An Altered Amphibian Assemblage: Dickinson County, Iowa, 70 Years after Frank Blanchard's Survey

Abstract

-In light of the reports of declines in amphibian numbers we have repeated Blanchard's (1923) survey of the amphibians of Dickinson County, Iowa. We found that five species reported by Blanchard persist: the eastern tiger salamander (Ambystoma tigrinum tigrinum), the American toad (Bufo americanus), the western chorus frog (Pseudacris triseriata triseriata), the gray treefrog (Hyla versicolor/chrysoscelis) and the northern leopard frog (Rana pipiens). Two species reported by Blanchard were not found: the mudpuppy (Necturus maculosus) and Blanchard's cricket frog (Acris crepitans blanchardi). We collected two species not found by Blanchard: the Great Plains toad (Bufo cognatus) and the bullfrog (Rana catesbeiana). The Great Plains toad may have migrated into Dickinson County from the west. The bullfrog was introduced by state fisheries biologists. From descriptions of the turn-of-the-century commercial frogging industry in Dickinson County, we estimate that the number of leopard frogs has declined by at least two, and probably three, orders of magnitude. This decline may be due more to the loss of wetland habitat than past market hunting pressure. In our opinion, the most immediate threat to the existing populations of native amphibians comes from the impact of the introduced bullfrog.