Meeting Abstract

P2.7  Friday, Jan. 4  Glacial History of Lake Michigan: Influence on Distribution of Island Land Snails PEARCE, TA; VON DASSOW, YJ*; Carnegie Museum of Natural History; Carnegie Museum of Natural History yasmin.vondassow@gmail.com

The influence of past climatic conditions is manifested in current distributions of organisms. Assemblages of land snails on the islands of Lake Michigan have captured a snapshot of historical conditions. We examined the four largest species of land snails on eleven islands and the mainland: Anguispira alternata, Neohelix albolabris, Mesodon thyroidus, and Haplotrema concavum. Census data show that all four species occur on the mainland; only A. alternata and N. albolabris occur on the islands, with minor exceptions. The ranges of all four species overlap, but A. alternata and N. albolabris have ranges that extend further north while the other two species have ranges that extend further south. This suggests that the former two are more cold-adapted and the latter two are more warm-adapted. The glacial history of the northern Lake Michigan area combined with current distributions of the four species suggests the following scenario. At 11,500 ybp the area was covered by a glacier several kilometers thick, at which point no land snails were present. At 9,500 ybp, the islands were exposed but connected to the mainland. As temperature rose, populations of A. alternata and N. albolabris dispersed northwards on the heels of the glacier. Subsequent isostatic rebound and lake level rise flooded the area around the islands, cutting them off from the mainland. When the warm-adapted M. thyroidus and H. concavum migrated into the area, dispersal to the islands was more difficult due to the lake level.