Habitat associations of sympatric violet-feeding fritillaries (Euptoieta, Speyeria, Boloria) (Lepidoptera: Nymphalidae) in tallgrass prairie

Abstract

At 106 tallgrass prairies in the midwestern USA, 18,055 individuals of six fritillary species (Lepidoptera: Nymphalidae) were counted in 552.9 hr and 987.1 km of transect survey effort from 14 June to 13 September during 1988-96. The relative abundance of Euptoieta claudia, Speyeria cybele, S. aphrodite, S. idalia, Boloria selene, and B. bellona was analyzed for significant patterns relative to five habitat factors. Topographic diversity (i.e., whether the site was uniform or contained both uplands and lowlands) produced the most significant effects. Prairie patch size and vegetation type (wet, mesic, dry) also produced numerous significant patterns. When management type was significant, burning alone or in combination with another management was associated with lower densities, non-management with intermediate or higher densities, haying and grazing with higher densities. Vegetative quality (i.e., degree of floristic degradation) produced the fewest significant patterns. Three of four testable fritillary species significantly and positively correlated in abundance with one or more species of Viola (Violaceae) (violets). Most correlations were with particular violet species, not combined violet abundance, suggesting that the fritillaries segmented violet resources (their larval food) by species and/or habitat. The two most abundant violet species, V. pedata and V. pedatifida, and violets in general, occurred in more sites than any of the fritillary species did. The species most restricted to tallgrass prairie, S. idalia, was relatively denser in dry prairie vegetation in larger prairie patches with topographic diversity and management by haying or grazing.