Transcript Glaciation and Biogeography of Pleistocene

Pleistocene and Holocene Epochs (Ice Age)
• Period of marked change in species despite
short duration
• Recent event  relates to current species
• Traceable change through tree rings, animal
and human middens, pollen, marine
indicator species
• Also important because event did not
obliterate record of past events
Glaciation
Glaciation
Minor glaciation
Glaciation
Causes of Glaciation
• Earlier glaciations caused by contiental drift
• Continents 2 mya near/in current positions
• Once thought Pleistocene glaciation caused
by changes in solar output
• Relatively stable solar output for last 590
million years (Gates 1993)
• Been linked to Milankovich cycles + albedo
Eccentricity
Obliquity
Periodicity of 100,000 yr
Periodicity of 41,000 yr
Precession
Periodicity of 22,000 yr
Extent of Glaciation
Nebraskan
• Most of Pleistocene and Holocene were
glacial with short inter-glacial periods
Extent of Glaciation
• 80% of glacial ice in Northern Hemisphere
– North America, Europe, Atlas Mtn. (NW
Africa)
• Southern Hemisphere
– Chile and Argentina
– Australia – limited to Victorian Alps, Central
Plateau of Tasmania
– New Zealand Alps
Climatic Effects
• Sheer Size of glaciers – area covered and
height (2 – 3 km) changed wind and current
patterns
Lake levels rose in SW US
Climatic Effects
• Less fluctuation in temperature near
glaciers
Climatic Effects
• Temperatures lower away from equator.
Tropic drier
How did tropical species
maintain and even
increase diversity?
Sea Level Fluctuations
• Rapid glacial and interglacial fluctuations
• Sea level dropped 100 – 160 m during
glacial periods
• Created land bridges
Retreat of Wisconsin glacier caused rapid rise in sea level
(plus compression of crust, causing sea water to enter part
of Great Lakes
Result – some Atlantic species found in Great Lakes,
including several species of coastal plants
Range of seaside
spurge (Ammophlia
brevigulata) – note
disjunct range
SHEER MASS - Weight of glaciers compressed crust!!
Biogeographic Responses to Glaciation
• Biogeographic dynamics of Pleistocene
triggered by:
• Changes in location, extent, and
configuration of a species prime habitat
• Changes in the nature of climatic and
environmental zones
• Formation and closing of dispersal routes
Biota’s Response to Glaciation
• Species were adapted to long-term
conditions of relative stable climates,
reponses were:
• Able to “float” with their optimal habitat as
it shifted
• Remained in in same location and adapted
to new conditions
• Range reduction and extinction
• See Box 9.1
Biogeographic Responses to Glaciation
• Some vegetative and marine zones increased
they areal coverage
• Steppes, savannahs  open-canopied
ecosystems (generally drier climate)
• Closed-canopy ecosystems generally
decreased (especially tropical rain forests
• Changes greatest in mid-latiturdes (35 to
55°)
Elevational change in
Andes.
Rise and compression
Elevational change in SW US
mountains
Change in upper
elevational limit of
forests – note timing of
responses
Drier Climate – recurring theme
Variation in relative abundance of vegetative communities since
last glacial maximum. Note variability over time and rapid
change.
Barriers and Corridors
• Changes in biota distribution not uniform
latitudinally
• North America – many corridors
– Mississippi River
– Rocky and Appalachian Mountains
Barriers and Corridors
• Changes in biota distribution not uniform
latitudinally
• Eurasia – corridors
– Ural, Carpathian, and Atlay mountains
– Rocky and Appalachian mountains
• Eurasia – barriers
– Mediterranean Sea
– Caucasus, Alps, and Pyrenees mountains
Corridors and Dispersal
• Lowering of elevation of montane vegetative
zones as mechanisms of dispersal – cross to
other mountains and mesic lowlands
• Oceanic zonal patterns also changed (Fig.
9.12) even though open ocean temperature
change smaller (2 – 3°C)
• Stenothermal species had potential to move
to opposite poles (Fig. 9.25)
Aquatic Ecosystems
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Glaciers are major lake builders
Seen as aftermath of glaciation
Kettle lakes, moraine lakes, paternoster….
Glacial lakes
– Meltwater retained by ice dams
– When dams break  large mass freshwater
into shallow seas, carve out river valleys
• Lake Agassiz
• Released 163,000 km3
in Tyrrel Sea (Hudson
Bay), Atlantic Ocean
• Also down Glacial
River Warren (now
Minnesota and
Mississippi Rivers)
“Wet Aridlands” – Pluvial Lakes
• Formed in what are now deserts
• Large freshwater or saline lakes
• Caused by low evaporation + high
precipitation
• Typically formed in broad basins between
mountain ranges
• Lake Bonneville – remnants are saline lakes
(Great Salt Lake)
Refugia
• “Safe” zones or habitats, offered areas where ice
did not cover, even in the area of the ice sheet
• Haffer’s Pleistocene refugium hypothesis
– Fragmentation of Amazonian rainforest by
precipitation levels
– Lead to isolation and divergence of species and
subspecies
• New model – inundation of basin by 100 m rise in
sea level and Amazon islands
Emphasis is on distribution of subspecies and
number of endemic species
Nunatuks
Refugia and Endemics
Glaciation and Extinctions
• Plants – most extinctions at the onset of
glacial events
• Species persistence by
– Disperse with climatic zones
– Refugia and dispersal
– Adaptation to new conditions
Glaciation and Extinctions
• Marine Invertebrates – also most
extinctions at the onset of glacial events
• Causes
– Stenothermal species
– Limited ability to disperse (non-planktonic
larvae)
Glaciation and Extinctions
• Terrestrial vertebrates – pattern less clear
• Overkill hypothesis – impact of humans as
they expanded their range. Would lead to
loss of large herbivores as well as their
associated predators and scavengers
• Size-Space
• Climate – many of extinctions of all sizedterrestrial vertebrates was low and constant
until the late Wisconsin
Australia:
Black – extinct during Pleistocene/early Holocene
Shaded – extinct or endangered after European
colonization
White – Extant, non-endangered species