Integrating the concept of acoustic diversity into the functional ecology framework

The ecological relevance of sounds in ecosystems has gained increasing attention in the recent decade. While ecoacoustics seeks to study these roles, a majority of studies to date have focused on using Passive Acoustic Monitoring (PAM) for species monitoring or calculating integrative ecoacoustic indices as rapid proxies for biological diversity. This paper proposes an ecological perspective on acoustic diversity that distinguishes three core interconnected dimensions: (i) compositional acoustic diversity, reflecting the acoustic assemblage present; (ii) structural acoustic diversity, describing the spatial and temporal organisation of acoustic activity; and (iii) functional acoustic diversity, relating to variation in acoustic traits involved in information exchange. We aim to provide a clearer conceptualisation of what different approaches to acoustic diversity represent ecologically and how they can be related to biodiversity and ecosystem functioning. We present a conceptual framework for acoustic diversity, building on existing research and linking it to Noss's (1990) hierarchical classification of biodiversity. We define and distinguish compositional, structural, and functional acoustic diversity across spatial scales ranging from the individual to the soundscape, and consider variation in alpha, beta, and gamma diversity within these dimensions. We propose methods for quantifying these different aspects of acoustic diversity and provide application examples and exemplary hypotheses to illustrate how the framework could be operationalised.