Established Barriers: Does fine-scale acoustic partitioning facilitate syntopy in two closely related Neotropical treefrogs?

Abstract The niche concept is a central paradigm in ecology, inspiring several ecological theories such as the acoustic niche hypothesis (ANH), which postulates that acoustic space is partitioned through temporal and spectral adjustments shaped by selection to reduce competition via masking interference among sympatric species. By measuring the acoustic overlap and sound signal discrimination between two closely related and syntopic treefrog species — Dendropsophus oliveirai and D. tapacurensis — we tested key predictions of the ANH, including partitioning and overlap in acoustic space. We combined traditional analyses of call stereotypy — descriptive statistics, coefficients of variation, analyses of variance — with acoustic space overlap metrics — kernel density estimation and fine-scale overlap — and Random Forest classification models. Despite an acoustic overlap that tended to increase with geographic distance from syntopic sites, significant differences between species occurred in most advertisement call parameters, particularly regarding spectral range and fine-scale pulse structure. Both species also displayed high within-species stereotypy in their signals. These findings indicates that reproductive isolation between the species is complete or in an advanced stage of differentiation driven by fine-scale acoustic adjustments. The patterns we uncovered illustrate general principles of the ANH, which are broadly relevant to understanding mechanisms of species coexistence in animal communities.