Effects of Woodland Shape on the Spatial Distribution and Density of 17-year Periodical Cicadas (Homoptera: Cicadidae)

Abstract

-We tested the hypothesis that the shape of woodland fragments influences the spatial distribution and density of three species of 17-year periodical cicadas (Homoptera: Cicadidae: Magicicada spp.). These characteristics were quantified for periodical cicadas emerging in four rectangular woodlots (mean size = 3.4 ? 0.7 ha), four linear wooded fencerows (>400 m long by mean width = 15.9 + 3.9 m), and the last remaining stand (81 ha) of primary beech-maple forest in southwestern Ohio, during the emergence of Brood X, May-June 1987. The shape of woodland fragments influenced spatial distribution and density of cicadas, although other factors, particularly the disturbance history of the sites, were equally important. Emergence began earlier in linear wooded fencerows and rectangular woodlot edges than in the interior of woodlots. Density of emerging individuals was greatest in the least disturbed edge areas and was low within the interior of rectangular woodlots. The relative abundances of the cicada species differed significantly between the woodland fragments and the primary forest. The smaller species, M. cassini (Fisher) and M. septendecula (Alexander and Moore), constituted over 93% of all individuals in all the linear and rectangular forest fragments, but the larger species, M. septendecim (L.), constituted 68% of individuals in the interior of the primary forest. We concluded that woodland shape influenced the spatial distribution of cicadas within the fragments, mainly due to the concentration of cicadas in edge areas. Our data also indicated that forest fragmentation shifted the relative abundances of these cicada species to the detriment of M. septendecim.