Pleistocene and Holocene Epochs (Ice Age)

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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

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Glaciation
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Glaciation
Minor glaciation
Glaciation
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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

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Eccentricity
Obliquity
Periodicity of 100,000 yr
Periodicity of 41,000 yr
Precession
Periodicity of 22,000 yr
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Extent of Glaciation

• Most of Pleistocene and Holocene were glacial
  with short inter-glacial periods

Illinoian
Nebraskan
Wisconsin
Kansan
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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

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Climatic Effects

• Sheer Size of glaciers area covered and height
  (2 3 km) changed wind and current patterns

Lake levels rose in SW US
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Climatic Effects

• Less fluctuation in temperature near glaciers

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Climatic Effects

• Temperatures lower away from equator. Tropic
  drier

How did tropical species maintain and even
increase diversity?
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Sea Level Fluctuations

• Rapid glacial and interglacial fluctuations
• Sea level dropped 100 160 m during glacial
  periods
• Created land bridges

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Retreat of Wisconsin glacier caused rapid rise in
sea level (plus compression of crust, causing sea
water to enter part of Great Lakes
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Result some Atlantic species found in Great
Lakes, including several species of coastal plants
Range of seaside spurge (Ammophlia brevigulata)
note disjunct range
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SHEER MASS - Weight of glaciers compressed crust!!
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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

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Biotas 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

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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)

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Elevational change in Andes. Rise and compression
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Elevational change in SW US mountains
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Change in upper elevational limit of forests
note timing of responses
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Drier Climate recurring theme
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Variation in relative abundance of vegetative
communities since last glacial maximum. Note
variability over time and rapid change.
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Barriers and Corridors

• Changes in biota distribution not uniform
  latitudinally
• North America many corridors
• Mississippi River
• Rocky and Appalachian Mountains

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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

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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 3C)
• Stenothermal species had potential to move to
  opposite poles (Fig. 9.25)

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Aquatic Ecosystems

• 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

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• Lake Agassiz
• Released 163,000 km3 in Tyrrel Sea (Hudson Bay),
  Atlantic Ocean
• Also down Glacial River Warren (now Minnesota and
  Mississippi Rivers)

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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)

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Refugia

• Safe zones or habitats, offered areas where ice
  did not cover, even in the area of the ice sheet
• Haffers 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

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Emphasis is on distribution of subspecies and
number of endemic species
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Nunatuks
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Refugia and Endemics
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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

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Glaciation and Extinctions

• Marine Invertebrates also most extinctions at
  the onset of glacial events
• Causes
• Stenothermal species
• Limited ability to disperse (non-planktonic
  larvae)

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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
  sized-terrestrial vertebrates was low and
  constant until the late Wisconsin

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Australia Black extinct during
Pleistocene/early Holocene Shaded extinct or
endangered after European colonization White
Extant, non-endangered species
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