Temporal Soundscape Patterns in a Panamanian Tree Diversity Experiment: Polycultures Show an Increase in High Frequency Cover

Sandra Müller,Michael Scherer-Lorenzen,Catherine Potvin,Oliver Mitesser,Linda Oschwald

doi:10.3389/fevo.2022.808589

Abstract

In this ecoacoustic study we used the setting of a tropical tree diversity planted forest to analyze temporal patterns in the composition of soundscapes and to test the effects of tree species richness on associated biodiversity measured as acoustic diversity. The analysis of soundscapes offers easy, rapid and sustainable methods when assessing biodiversity. During the last years the quantification of regional or global acoustic variability in sounds and the analysis of different soundscapes has been evolving into an important tool for biodiversity conservation, especially since case studies confirmed a relationship between land-use management, forest structure and acoustic diversity. Here we analyzed soundscapes from two seasons (dry and rainy season) and aurally inspected a subset of audio recordings to describe temporal patterns in soundscape composition. Several acoustic indices were calculated and we performed a correlation analysis and a non-metric multidimensional scaling analysis to identify acoustic indices that: (i) were complementary to each other and such represented different aspects of the local soundscapes and (ii) related most strongly to differences in acoustic composition among tree species richness, season and day phase. Thus, we chose “High Frequency Cover,” “Bioacoustic Index,” and “Events Per Second” to test the hypothesis that acoustic diversity increases with increasing tree species richness. Monocultures differed significantly from polycultures during night recordings, with respect to High Frequency Cover. This index covers sounds above 8 kHz and thus represents part of the orthopteran community. We conclude that increasing tree species richness in a young tropical forest plantation had positive effects on the vocalizing communities. The strongest effects were found for acoustic activity of the orthopteran community. In contrast to birds, orthopterans have smaller home ranges, and are therefore important indicator species for small scale environmental conditions.

Highlights

Habitat loss, agricultural activities, global warming and the introduction of exotic species lead to massive decreases of biodiversity all over the world (Sala et al, 2000; Cardinale et al, 2012; IPBES, 2019b)
Since acoustic community composition and dynamics vary among different biomes in interaction with local geophony and anthropophony, it may be necessary for each ecoacoustic study to identify its own unique set of indices to describe soundscape composition
In this study we showed that planting polycultures increased orthopteran acoustic activity at night, and this may be related to an increase in abundance and maybe richness of this taxonomic group

Summary

Introduction

Agricultural activities, global warming and the introduction of exotic species lead to massive decreases of biodiversity all over the world (Sala et al, 2000; Cardinale et al, 2012; IPBES, 2019b). With habitat loss being a major driver of species loss and deforestation still increasing dramatically in the tropics (Brooks et al, 2002; IPBES, 2019a), afforestation is an important and widely used tool for restoring ecosystems and mitigating climate change. Monocultures are likely less suited than natural secondary forests or mixed-species plantations for promoting and restoring associated biodiversity (Perfecto et al, 1997; Ampoorter et al, 2020). Increasing tree species richness in plantations might have multiple consequences for the associated fauna, by providing a broader range of food sources for both generalists and specialists herbivores, which could scale up to higher trophic levels (Brose, 2003; Potts et al, 2003; Castagneyrol and Jactel, 2012; Pekin et al, 2012; Ebeling et al, 2018). Changes in tree species richness has consequences for microclimatic conditions that could affect both diversity and abundance of the animal communities as well as temporal activity patterns (Walker, 1975a,b; Akutsu et al, 2007; Checa et al, 2014; Kunz et al, 2019; Campos-Cerqueira et al, 2020; Burivalova et al, 2021)

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