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 choruses, competition for acoustic space is expected to drive signal differentiation among heterospecific signals. The acoustic space partitioning hypothesis proposes that species differentiate their signals to reduce overlap and thereby reduce 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 co-signaling, limited acoustic space, and signal masking at the receiver. Without explicit evidence of conditions for acoustic interference, signal differentiation alone is insufficient to infer that competition is driving partitioning, since this outcome may also arise from alternative processes. By integrating 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 choruses.