiversity or to consider ecological questions potentially in link with biological conservation.

Ecoacoustics works at several ecological organization levels, mainly at the population, community, ecosystem and landscape levels The species and habitat concepts are relevant can be evoked at each study level. Ecoacoustics aims at analysing the sound coming from nature over the long term and over large space scales.

organization_scales
Ecoacoustics studies the sound coming from animals at large-scales (black) when bioacoustics mainly focuses on the individual scale (grey). J.Sueur

At the landscape level, the soundscape is usually divided into three main components, as defined by Bernie Krause: the biophony (biotic sounds as the a bird or a whale song), the geophony (abiotic sounds as the sound a running water), and the anthropophony (human sounds).

The three main components of a soundscape, following Bernie Krause defintion.

Ecoacoustics differs from bioacoustics but they reinforce mutually, behaviour data being helpful to understand ecological processes and ecology data being able to explain certain behavioural acts.

theories

Ecoacoustics mainly refers to two evolutionary theories: the acoustic niche hypothesis (ANH) and the acoustic adaptation hypothesis (AAH).

The ANH is due to Bernie Krause in 1993. The hypothesis is based on Hutchinson niche theory applied to sound. Each species is supposed to occupy a specific acoustic niche in the acoustic environment so that interferences between species are minimized. The ANH should lead to a divergence between species and therefore to a partitioning of the acoustic space.

The AAH was introduced by Eugene Morton in 1975. This theory stipulates that animal vocalizations should be adapted to the environment they travel through. Natural and sexual selection would operate so that signal propagation is maximized. Because several species share the same habitat they should show shared parameters in their sounds. The AAH should then lead to a convergence between species and therefore to an habitat signature.

The AAH should lead to a convergence of the sounds produced by species found in the same habitat (left) when the ANH should lead to a divergence of the same sounds. J. Sueur

Both hypotheses therefore operate in opposite evolutionary directions. The main issue is that they are often considered separately when they probably concur.

tools

The working flow of ecoacoustics can be summarized as follow:
hypothesis → sampling design → automatic recording → data storage → signal analysis → data analysis → visualization → statistics → interpretation → conclusion

We work on each step of this workflow but we focus on developing techniques related to signal analysis and data analysis. In particular we develop acoustic indices that aim at estimating the acoustic diversity found in a recording (α indices) and at comparing recordings achieved at different times and/or different places (β indices). We also use or develop techniques to classify sounds of interest (supervised machine learning) or to cluster similar sounds (unsupervised machine learning). These tools mainly aims at estimating the richness (number of acoustic items) and composition (relative abundance of acoustic items) in a recording.

conservation

The challenge in conservation is two fold: acoustic conservation and biological conservation. The conservation of the recordings in an appropriate library is a priority for science repeatability, data sharing, and citizen legacy. Also convinced that biodiversity needs to be described and monitored to be preserved we wish to develop research that can be applied by decision makers and stakeholders to improve nature conservation.

publications

. Sueur J, Krause B, Farina A (2019) – Climate change is breaking Earth’s beat. Trends in Ecology and Evolution, in press. link
. Sueur J, Farina A (2015) – Ecoacoustics: the ecological investigation and interpretation of environmental sound. Biosemiotics, 8: 493-502. link
. Gasc A, Pavoine S, Lellouch L, Grandcolas P, Sueur J (2015) – Acoustic indices for biodiversity assessments: analyses of bias based on simulated bird assemblages and recommendations for field surveys. Biological Conservation, 191: 306-312. link
. Sueur J, Farina A, Gasc A, Pieretti N, Pavoine S (2014) – Acoustic indices for biodiversity assessment and landscape investigation. Acta Acustica united with Acustica, 100: 772-781. link
. Lellouch L, Pavoine S, Jiguet F, Glotin H, Sueur J (2014) – Monitoring temporal change of bird communities with dissimilarity acoustic indices. Methods in Ecology and Evolution, 4: 495-505. link
. Towsey M, Parsons S, Sueur J (2014) – Ecology and acoustics at a large scale. Ecological Informatics, 21: 1-3. link
. Gasc A, Sueur J, Jiguet F, Devictor V, Grandcolas P, Burrow C, Depraetere M Pavoine S (2013) – Assessing biodiversity with sound: do acoustic diversity indices reflect phylogenetic and functional diversities of bird communities? Ecological Indicators, 25: 279-287. link

video

A conference shared with Hervé Glotin (Université de Toulon) about ecoacoustics. In French