Amazonian soundscapes: unravelling the secrets of insect acoustic niches in diverse habitats

Insects are the most diverse animal taxon on Earth and play a key role in ecosystem functioning. However, they are often neglected from biodiversity surveys due to the difficulties of monitoring this small and hyper-diverse taxon. With technological advancements in biomonitoring and analytical methods, these shortcomings may finally be addressed. Here, we performed passive acoustic monitoring at 141 sites (eight habitats) in the Amazon to advance insect surveys using acoustic methods. We first describe the frequency range occupied by three soniferous insect groups (cicadas, crickets, and katydids) to calculate the Acoustic Evenness Index (AEI). Then, we assess the temporal and spatial variations of AEI among the insect categories, and finally we investigate the relationship among vegetation structure variables and AEI for each category. Overall, crickets occupied lower and narrower frequency bands than cicadas and katydids. AEI values varied among insect categories and across space and time. There was higher acoustic activity before sunrise and lower acoustic activity was recorded at pastures. Canopy cover was positively associated with crickets' acoustic activity but not with katydids. Our findings contribute to a better understanding of the role of time, habitat, and vegetation structure in shaping insect activity within the diverse Amazonian ecosystem.