A synthesis of the evidence for the acoustic space partitioning hypothesis

Acoustic interference is a critical factor driving the evolution of communication systems. In mixed-species aggregations, competition for acoustic space is expected to drive signal differentiation among heterospecifics. The acoustic space partitioning hypothesis proposes that species differentiate their signals to reduce overlap and thereby acoustic interference. Despite ongoing debates in niche theory, studies in animal communication have remained disconnected from these conversations, and no critical evaluation of this hypothesis has been conducted. We performed a systematic review to assess empirical support for acoustic space partitioning and evaluate the conceptual and methodological approaches used to test it. We found that two-thirds of studies conclude that the acoustic space is partitioned, albeit with a strong taxonomic bias toward anurans. However, studies rarely account for key assumptions of the hypothesis, including cosignaling, limited acoustic space, and masking of the signal at the receiver. Without explicit evidence of conditions for acoustic interference, signal differentiation alone is insufficient to infer competition as the main mechanism driving partitioning, since this outcome may also arise from alternative processes. By integrating coexistence theory and sensory ecology, we provide a framework to reconcile signal-structure differentiation with receiver perception, thereby improving our understanding of how communication systems evolve in mixed-species aggregations.