Habitat fragmentation increases habitat edge, which often enhances predation pressure. This phenomenon, termed the “edge effect,” has been documented for many organisms. However, its underlying mechanisms are not sufficiently understood, particularly for insect species. Thus, we aimed to interpret the behavioral mechanism of edge effects in two cicada species: Graptopsaltria nigrofuscata (Motschulsky) and Cryptotympana facialis (Walker) (Hemiptera: Cicadidae). In recent decades, the G. nigrofuscata has been decreasing in urban environments, whereas C. facialis has not. We compared the predation pressure by birds in four urban and three suburban habitats and we observed predation-avoidance behaviors. Results showed that the G. nigrofuscata incurred extremely high predation pressure. However, in C. facialis, predation pressure was constant among habitats. Behavioral observations revealed that predation avoidance of G. nigrofuscata was highly cover dependent, because threatened individuals hid in nearby trees. When tree cover is highly fragmented, the G. nigrofuscata probably has difficulty hiding. However, C. facialis fled cover independently. From these results, we concluded that the main causes of the decline of G. nigrofuscata in urban habitats were its cover dependence and the increasing discontinuity of tree coverage.
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Vol. 100 • No. 5