Relocation and Concentration in the 2004 Emergence of Periodical Cicadas

Indiana University, Bloomington IN

Investigators

Abstract

Emergences of periodical cicadas are spectacular events and may exert important effects on forest ecology. This project is an investigation of the general hypothesis that human modifications of forest environments increase the effects of cicada emergences by causing cicadas to concentrate in particular environments. Periodical cicadas spend most of their lives underground but adults emerge to reproduce, at 13 or 17-year intervals, and their spatial behavior during the brief emergence period accounts for the relocation and concentration of cicada populations. The large biomass of cicadas produces a major flux of nutrients from below to above ground. Emerging cicadas also inflict substantial damage on trees and shrubs as they deposit eggs in twigs and the emergence ends a period of heavy feeding on tree roots by maturing nymphs and initiates a period of lighter feeding by younger nymphs of the next generation. These effects may alter ecological dynamics by favoring some species of trees and shrubs but the effects will depend on the spatial concentration of cicadas. That concentration is likely to be altered by human modification of the forest, since cicadas select areas of forest edge and recent disturbance to deposit the eggs that produce the next generation. The largest brood of periodical cicadas will emerge in Spring, 2004 and the analysis will be based on spatial samples that will be sufficient to analyze the location of the cicada population before and after the emergence. The samples will be used to test specific hypotheses about the net relocation and concentration of the cicada population using methods for spatial statistical analysis. The project will reveal specific features of the ways that human activity works in conjunction with a natural process, specifically the spatial behavior of cicadas, to alter ecological dynamics and modify a forest environment.