Acoustic indices as proxies for biodiversity: a meta-analysis

As biodiversity decreases worldwide, the development of effective techniques to track changes in ecological communities becomes an urgent challenge. Together with other emerging methods in ecology, acoustic indices are increasingly being used as novel tools for rapid biodiversity assessment. These indices are based on mathematical formulae that summarise the acoustic features of audio samples, with the aim of extracting meaningful ecological information from soundscapes. However, the application of this automated method has revealed conflicting results across the literature, with conceptual and empirical controversies regarding its primary assumption: a correlation between acoustic and biological diversity. After more than a decade of research, we still lack a statistically informed synthesis of the power of acoustic indices that elucidates whether they effectively function as proxies for biological diversity. Here, we reviewed studies testing the relationship between diversity metrics (species abundance, species richness, species diversity, abundance of sounds, and diversity of sounds) and the 11 most commonly used acoustic indices. From 34 studies, we extracted 364 effect sizes that quantified the magnitude of the direct link between acoustic and biological estimates and conducted a meta-analysis. Overall, acoustic indices had a moderate positive relationship with the diversity metrics (r = 0.33, CI [0.23, 0.43]), and showed an inconsistent performance, with highly variable effect sizes both within and among studies. Over time, studies have been increasingly disregarding the validation of the acoustic estimates and those examining this link have been progressively reporting smaller effect sizes. Some of the studied indices [acoustic entropy index (H), normalised difference soundscape index (NDSI), and acoustic complexity index (ACI)] performed better in retrieving biological information, with abundance of sounds (number of sounds from identified or unidentified species) being the best estimated diversity facet of local communities. We found no effect of the type of monitored environment (terrestrial versus aquatic) and the procedure for extracting biological information (acoustic versus non-acoustic) on the performance of acoustic indices, suggesting certain potential to generalise their application across research contexts. We also identified common statistical issues and knowledge gaps that remain to be addressed in future research, such as a high rate of pseudoreplication and multiple unexplored combinations of metrics, taxa, and regions. Our findings confirm the limitations of acoustic indices to efficiently quantify alpha biodiversity and highlight that caution is necessary when using them as surrogates of diversity metrics, especially if employed as single predictors. Although these tools are able partially to capture changes in diversity metrics, endorsing to some extent the rationale behind acoustic indices and suggesting them as promising bases for future developments, they are far from being direct proxies for biodiversity. To guide more efficient use and future research, we review their principal theoretical and practical shortcomings, as well as prospects and challenges of acoustic indices in biodiversity assessment. Altogether, we provide the first comprehensive and statistically based overview on the relation between acoustic indices and biodiversity and pave the way for a more standardised and informed application for biodiversity monitoringThis study was supported by a research project funded by the Comunidad de Madrid and the European Social Fund (PEJ2018-AI/AMB-9957, to D. L.). We thank Camille Desjonquères for her valuable comments on the study design, Alison Cooper for her exhaustive and insightful revision of the manuscript, and anonymous reviewers for their significant contribution. I. A. and L. S. M. S. acknowledge research grants provided by the Comunidad de Madrid (PEJ-2018-AI/ AMB-9957, to D. L.) and the Ministerio de Economía, Industria y Competitividad of Spain (PEJ-2018-004603-A, to D. L.), respectively, together with the support of the European Social Fund. H. L. was supported by the FPI program of the Ministerio de Ciencia e Innovacion of Spain (grant CGL2017-86926-P). D. L. also acknowledges a postdoctoral grant provided by the Comunidad de Madrid (2020-T1/AMB-20636, Atraccion de Talento Investigador, Spain) and a research project funded by the Ministerio de Economía, Industria y Competitividad (CGL2017-88764-R, MINECO/AEI/FEDER, Spain

Olive grove intensification negatively affects wintering bird communities in central Spain

Agricultural intensification is a persistent and growing threat to biodiversity worldwide. Olive groves cover extensive areas in the Mediterranean basin and play a fundamental role as refuge and wintering quarters for many bird species, but the effects of their current intensification on bird communities remain unclear. This study aims to evaluate the response of wintering birds to the management of olive groves with different degrees of intensification (traditional, intensive and super-intensive management) in central Spain. Based on two bird censuses conducted in 25 groves in early and late winter, we examined the influence of habitat structure and composition at different spatial scales on species richness and abundance of the entire farmland bird community, and of the diet-based functional groups. Total species richness tended to decrease with intensive olive grove management, probably due to reduced habitat heterogeneity, whereas total abundance did not, indicating the capacity of intensive and super-intensive olive groves to sustain large numbers of wintering birds. The negative effect of intensification was particularly evident in frugivore species richness, while frugivore abundance was positively (but marginally) associated with olive fruit availability. Granivorous species were positively associated with lower vegetation cover, but insectivorous species did not respond to intensification gradients. Species richness and abundance (total and by diet-based functional groups) also decreased from early to late winter, which may be due to the effect of olive harvest, but also to an extreme cold event. Overall, our findings show how olive grove intensification and the associated management practices result in significant changes in habitat structure and composition at different spatial scales, thus affecting wintering bird communitiesWe thank the Faculty of Sciences from Universidad Autónoma de Madrid for their financial support through their TFM support line. D.L. acknowledges a postdoctoral grant provided by the Comunidad de Madrid (2020-T1/ AMB-20636, Atraccion de Talento Investigador, Spain). This paper is a contribution to REMEDINAL-TE project (P2018/EMT-4338; Madrid Regional Government and EU Social Fund

Aplicación de la bioacústica al seguimiento de anfibios

Ministerio de Ciencia e Innovación del Gobierno de España TEMPURA: CGL2005-00092/BOS y ACOURA: CGL2008-04814-C02Ministerio de Economía y Competitividad del Gobierno de España. TATANKA: CGL2001/2506

Acoustic species distribution models (aSDMs): A framework to forecast shifts in calling behaviour under climate change

Species distribution models (SDMs) are a key tool for biogeography and climate change research, although current approaches have some significant drawbacks. The use of species occurrence constrains predictions of correlative models, while there is a general lack of eco-physiological data to develop mechanistic models. Passive acoustic monitoring is an emerging technique in ecology that may help to overcome these limitations. By remotely tracking animal behaviour across species geographical ranges, researchers can estimate the climatic breadth of species activity and provide a baseline for refined predictive models. However, such integrative approach still remains to be developed. Here, we propose the following: (a) a general and transferable method to build acoustic SDMs, a novel tool combining acoustic and biogeographical information, (b) a detailed comparison with standard correlative and mechanistic models, (c) a step-by-step guide to develop aSDMs and (d) a study case to assess their effectiveness and illustrate model outputs, using a year-round monitoring of calling behaviour of the Iberian tree frog at the thermal extremes of its distribution range. This method aims at forecasting changes in environmental suitability for acoustic communication, a key and climate-dependent behaviour for a wide variety of animal taxa. aSDMs identified strong associations between calling behaviour and local environmental conditions and showed robust and consistent predictive performance using two alternative models (regression and boundary). Furthermore, these models better captured climatic variation than correlative models as they use observations at higher temporal resolution. These results support aSDMs as efficient tools to model calling behaviour under future climate scenarios. The proposed approach offers a promising basis to explore the capacity of vocal species to deal with climate change, supported by an innovative integration of two disciplines: bioacoustics and biogeography. aSMDs are grounded on ecologically realistic conditions and provide spatially and temporally explicit predictions on calling behaviour, with direct implications in reproduction and survival. This enables to precisely forecast shifts in breeding phenology, geographic distribution or species persistence. Our study demonstrates how acoustic monitoring may represent an increasingly valuable tool for climate change researchConsejería de Educación e Investigación, Grant/Award Number: 2020-T1/AMB20636 and 2017-T2/AMB-6035; European Commission, Grant/Award Number: EAVESTROP-661408; Ministerio de Economía, Industria y Competitividad, Grant/Award Number: CGL2017-88764-

Anurans, the Group of Terrestrial Vertebrates Most Vulnerable to Climate Change: A Case Study with Acoustic Monitoring in the Iberian Peninsula

We report preliminary analyses from an ongoing sound monitoring project that involves five species of anurans: two species of tree frogs in the genus Hyla (Hylidae) and three species of midwife toads in the genus Alytes (Discoglossidae) in the Iberian Peninsula. Each station was monitored with an automated recording system based on solid state recorders, coupled with programmable temperature and relative humidity probes. We present comparative data of vocal activity of two populations of Alytes cisternasii from thermal extremes of the species range using human detection and commercial automated sound recognition software. Parameters such as duration of reproductive season, preferred temperatures for calling activity and relation with relative humidity are discussed. We compare the performance of analysing the recordings between an automated system of detecting the presence of Alytes cisternasii calls and listening of the recordings by non-expert personnel.Ministerio de Educación y Ciencia de España. Proyecto "Tempura

The Amphibian Research in Sierra Norte Natural Park, sw. Spain

A nivel mundial, los anfibios están desapareciendo por causas muy diversas, algunas poco conocidas, como los efectos del cambio climático. Son, en general, especies muy sensibles a los cambios en el medio y, por tanto, resultan especialmente interesantes tanto para los investigadores como para todo aquel interesado en la conservación de la biodiversidad. Desde hace años, investigadores del CSIC y otros centros españoles (Universidad de Sevilla y Granada) y extranjeros (Universidad de Lisboa, Portugal, Universidad de Chile y la Universidad de Western Kentucky, USA) están realizando estudios sobre bioacústica, biología de la reproducción, variación geográfi ca y adaptaciones locales, morfología y dinámica poblacional de algunas especies presentes en el Parque Natural de la Sierra Norte. Los resultados más relevantes de tales estudios se resumen en estas páginas, incluyendo resultados preliminares de un proyecto nacional I+D+i, actualmente en marcha. Además, sus observaciones han permitido detectar y sugerir acciones que están permitiendo mejorar la conservación de algunas de estas poblaciones. Con ello esperamos contribuir a un mejor conocimiento y conservación de estas especies y su medio.Currently, there is a global decline of amphibians due to an array of different factors, including global warming. Amphibians are among the more sensitive vertebrate species to changes in the environment, what target them both for research and for anyone interested in biodiversity conservation. During the last decade, researchers from diff erent institutions, including CSIC, the University of Seville, the University of Granada, the University of Lisbon, the University of Chile, and Western Kentucky University, have conducted studies on population divergence and local adaptations, bioacoustics, reproductive biology, morphology, and population dynamics of some of the anuran species occurring in the Natural Park of Sierra Norte. In this paper, we summarize relevant results from these studies, including preliminary results from an ongoing I+D+i national project. These studies have already help us to detect and suggest some conservation actions for amphibians, which once implemented, will improve the conservation status of some of these amphibian populations. Our hope is to contribute to increase the knowledge and conservation of these species and their habitats