PLEISTOCENE GEOGRAPHY: ceaseless geological and biological change
THESIS: Current distributions of organisms primarily reflect the most recent climatic changes that produced migrations or altered population size.
EXAMPLES of disjunct populations resulting from Pleistocene distributions:
  1. "Western" plant species (400 sp) disjunct in Shickshock Mts., Coastal Gaspe, Labrador. Result from a ± continuous Steppe-Tundra south of Glaciers. ( Fernald, 1925)
  2. Argentina - Southwest U.S. (200 species). Results from ± Continuous Steppe (-Tundra) at high elevation along tropical highlands. (Cruden, 1966) amphitropical
  3. Alpine plants in the Sierra Nevada reached southern limits through semi-continuous Pleistocene distributions (J. Major and S.A. Bamberg, 1967)
  4. Great Basin, Rocky Mountains, and Sierra Nevada populations of mammals were connected during the Pleistocene. At the Pleistocene - Holocene boundary dispersal routes disappeared and extinctions begin (Brown, 1971). sky islands

LATITUDINAL PLANT MIGRATION AT LAST GLACIAL TERMINATION (I)

  1. Migration of spruce into Poland during the late glacial (W. Szafer. 1935)
  2. Jack pine was absent from full-Glacial Boreal forest of the upper Midwest (no analog). White pine migrated into Minn. from the E. U.S. (Wright, 1968)
  3. In early Holocene, Lodgepole Pine migrates northward in Canadian Rockies
  4. In late Holocene Western Red Cedar migrates northward in coastal British Columbia (Hebda and Mathewes, 1984)
  5. During late-glacial and Holocene, 6 major northern hardwood species migrated northward and westward (Davis, 1976).
  6. Pinyon pine migrates northward during Holocene ? (Tausch et al., 1995) Madsen & Rode 1990
  7. Major vegetation boundaries also displaced

PALEOECOLOGICAL IMPLICATIONS: Davis' migration maps have been used as evidence for individualistic plant dynamics (Gleason, Whittaker): plant species responded differently to climatic change.
  1. different starting points
  2. different migration rates
  3. composition of late-glacial boreal forest different from modern

TEMPO AND AMPLITUDE OF VEGETATION CHANGE


NATURE OF ALTITUDINAL VEGETATION MIGRATION

  1. Uniform: Equal movement by each vegetation zone
  2. Compression: Zones migrated at different times or by different amounts.
  3. Individualistic: since each species responded differently,

  4. Northern Great Basin (Davis, 1983)
  • through last 15,000 yrs vegetation similar to vegetation in area today
  • The timing of vegetation change differed at high and low elevation

    Alps show differential migration too