Effect of Euro-American settlement on an insect fauna: Paleontological analysis of the recent chitin record of beetles (Coleoptera) from northeastern Iowa

The effects of Euro-American settlement and associated agricultural activities on a native insect fauna are analyzed through the recent fossil record of beetles in the Roberts Creek drainage basin of northeastern Iowa. Euro-American settlement of this region began in the 1840s, and by 1880 it was under intensive cultivation. The presettlement beetle fauna is characterized by a diverse assemblage of carabids, with species representative of grassland (prairie), woodland, and water-marginal environments. Rich numbers of elmid remains indicate that the presettlement waters of Roberts Creek were clear and cool. As Euro-Americans initiated landscape modification, carabids were replaced as dominant upland elements by weed- and crop-associated weevils and by cattle-associated dung beetles. Synanthropic beetle species, particularly those associated with stored products, and immigrant beetle species, many of which are associated with immigrant host-plant species, now appear in the fossil record. Populations of elmid beetles sharply decline upon settlement, signaling the rapid degradation of Roberts Creek to a polluted, turbid stream. The changes recorded in fossil assemblages at Roberts Creek parallel those at British sites of late Bronze Age, where 2,100 yr ago insect faunas were similarly affected upon transformation of a natural landscape to one of agrarian use.