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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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C4 photosynthesis Alternative photosynthetic pathway with leaf ‘bundle sheath’ leaf Kranz anatomy
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CO2 first incorporated into 4 carbon (C4) compounds (by PEP; phosphoenolpyruvate) (C3 phosphoglycerate)
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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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