The acoustic niche hypothesis meets habitat fragmentation and isolation

Research Highlight: Han P, Yang Y, Kajanus MH, Lu W, Chen Q, Ding P, Si X. (2025). Community composition coupled with habitat fragmentation drives acoustic divergence in bird assemblages. Journal of Animal Ecology doi: 10.1111/1365-2656.70185. Animals that communicate acoustically have to deal with the problem of getting their message through environments often crowded by acoustic signals from other individuals (from the same and different species). This poses the problem that the signal of interest may be masked by these other sounds, lowering the probability that it will be detected/discriminated by targeted receivers. The acoustic niche hypothesis (ANH; Krause 1993) predicts that acoustic signals will occupy different acoustic niches (e.g. different frequencies, Hz) to lower competition for the acoustic space. Han et al. (2025) put this idea to the test. While various studies have tested the acoustic niche hypothesis in relation to biotic factors (e.g. species richness and abundance), Han et al. (2025) went one step further by also considering habitat fragmentation and isolation. To do so, they recorded the songs of 51 bird species in 12 islands differing in size (as a measure of habitat fragmentation) and distance to nearest island and mainland (as a measure of isolation). Han et al. (2025) also took into account body mass and evolutionary history. As expected, they found that biotic factors (body mass and species richness) and phylogenetic relationships were associated with the degree of competition and acoustic partitioning. Interestingly, the authors also found that island size and isolation played an important role (acoustic partitioning increased in more isolated islands and in smaller islands). These results confirm the ANH and provide evidence that habitat fragmentation and isolation can also play a role influencing acoustic partitioning in birds.