Evolution in a Glaciated Landscape: Contribution of Endemism to Great Lakes Biodiversity
Peirson, J. A. .
The Evolution of Great Lakes Region Endemic Plants: Influences of Postglacial Migration and Ecological Differentiation.
Despite the geologically nascent formation of the Great Lakes landscape, more than 40 endemic plants have been described from the region. Early hypotheses proposed that these endemics were Tertiary relicts that survived glaciation on the summits of ice-free nunataks. After geologic evidence squarely disproved the nunatak hypothesis, the general consensus about the origin of Great Lakes endemics shifted. For the last half century, it has been commonly regarded that endemics evolved from small founder populations following the recession of the Laurentide ice sheet less than 15,000 years ago. Population genetic studies have not disproved this hypothesis, but on the whole, critical knowledge of the origins, evolution, and taxonomy of these taxa is lacking. I review the endemic flora of the Great Lakes region and use geographic and habitat distributions to examine the influences of postglacial migration and ecological differentiation on current patterns of variation. Examination of geographic distributions reveals that most Great Lakes region endemics are centered on the northern boundary of the Niagara escarpment. Southeastern parts of the region harbor significantly fewer endemics. Geographic range size varies among endemics. Some (e.g., Linum medium var. medium and Solidago houghtonii) are very narrowly distributed, while others are widespread throughout the region (e.g., Hypericum kalmianum and Solidago ohioensis). The current distributions of the endemics and the distributions of their proposed relatives suggest that ancestors of the endemic taxa migrated into the region from different glacial refugia. Population distributions also reveal that almost all endemics are restricted to edaphically stressful Great Lakes shorelines (or former shorelines) and otherwise glacially influenced habitats. Examples are given from ongoing studies of the Solidago simplex species complex in the Great Lakes region. This group exemplifies how both postglacial migration and edaphic differentiation have fostered the evolution of regionally endemic species.
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1 - University of Michigan, Department of Ecology & Evolutionary Biology, 830 North University Avenue, Ann Arbor, Michigan, 48109-1048, USA
Great Lakes region.
Presentation Type: Symposium or Colloquium Presentation
Location: Boulevard A/Hilton
Date: Tuesday, July 10th, 2007
Time: 9:00 AM