Japanese biologists* noted a change in the composition of cicada species in Osaka, Japan. In the 1980s and 90s, many of the previously dominant cicada species declined and were replaced by a single dominant species, Cryptotympana facials. What caused this change in species composition?
A number of environmental variables were studied. One variable, soil hardness, was best correlated with observations. In urban areas, soil is subjected to a variety of activities that increase soil compaction. Human traffic, vehicle traffic, and tillage practices all leave the soil more compacted. Thus, urban soils are more compacted and harder. For burrowing insects such as cicada immatures, hard compacted soils can exclude species. Experiments show that Cryptotympana facialis is capable of burrowing in more compacted, harder soils compared to other species. The loss of species can be explained by changes in soil compaction. Cryptotympana facialis, freed from competition with other species has become dominant.
*Minoru Moriyama and Hideharu Numata. Urban soil compaction reduces cicada diversity. Zoological Letters (2015) 1:19