PLEISTOCENE GEOGRAPHY: ceaseless geological and biological change
- Continental, how far south?
- Mountain, how much lower
- Hyrdosphere: Pluvial Lakes: How large?
- Biosphere Vegetation: How far south, where were refugia?
THESIS: Current distributions of organisms primarily reflect the most recent climatic
changes that produced migrations or altered population size.
- historic > neoglacial > Holocene > Pleistocene > Tertiary
(Deevey, 1949 p. 1317) "Of the numerous fallacies that underlie the practice of many biogeographers, the most
fundamental appears to be that of assuming the existing distribution pattern of the species to be as old as the
species itself, or as the genus or family to which it belongs. . . "(However, during the Pleistocene)" there has
been sufficient time, and sufficient transfiguration of geography for the pre-Pleistocene distribution pattern to
be completely transformed in a very large number of cases."
- Deevey was addressing biogeographic bias, of that day, that modern distributions resulted
from continuous populations of the Tertiary
- Asa Gray studied 95 families and 155 genera in common between SE Asia and E U.S.
(and Europe), and attributed this pattern to continuous high-latitude distributions
- E.L. Braun believed that the temperate mesophytic forests of Southeastern U.S. were
unchanged since the Eocene.
Pervasive belief that tropical vegetation remained in place during glaciations (vs. Kam-biu Liu
& Colinvaux 1985; Maley, 1989; Hope et al., 1983; 1980)
- R. Daubenmire traces the eastern and western Plant Formations of North America to
Mio-Pliocene plant distributions
- P. Wells offered, an alternate hypothesis that the distribution of mountain conifers in
Southwest were remnants on once-continuous Tertiary distributions.(vs. Brown, 1971;
Grayson & Madsen, 2000)
EXAMPLES of disjunct populations resulting from Pleistocene distributions:
- "Western" plant species (400 sp) disjunct in Shickshock Mts., Coastal Gaspe,
Labrador. Result from a ± continuous Steppe-Tundra south of Glaciers. (
- Argentina - Southwest U.S. (200 species). Results from ± Continuous Steppe (-Tundra)
at high elevation along tropical highlands. (Cruden, 1966)
- Alpine plants in the Sierra Nevada reached southern limits through semi-continuous
Pleistocene distributions (J. Major and S.A. Bamberg, 1967)
- 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).
LATITUDINAL PLANT MIGRATION AT LAST GLACIAL TERMINATION (I)
- Migration of spruce into Poland during the late glacial (W. Szafer. 1935)
- 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)
- In early Holocene, Lodgepole Pine migrates northward in Canadian Rockies
- In late Holocene Western Red Cedar migrates northward in coastal British Columbia
(Hebda and Mathewes, 1984)
- During late-glacial and Holocene, 6 major northern hardwood species migrated
northward and westward (Davis, 1976).
- Pinyon pine migrates northward during Holocene ? (Tausch et al., 1995) Madsen &
- Major vegetation boundaries also displaced
- prairie-forest border (Bernabo and Webb, 1977; Cushing (1967); Delcourt (1987).
- Great Basin and Mojave Desert: Martin and Mehringer (1965), Betancourt (1990).
PALEOECOLOGICAL IMPLICATIONS: Davis' migration maps have been used as evidence
for individualistic plant dynamics (Gleason, Whittaker): plant species responded
differently to climatic change.
- different starting points
- Jack Pine, Red Pine, Chestnut = Eastern Seaboard Virginia N.Car
- Beech = Florida
- Hemlock, Hickory = Alabama, Louisiana
- different migration rates
- migration lags between climatic change and range adjustment
- composition of late-glacial boreal forest different from modern
- no pine in late glacial boreal forest
TEMPO AND AMPLITUDE OF VEGETATION CHANGE
- European Vegetation
- Sample-sample dissimilarity (Huntley, 1990) indicates greatest change 10K, 0K
- Eastern North America
- Calculate average similarity to modern sample for all sites
- greatest change 13.7, 12.5, 10K, 0K (Jacobsen et al., 1987)
- Western North America
- migration of woodland taxa into Great Basin during Holocene
- Mojave Desert taxa (sagebrush, blackbrush, Joshua tree) in Sonoran Desert
NATURE OF ALTITUDINAL VEGETATION MIGRATION
through last 15,000 yrs vegetation similar to vegetation in area today
The timing of vegetation change differed at high and low elevation
- Uniform: Equal movement by each vegetation zone
1000 m lowering of alpine zone -> 1000 m lowering of steppe
- Compression: Zones migrated at different times or by different amounts.
Steppe and woodland in intermountain basins
- Individualistic: since each species responded differently,
zones of past different from those of today
- Northern Great Basin (Davis, 1983)
Alps show differential migration too
- Grand Canyon Cole (1982)
- qualitatively different Pleistocene and Holocene vegetation
- Europe Carnelli et al., (2004)
Timing of Altitudinal Migration
EFFECT OF CLIMATE:
- Throughout Western North America, tree lines highest in early Holocene (Ritchie et al.,
1983; Kearney & Luckman, 1983; Elias, 1985; Shafer, 1989)
- Eastern North America: 9 - 5 ka, timberline 300-400 m higher in White Mtns, NH (Davis et al., 1980)
ECOLOGICAL BASIS FOR MIGRATION: (Cole, 1985)
- Glacial Maximum: Species up to 1000 km southward, 100 km in West
- Holocene Maximum: Species up to 100 km northward
- Glacial Maximum: Vegetation 1000 m lower
- Holocene Maximum: Species 100 (- 400!) m higher
How did vegetation change take place?
- COMPETITION incoming species displace resident plants who hold on
after optimum climate has changed - VEGETATION INERTIA
- MIGRATION incoming plants occupy niches vacated by emigrating plants
Grand Canyon Woody Species: departures lead arrivals & diversity decreases.
Therefore, migration dominant in vegetation change. BUT, Chihuahuan Desert,
including herbs: diversity increases at 10 K (Shafer, 1991).
- PREDATION southern limit of aspen (Populus tremuloides) displaced
southward after extirpation of bison (Campbell and McAndrews, 1994)