Ecotope Characteristics of Coexisting Erythroneura Leafhoppers (Homoptera; Cicadellidae) on Sycamore

Abstract

Eight species of leafhoppers (Homoptera: Cicadellidae) of the genus Erythroneura (maculata group) breed on the American sycamore, Platanus occidentalis L. Several occur sympatrically in many areas throughout the range of their host plant even though they have been shown to compete severely for the last 9 weeks of the season in Illinois. The species are E. arta Beamer, E. bella McAtee, E. hymettana Knull, E. ingrata Beamer, E. lawsoni Robinson, E. morgani (DeLong), E. torella Robinson, and E. Usitata Beamer. Five of these are sibling species. Ecotope characteristics (niche and habitat) were examined to determine the factors which permit coexistence in this leafhopper guild on sycamore. The five niche or intracommunity factors examined were temporal utilization, distribution within the canopy, occurrence on leaves of various sizes and ages, and location of feeding sites on the leaf. There were insufficient differences between species for all five niche parameters to explain coexistence in the guild by niche segregation. Three habitat or intercommunity parameters were examined: occurrence on trees alone a moisture gradient, latitudinal distribution with respect to that of sycamore, and distribution within a given geographical locality. There were sufficient differences in the latter two parameters to explain coexistence by habitat segregation. The peak proportional abundances of seven of the eight species occurred in different latitudinal zones and the degree to which the distribution of each species was overlapped by those of all the other Erythroneura ranged from only 0.10 to 0.63 (° = 0.42). Data indicate that species whose ranges over—lapped substantially have apparently evolved differences in their manner of resource utilization, thus reducing competition through character displacement or through a shift in the adaptive mode of the population. There was a tendency for each species to become more unevenly distributed locally from its distributional center; this further reduced geographical overlap between species. Overall proportional similarities (PS), calculated for latitudinal and local distributions were low (PS range from 0.00 to 0.44; ° = 0.17 where PS_(max) = 1.0 and PS_(min) = 0.0). We infer that habitat segregation in the guild permits coexistence. Additional mechanisms which may permit coexistence are discussed.