Spatial heterogeneity of ambient sound at the habitat type level: ecological implications and applications

While spatial heterogeneity is one the most studied ecological concepts, few or no studies have dealt with the subject of ambient sound heterogeneity from an ecological perspective. Similarly to ambient light conditions, which have been shown to play a significant role in ecological speciation, we investigated the existence of ambient sound heterogeneity and its possible relation to habitat structure and specifically to habitat types (as syntaxonomically defined ecological units). Considering that the structure and composition of animal communities are habitat type specific and that acoustic signals produced by animals may be shaped by the habitat's vegetation structure, natural soundscapes are likely to be habitat specific. We recorded ambient sound in four forest and two grassland habitat types in Northern Greece. Using digital signal techniques and machine learning algorithms (self organizing maps, random forests), we concluded that ambient sound is not only spatially heterogeneous, but is also directly related to habitat type structure, pointing towards the existence of habitat type specific acoustic signatures. We provide evidence of the importance of soundscape heterogeneity and ambient sound signatures and a possible solution to the social cues versus vegetation characteristics debate in habitat selection theory.