Avian predators are less abundant during periodical cicada emergences, but why?

Predation-driven geographical isolation of broods in periodical cicadas

Periodical cicadas are remarkable for their incredibly long, prime-numbered life cycles and almost perfectly synchronized mass emergence. Synchronized emergence is a generally localized event, referred to as a "brood". Broods are separated in space and time, or parapatric; adjacent broods emerge on different schedules, whereas some cicadas emerge off schedule, called stragglers. Straggling can potentially erode brood boundaries; thus, the mechanism allowing broods to maintain nonoverlapping distributions is highly puzzling. Here, we propose that predation may allow broods to exclude each other. Our model and numerical simulations show that predation could act as an important factor for maintaining the nonoverlapping distributions. The proposed mechanism is most effective in the vicinity of the critical strength of predation, beyond which the population is doomed to extinction. An increase in predation intensity increases resistance to settlement of a minority brood, while suppressing the main brood population.

The forest, the cicadas and the holey fluxes: Periodical cicada impacts on soil respiration depends on tree mycorrhizal type

The emergence of billions of periodical cicadas affects plant and animal communities profoundly, yet little is known about cicada impacts on soil carbon fluxes. We investigated the effects of Brood X cicadas (Magicicada septendecim, M. cassinii and M. septendeculain) on soil CO2 fluxes (RS ) in three Indiana forests. We hypothesized RS would be sensitive to emergence hole density, with the greatest effects occurring in soils with the lowest ambient fluxes. In support of our hypothesis, RS increased with increasing hole density and greater effects were observed near AM-associating trees (which expressed lower ambient fluxes) than near EcM-associating trees. Additionally, RS from emergence holes increased the temperature sensitivity (Q10 ) of RS by 13%, elevating the Q10 of ecosystem respiration. Brood X cicadas increased annual RS by ca. 2.5%, translating to an additional 717 Gg of CO2 across forested areas. As such, periodical cicadas can have substantial effects on soil processes and biogeochemistry.