Ecological Indicators (Sep 2024)
Acoustic indices track local vertebrate biodiversity in a subtropical landscape
Abstract
In the current biodiversity crisis, ecologists grapple with the formidable task of monitoring spatial and temporal trends in biodiversity. Ecoacoustics, or soundscape studies, leverage sound energy properties to characterize environmental aspects over time and space and are promising tools in the search for cost-effective methods for biodiversity monitoring. However, the potential of ecoacoustics can only be realized if ecoacoustic indices (EIs) summarizing the sound properties of ecosystems demonstrably and reliably reflect the biodiversity observed on the ground. In this study we assessed the correlation between seven widely used EIs and three survey-based indices of community diversity: species richness, Shannon’s diversity index and community composition. Utilizing standard field methods (censusing, trapping, etc.) for species richness and abundance, we surveyed local diversity of vertebrates at eight sites in a heterogeneous subtropical landscape while recording soundscapes at each site. We calculated community diversity indices from samples of bird, amphibian, reptile, and mammal guilds, and assessed how well different temporal aggregation of each EI correlated with known community diversity. We calculated seven EIs in addition to an index summarizing them and aggregated their values at five time frames (morning, evening, winter, spring, summer, and all recordings). Out of the 15 combinations arising from the exploration of the three community diversity dimensions for the four taxa and overall vertebrate diversity, 13 combinations presented significant correlations with at least one EI. Three indices, “Bioacoustics index”, “Acoustic Complexity’ and “Median of the amplitude envelope” correlated with aspects of biodiversity in all the analyzed groups, highlighting their value. Importantly, the time frame used for aggregating the indices influenced relationships across guilds and biodiversity aspects. We demonstrate that EIs aggregated at the appropriate time scale can accurately track various aspects of the diversity of local communities of vertebrates, supporting the use of EIs in biodiversity monitoring. However, we caution researchers and conservationists that detailed empirical assessments of the relation between diversity and soundscapes are still required across temporal and spatial scales to continue developing reliable acoustic indices that will accurately reflect the state of biodiversity.
