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4/10/12
Global Change & Evolution
Evolution BY2024, Trevor Hodkinson
Reading
Campbell ‘Biology’ esp. Chapter 25, History of Life on Earth.
Hodkinson et al. ‘Climate Change, Ecology and Systematics’ Ch.1 & 7
Beerling ‘The Emerald Planet’
Purves et al. ‘Life’
Skelton ‘Evolution’
The History of Life
4600mya
Earth
formed
5000 million
years ago
4000mya
Life
4000
2700mya
Photosynthesis
starts producing
oxygen
3500mya
Oldest
prokaryote (?)
3000
3800mya
Oldest
rock
2100mya
Eukaryotes
¾ of life’s history was
single celled.
See Endosymbiosis
lecture for origin of
Eukaryotes
2000
543mya
Cambrian
Explosion, Oxygen
increases
dramatically
1500mya
Multicellularity
1000
Now
Snowball Earths
possibly until 650mya
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Life evolved for most of its history in a world very different from
today –global change is the norm
Abiotic change atmosphere (inc. O2, CO2), geology/plate
tectonics, climate
Biotic change photosynthesis, biome change, origination/
extinction
Influenced origination and extinction of life on earth
Atmosphere: Oxygen, cyanobacteria and plants
Cyanobacteria evolved photosynthesis,
i.e. splitting water to make oxygen.
One group survives today as stromatolites
and thrombolites (W. Australia). Fossils
from 2700mya.
Oxygen is toxic to most other bacteria, so they poisoned almost
everything else. It also made an ozone atmosphere.
The ozone in the
atmosphere protected the
land from UV light and so
made it habitable to plants
etc
They helped raise the oxygen levels further (– see “Life’s a Gas”
article), allowing larger animals onto land.
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Major origination events: the Ediacaran Fauna
550mya
After the last ever “Snowball
Earth”, find suddenly a
whole fauna/flora of flattened
multicellular species and
bacterial mats.
No predation as all feeding
was by absorption, no guts!
Disappeared suddenly and
replaced by…
Major origination event: the Cambrian Explosion
…loads of very diverse
species with complex
bodies, heads, guts,
mouths, legs, hard
carapaces.
What sparked this
diversity? O2 increase,
predator prey coevol, and
evol of Hox gene complex
(key innovation)
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The Burgess Shale shows all the basic
body designs we have now, and many
which have gone extinct…. Much was
invented in the Cambrian Explosion
Read “When we
were worms” New
Scientist 18th Oct
1997 pp30-35
Or was it?
Giant insects
Meganeura
wingspan
63cm
Carboniferous
Due to
cyanobacteria
Due to algae/
land plants/
cyanobacteria
David Beerling-Emerald
Planet, Oxford Univ. Press
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Plate tectonics/ geochemical factors
Changes climate/atmosphere and influences extinction /speciation
eg. Volcanic activity (extinctions; Permian) and Vicariance (speciation)
Tectonics contribute to
‘Vicariance’
Formation of species from populations
that were once continuous but have since
become divided by the creation of natural
barriers
(e.g new oceans) which prevent
populations mixing.
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Historical biogeography
E.g.Geographic distributions of
plant species can seem ‘strange’
until plate tectonics are
considered.
Example 1 Platanus –vicariance
and allopatric speciation (see
Plant Evolution lecture)
NALB
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Nothofagus -disjunct distribution
N. antarcticus, related to
beech (Fagus)
Dispersal or
vicariance?
Continental drift –break up of
Gondwanaland
160 MYA (before angiosperms)
60 mya
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Evolution of Nothofagus species
most likely caused by ‘vicariance’
Plate tectonics causing allopatric
speciation and geographical isolation
Evidence: Fossils and branching pattern
on phylogenetic tree matching timing of
separation of plates
Tectonics also influence ‘Realms’
Large regions where life has been evolving in relative
isolation for a long period of time separated by geographical
features e.g. Oceans, broad deserts, high mountain ranges
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Floristic realms
Holoarctic
Paleotropics
Neotropics
Capensis
Australis
Example of realms
Unique flora of South America and
Australia –islands for 100 my
• Podocarpaceae e.g. Araucaria southern hemisphere
• Taxodiaceae and Pinaceae –northern
hemisphere
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Climate influences evolution and determines biomes
Distinctive ecological zones governed by temp. and
precipitation (organisms are adapted to these biomes)
Rainforest biome
If precipitation in the
tropics is even and high
throughout the year it
supports rainforest
Organisms are adapted
to specific conditionsnatural selection.
e.g Shade tolerant
palms.
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Phanerozoic was period when ‘complex’ life forms were
evolving post Cambrian explosion –expect shifts in biomes
Jurassic (c.200-150mya)
Global vegetation biomes
Thus biomes shift with
climate and organisms
adapt to new environments
winterwet
Cool
Warm
temperate temperate
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CO2
Cenozoic
temperature and CO2
Antartica explored
by Scott who
collected many
Tertiary fossils
Beardmore
glacier 82ON
Robert F. Scott
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Early Tertiary polar forest
Peninsula Antartica like Valdivian rainforests of Southern
Chile. That once stretched across Antarctica to Australia.
Forests also found in high arctic in Canada and Greenland
(striking distance from poles). 45mya Metasequoia (dawn
redwood).
Araucaria
Nothofagus
Valdivian rainforests of
S. Chile
Cryolophosaurus
‘Elvisaurus’
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Adaptation to changing
climate/atmosphere
Grasses were winners in global change during the Tertiary
Evolved dispersal ability, grazing tolerance, fire resistance,
and novel ways of doing photosynthesis (C4 or C3)
Tertiary witnessed the rise of grasses / grasslands
•  Savanna/tropical
grassland 20% of land
surface (and rising)
•  Savanna dominating in
last 10-20million years
•  Success due to C4
grasses –distribution shown below
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Evolution of C4 photosynthesis
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in tropics
C4 photosynthesis
Alternative photosynthetic
pathway with leaf ‘bundle
sheath’ leaf Kranz anatomy
Bundle sheath
<=1>?
CO2 first incorporated into 4
carbon (C4) compounds (by
PEP; phosphoenolpyruvate)
(C3 phosphoglycerate)
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climates and lower CO2
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Where did C4 originate?
When did it originate?
Phylogenetic reconstructions can show
us this.
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C4 evolved
independently 12
times (4,500 spp.)
Dated tree
calibrated with
fossils
First in Africa 30
mya
Many times
subsequently from
20-10 mya with rise of
savanna (C isotope
evidence from fossil
tooth enamel).
C4 evol
AF=AFRICA
Bouchenak-Khelladi et al.
2010 Bot J. Linn Soc.
Twelve shifts to C4 photosynthesis can be detected
starting 30mya
Shifts in
photosynthesis
numbers 1-12
Orange=C4
Blue=C3
Past CO2
Rise of C4
savanna
grasslands c.
10-20 mya
Appearance of C4
coincides with
steep CO 2
decline
Also due to
aridification and
increased fire.
Bouchenak-Khelladi et al. 2008.
Global Change Biology Biology
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THE FUTURE?
Quaternary ice core info
LGM
Vostok 3.6km deep
core through ice
(420,000yrs)
EPICA DOME C
(EDC) goes deeper
and back 750,000yrs.
Deuterium (D) and
oxygen (O) isotopes are
temperature proxies
Consequences of climate change at
species/population level
‘Shall I stay or shall I go survival strategy’
M. Jones (1982) Shall I stay or shall I go?Combat Rock, The Clash.
IF=3.5 million
•  Stay: Selective pressure (evolve/
adapt)
•  Go: Migratory pressure (move)
Combination of the two?
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GO: Ecological niche modelling to
predict where and if species can move
Take present day distribution and
ecological info to predict the future under
global change scenario
Present day Fraxinus
(ash) hybrid
Double CO2,
year 2100
Thomasset et al. 2011 in Climate Change Ecology and Systematics
“If I stay there will be trouble”
Trouble unless species adapt/evolve
“If I go there will be double”
Double trouble if species migrate with nowhere to go
A concern because of habitat loss/fragmentation
If none of these occur then extinction is inevitable
M. Jones (1982) Shall I stay or shall I go? The Clash
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how much habitat
remains and how
will species
move?
Important
Bird Areas
(IBAs)
Mean potential turnover
of 1600 priority bird
species by 2085 under
global warming
scenario –indicates
large shifts in potential
range
Ploceus
temporalis
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Global change now
6th mass extinction?
(caused by climate change, habitat
loss, human population growth,
pollution)
Mass Extinctions
5 really big extinction events of
multicellular life
All associated with global change /
sea level changes
Date
% genera
lost
% species
lost
Main groups going extinct
End of
Ordovician
61
85
Major groups of trilobites, brachiopods, corals,
echinoderms etc.
End of
Devonian
55
82
21% or marine families
End of
Permian
84
96
57% of marine families; all reefs, all trilobites, 27
families of tetrapods
End of
Triassic
47
76
58 families of cephalopods, many reptiles, all large
amphibians, many insect families
End of
Cretaceous
47
76
Dinosaurs and ammonites gone. Flowering plants and
marine groups decimated. Few land animal phyla left.
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All genera
Well defined genera
Big five
Other mass extinctions
Millions years
Thousands of
genera
Origination delayed after extinction but
life recovers (life highly resistant –never totally eclipsed and can recover
readily)
Conclusions
• The history of life on earth has been dominated by
global change
• Abiotic and biotic factors both important
Atmosphere (O2, CO2)
Plate tectonics (vicariance)
Climate
Interactions of these with life
• Future depends on ability of life to adapt or migrate
(Shall I stay or shall I go strategies)
• Fossil record shows five major extinctions of
multicellular life but life never wiped out and does
recover
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What caused the K-T extinction (killed the dinosaurs)?
  Asteroid
10km across hits earth: equivalent to all atomic
bombs exploding
  Dust cloud hides sun – nuclear winter
  Explosion fumes make acid rain
  Acid rain kills forests and increases greenhouse gasses
  Greenhouse effect causes global warming
  Ecosystem collapse
Whole event took 400,000 years, with asteroid in the middle
of that time, so it was only one of several causes.
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