Spectral overlap and temporal avoidance in a tropical savannah frog community

Abstract

Vocalizing animals often occur in complex acoustic environments where there is a high chance of acoustic interference from co-occurring species with spectrally overlapping vocalizations. Acoustic interference impedes detection and discrimination of signals, and may ultimately reduce fitness. The aim of this study was to determine the relationship between spectral overlap and temporal overlap in a tropical savannah frog community. We predicted that species pairs that overlap spectrally would behaviourally respond to one another by avoiding calling at the same time, to minimize acoustic interference. We determined the calling activity of 14 frog species at four locations across 4 months during peak breeding season. We then determined the difference between observed and expected temporal overlap for all species pairs as a function of spectral overlap at three temporal scales (night-minute-call). There was potential for acoustic interference between many of the species studied with the calls of up to half of the species pairs at each site overlapping spectrally. There was no relationship between spectral overlap and observed–expected temporal overlap at either the night or minute level. Instead, calling activity was aggregated at both the night and minute level. Evidence of a negative relationship between spectral overlap and temporal overlap was found at the call level, with species pairs with greater mean spectral overlap calling together less frequently than expected. The observed aggregated calling at the night and minute level suggest that at gross timescales, factors other than avoiding spectral overlap are driving calling activity in tropical savannah frog communities. The call level avoidance found in this study may be sufficient for spectrally overlapping species pairs to avoid the negative effects of acoustic interference, allowing them to call during the same nights and at similar times to take advantage of favourable environmental conditions.