Many scientists have expressed a need for a new scalable approach to monitoring biodiversity that takes advantage of recent advances in technology, which could allow us to quickly identify and respond to ecological changes. Monitoring biodiversity through the use of remotely recorded sound is one method that has been proposed to fulfill these requirements.
The objective of this study is to develop an index (the Modified Acoustic Entropy Index (H’)), using remotely recorded sound, to examine variations in acoustic entropy in agricultural soundscapes, and to test the ability of this index to indicate relative biodiversity levels in these systems. To do this, the H’ index examines the level of niche utilization of the acoustic soundscape, which is hypothesized to relate to the number of species and individuals present in a location. The resulting H’ values can then be used to compare soundscape patterns and acoustic diversity levels over time and between locations.
Six locations with divergent Agricultural Health Index (AHI) levels, were selected to test the H’ index. Analyses were conducted to address five key questions: (1) Is there a significant relationship between the acoustic entropy (H’) of sites and their agroecosystem health index values, and/or the AHI’s component variables (Plant landscape diversity (BD), soil quality (SOIL), topography (ELV), social organization (SOC), farm economics (CAUV), and land economics (MKT)); (2) Are H’ levels comparable to those found using traditional measures of biodiversity (plant transect, insect pitfall, and avian call number); (3) How does the sampling radius of H’ compare to the sampling radius of traditional methods; (4) What is the length of sampling needed to ensure significant power of analysis; and (5) can the H’ index be used to identify and analyze anthropogenic disturbances.
The results of this study indicate that (1) during certain time periods the H’ index is significantly related to the Agricultural Health Index, plant heterogeneity, and soil quality; (2) In contrast, the standard methods were not related to the biodiversity measure, Plant heterogeneity. Furthermore, none of the traditional methods tested were correlated with each other, calling into question their usefulness as a surrogate for total diversity; (3) Additionally, the sampling radius of the H’ index (> 1,000 m) was found to be greater than that of the traditional methods; (4) For six sites, a sampling period of greater than seven weeks is recommended. Because the index is calculated over a longer period of time, however, it can be used to discern diel and seasonal patterns of animal activity, which cannot be detected as easily using more traditional methods; (5) While the H’ index could be used to identify anthropogenic acoustic disturbances, no difference in rebound time between sites was detected.
Therefore, although the H’ index was not correlated with any of the traditional methods, the consistency of the patterns seen and the agreement of the H’ with the AHI tentatively suggest that the H’ index may be used to detect significant differences in diversity as or more consistently than traditional methods of biodiversity assessment