Biodiversity responses

to past changes in

climateGuy F Midgley

SANBI

Climate

change is

nothing new

(Milankovitch

theory)

We live in an unusual, stable climate

We live on a predominantly cool-adapted planet!

How do

we

know

all this?

Ice cores can tell

us about

prehistoric climate

conditions

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

How might these changes have

affected biodiversity?

Migration

Hewitt (2000) Nature 405: 907-913

Global features, Last Glacial Maximum

(21-18 kbp)

R

e

s

i

d

u

a

l

p

l

a

n

t

p

o

p

u

l

a

t

i

o

n

s

i

n

t

h

e

W

e

s

t

e

r

n

C

a

p

e

Davis and Shaw (2001) Science 292: 673-679

Historic pollen distributions

Current biodiversity reveals the imprint

of these changes

Myers et al (2000) Nature

6 kBP + 0.05ºC

12 kBP - 1.82ºC

18 kBP - 3.67ºC

General Circulation Model (CCM0)

Climate reconstruction – Temperature

Climate reconstruction – Rainfall

2.5º

Species/biome

distribution

#re

cord

s

34o 36o

Maximum temperature

Max temp envelope

Maximum

temperature

34o 36o

Climate space modeling, bioclimatic

modeling, niche modelling

Correctly modelled = 0.76

MAR, Tmin, WB, %Win rain

Fynbos bioclimatic envelope

Correctly modelled = 0.75

Succulent Karoo bioclimatic envelope

Time before present (Kya)

0

6

+0.05ºC

12

-1.82ºC

15

18

-3.67ºC

The succulent Karoo biome advanced as

temperature increased

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?

From Lovegrove (1993)

Centres of endemism and stable climate

18 k BP

The Knersvlakte

Karoo plants evolved incredibly fast

Recent diversity is huge

NB: this

dendrogram

describes only the

evolution of

Ruschias, not all

mesems.

Mechanistic modelling

What about CO2 and other effects?

Savannas: CO2 and fire

Climate

CO2

Soil

PHYSIOLOGY

BIOPHYSICS

WATER & NUTRIENT

FLUXES

PLANT

STRUCTURE

&

PHENOLOGY

DISTURBANCE

VEGETATION

DYNAMICS

Factors of a mechanistic model

DVM – dynamic vegetation model

Sheffield DGVM

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

Fire on

Fire off!

The role of fire in Savanna ecosystems

mapped by ATSR-2 World Fire Atlas (European

Space Agency)

Global distribution of fire in 1998

CO2 crisis for C3, woody plants

Paleo temp change

Ice core image

Low CO2 limits tree

growth relatively more

than herbaceous plant

growth

Under a fire regime, woody plants over a

certain height may survive burning

Bond & Midgley 2001,

Global Change Biology

Simulated effects of CO2 on stem height

(Mesic savanna)

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

Modelled tree cover response to CO2

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

Empirical experiments

Barney Kgope NBI

Low CO2 discriminates against woody

plants

550 ppm 180 ppm

Acacia karroo

High CO2 boosts

productivity

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]

Plant response

Trees have increased in grasslands worldwide.

Open savanna, S. Africa, 1955

Same place, 1998

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

Check your understanding of Chapter 4

PASS MARK 80%

Please do not proceed further until you have PASSED

Chapter 4: test yourself

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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