Calling site preference reduces masking interference of acoustic signals among sympatric bush frogs and facilitates coexistence

Abstract

The degree of signal overlap among sympatric species strongly influences the efficiency of intraspecific communication. This phenomenon is particularly pronounced among species that rely heavily on acoustic communication for locating mates and defending territories. Signal interference presents the classic cocktail party problem and, hence, can pose challenges for these species as it can likely hinder the detection, recognition, and localisation of conspecifics. To overcome this challenge, sympatric species are expected to partition their acoustic space to minimise masking interference. We studied a group of sympatric and closely related endemic frogs in coffee plantations of the Western Ghats, India. This community is active for a limited period during the monsoon and, therefore, has a restricted breeding season. Acoustic communication during the breeding season is integral to these frog species, making them an ideal system to investigate possible strategies adopted by a community to minimise masking interference. Using observational data on the vertical height of calling sites and acoustics data, we show that the frog assemblage can partition in multidimensional trait axes, such as call frequency and space. In addition, a novel coexistence strategy emerges when combining these results, where frogs with similar acoustic parameters partition more in their space use. Our results broadly suggest that competition for acoustic space can drive signal and space-use partitioning and that vertical call site selection can enhance the minimisation of masking interference. Our study is among the few studies that test spatial stratification in conjunction with spectral stratification among coexisting species, and to the best of our knowledge, the first on amphibians.