Luypaert, T. | bioRxiv Science

bioRxiv2023

Extending species-area relationships into the realm of ecoacoustics: The soundscape-area relationship

The rise in species richness with area is one of the best-studied patterns in ecology. Yet, little is known about the spatial scaling of alternate dimensions of diversity. Here, we provide empirical evidence for a relationship between the richness of acoustic traits emanating from the landscape, or soundscape richness, and the island area, which we term the Soundscape Area Relationship (SSAR). We show a positive relationship between the gamma soundscape richness and island area, with slope and R2-values of comparable magnitude to those reported in the literature. This relationship breaks down at the smallest spatial scales, indicating a small-island effect. Moreover, we demonstrate a positive spatial scaling of the plot-scale alpha soundscape richness, but not the beta soundscape turnover, suggesting disproportionate effects are an important underlying mechanism. We conclude that the scaling of biodiversity can be extended to the realm of ecoacoustics, implying soundscape metrics are sensitive to fundamental ecological patterns and useful to disentangle the complex mechanisms that drive them.

ecology↗

bioRxiv2022

A framework for the quantification of soundscape diversity using Hill numbers

O_LISoundscape studies are increasingly common to capture landscape-scale ecological patterns. Yet, several aspects of soundscape diversity quantification remain unexplored. Although some processes influencing acoustic niche usage may operate in the 24h domain, most acoustic indices only capture the diversity of sounds co-occurring in sound files at a specific time of day. Moreover, many indices do not consider the relationship between the spectral and temporal traits of sounds simultaneously. To provide novel insights into landscape-scale patterns of acoustic niche usage at broader temporal scales, we present a workflow to quantify soundscape diversity through the lens of functional ecology. C_LIO_LIOur workflow quantifies the functional diversity of sound in the 24-hour acoustic trait space. We put forward an entity, the Operational Sound Unit (OSU), which groups sounds by their shared functional properties. Using OSUs as our unit of diversity measurement, and building on the framework of Hill numbers, we propose three metrics that capture different aspects of acoustic trait space usage: (i) soundscape richness; (ii) soundscape diversity; (iii) soundscape evenness. We demonstrate the use of these metrics by (a) simulating soundscapes to assess if the indices possess a set of desirable behaviours; and (b) quantifying the soundscape richness and evenness along a gradient in species richness to illustrate how these metrics can be used to shed unique insights into patterns of acoustic niche usage. C_LIO_LIWe demonstrate that: (a) the indices outlined herein have desirable behaviours; and (b) the soundscape richness and evenness are positively correlated with the richness of soniferous species. This suggests that the acoustic niche space is more filled where taxonomic richness is higher. Moreover, species-poor acoustic communities have a higher proportion of rare sounds and use the acoustic space less effectively. As the correlation between the soundscape and taxonomic richness is strong (>0.8) and holds at low sampling intensities, soundscape richness could serve as a proxy for taxonomic richness. C_LIO_LIQuantifying the soundscape diversity through the lens of functional ecology using the analytical framework of Hill numbers generates novel insights into acoustic niche usage at a landscape scale and provides a useful proxy for taxonomic richness measurement. C_LI

ecology↗