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Analysis of data collected for a study of prairie dependent Lepidoptera in the northern tallgrass prairies showed four distributional patterns. A logical distributional pattern links species' distribution, i.e. Catocala abbreviatella, to larval host plants. Absence of larval host plant data, which is the case for most species of moths, requires inference based on habitat data of known specimens, i.e. Tarachidia binocula, or in the case of infrequently encountered species, i.e. Crambus murellus, capture data for a limited number of specimens. A fourth distributional pattern, i. e. Atrytone arogos, can be explained by hypotheses which explain the immigration of native grassland species eastward into the Midwest before the last glacial maximum and northward into the Midwest and East Coast from Florida and the Gulf Coast following the last glacial maximum. The hypothesized distributional patterns can be used to predict the occurrence of species in yet,to,be discovered populations along the migration routes as well as explain their absence in other seemingly nearby localities. The widely disjunct distribution, i.e. East Coast and Midwest, of many species, including those not found in prairies, is easily explained by the hypotheses presented here.