biodiversity responses to past changes in climateplanet.uwc.ac.za/nisl/ess_2020/ess221/ess221...
TRANSCRIPT
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Biodiversity responses
to past changes in
climateGuy F Midgley
SANBI
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Climate
change is
nothing new
(Milankovitch
theory)
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We live in an unusual, stable climate
We live on a predominantly cool-adapted planet!
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How do
we
know
all this?
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Ice cores can tell
us about
prehistoric climate
conditions
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Carbon dioxide
Measurements of global CO2 levels
from Mauna Kea Observatory in
Hawaii have been increasing steadily
since recording began in the 1950s.
Analysis of ice cores shows that
current CO2 levels are significantly
higher than at any time in the past
450 000 years, and should be
doubled by the middle of this
century.
It is clear that this effect is
anthropogenic (caused by human
activity).
Click to enlarge
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How might these changes have
affected biodiversity?
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Migration
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Hewitt (2000) Nature 405: 907-913
Global features, Last Glacial Maximum
(21-18 kbp)
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R
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Davis and Shaw (2001) Science 292: 673-679
Historic pollen distributions
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Current biodiversity reveals the imprint
of these changes
Myers et al (2000) Nature
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6 kBP + 0.05ºC
12 kBP - 1.82ºC
18 kBP - 3.67ºC
General Circulation Model (CCM0)
Climate reconstruction – Temperature
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Climate reconstruction – Rainfall
2.5º
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Species/biome
distribution
#re
cord
s
34o 36o
Maximum temperature
Max temp envelope
Maximum
temperature
34o 36o
Climate space modeling, bioclimatic
modeling, niche modelling
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Correctly modelled = 0.76
MAR, Tmin, WB, %Win rain
Fynbos bioclimatic envelope
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Correctly modelled = 0.75
Succulent Karoo bioclimatic envelope
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Time before present (Kya)
0
6
+0.05ºC
12
-1.82ºC
15
18
-3.67ºC
The succulent Karoo biome advanced as
temperature increased
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6
12
18
0
2
4
6
8
10
12
14
0 5000 10000 15000 20000
Time (kya)
Restionaceae Ericaceae
------------ traces of both groups ----------
1
1
Shi et al (1998)
Pollen
evidence?
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From Lovegrove (1993)
Centres of endemism and stable climate
18 k BP
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The Knersvlakte
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Karoo plants evolved incredibly fast
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Recent diversity is huge
NB: this
dendrogram
describes only the
evolution of
Ruschias, not all
mesems.
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Mechanistic modelling
What about CO2 and other effects?
Savannas: CO2 and fire
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Climate
CO2
Soil
PHYSIOLOGY
BIOPHYSICS
WATER & NUTRIENT
FLUXES
PLANT
STRUCTURE
&
PHENOLOGY
DISTURBANCE
VEGETATION
DYNAMICS
Factors of a mechanistic model
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DVM – dynamic vegetation model
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Sheffield DGVM
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Sheffield DGVM
(Woodward)
Climate
CO2, N
Soil
PHYSIOLOGY
BIOPHYSICS
WATER & NUTRIENT
FLUXES
PLANT
STRUCTURE
&
PHENOLOGY
DISTURBANCE
VEGETATION
DYNAMICS
Woodward FI, Smith TM, Emanuel WR (1995) Global
Biogeochemical Cycles, 9, 471-490
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Fire on
Fire off!
The role of fire in Savanna ecosystems
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mapped by ATSR-2 World Fire Atlas (European
Space Agency)
Global distribution of fire in 1998
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CO2 crisis for C3, woody plants
Paleo temp change
Ice core image
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Low CO2 limits tree
growth relatively more
than herbaceous plant
growth
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Under a fire regime, woody plants over a
certain height may survive burning
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Bond & Midgley 2001,
Global Change Biology
Simulated effects of CO2 on stem height
(Mesic savanna)
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Implications and tests
Past contraction of woody elements with low CO2
(180ppm) – paleoecological record
Bush encroachment since the pre-industrial, and
into the future – empirical experiments
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Modelled tree cover response to CO2
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Wonderkrater pollenScott, L. (2002)
0
10
20
30
40
50
60
24340 22040 14180 9640 8390 6330 1000
Years BP
sa
va
nn
a t
ree
po
lle
n %
180 - 200 260-280
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Empirical experiments
Barney Kgope NBI
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Low CO2 discriminates against woody
plants
550 ppm 180 ppm
Acacia karroo
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High CO2 boosts
productivity
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CO2 level
controls
carbon
investment
in defenses
0
0.5
1
1.5
2
0 200 400 600 800 1000 1200
[CO2] ppm
Resp
on
se r
ati
o (
370 p
pm
)
A.karoo
A.nilotica
0
1
2
0 200 400 600 800 1000 1200
[CO2] ppm
Resp
on
se r
ati
o (
370 p
pm
)A.nilotica
Thorn length
Foliar [tannin]
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Plant response
Trees have increased in grasslands worldwide.
Open savanna, S. Africa, 1955
Same place, 1998
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Conclusions Climate and CO2 has changed in the past –
sometimes rapidly!
However, for the past 2 million years change has been fairly strictly bounded
Species have tended to migrate to track past changes, there is occasional evidence of in situadaptation/speciation – not relevant in a conservation context
It’s not only climate, but CO2 and fire (and other changes) that can affect biodiversity –management matters
We need to view all biological response models with skepticism, taking into account the assumptions and uncertainties
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Check your understanding of Chapter 4
PASS MARK 80%
Please do not proceed further until you have PASSED
Chapter 4: test yourself
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Chapter 1 The evidence for anthropogenic climate change
Chapter 2 Global Climate Models
Chapter 3 Climate change scenarios for Africa
Chapter 4 Biodiversity response to past climates
Chapter 6 Approaches to niche-based modelling
Chapter 5 Adaptations of biodiversity to climate change
Chapter 7 Ecosystem change under climate change
Chapter 8 Implications for strategic conservation planning
Chapter 9 Economic costs of conservation responses
I hope that found chapter 4 informative, and that you enjoy chapter 5.
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