Stanton-Geddes, John , Tiffin, Peter , Shaw, Ruth .
Ecological and genetic contributions to range limits in Chamaecrista fasciculata.
The stability of species range limits is a conundrum to evolutionary biologists: what limits species from expanding their ranges via adaptation to conditions beyond the range edge? Theoretical and empirical work suggest that both ecological and evolutionary forces can be involved in the stability of range edges. We examined these processes on limiting range expansion of the native annual legume Chamaecrista fasciculata at its northern and western range edges in the Upper Midwest of the United States. First, to determine the relative importance of abiotic (e.g. climate) and biotic (e.g.competitors) factors, we established experimental populations simulating a colonization event with seeds transplanted into sites within the range, at the northern and western range edges, and beyond both these edges. At each site, we reduced neighboring vegetation in half the experimental populations. The results demonstrate that absolute fitness is below population replacement beyond both range edges, but that the effect of neighbors varies from facilitative to competitive at different life-history stages. Second, we evaluated population structure and gene flow between populations within the range and at the range edge using sequence data from nine nuclear loci. The results suggest that these populations are not at equilibrium, with evidence for a stepping-stone model of poleward range expansion in response to Pleistocene glacial retraction. Overall, these results suggest that the distribution of C. fasciculata is limited by a combination of ecological factors reducing absolute fitness at the range edge, and genetic factors reducing adaptive potential to these environments.
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1 - University of Minnesota - Twin Cities, Ecology, Evolution and Behavior, St. Paul, MN, 55108, USA
2 - University of Minnesota - Twin Cities, Plant Biology, St. Paul, MN, 55108, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Portland Room/Chase Park Plaza
Date: Monday, July 11th, 2011
Time: 1:45 PM