Transcript Non-linear responses of vegetation to orbital forcing across the

Non-linear responses of vegetation to orbital
forcing across the temperate to tropical transition
in South America
4th PAGES Open Science Meeting
The Past: A Compass for Future Earth
14th February 2013
K.D. Bennett
Geography, Archaeology and Palaeoecology
Queen's University Belfast
Northern Ireland
Introduction
Two big questions for global biodiversity are:
1. Why do we have millions of eukaryote species?
2. Why are most of them at low latitudes?
'Stability' v ‘change’ as drivers of speciation
How have tropical climates changed over the late Cenozoic?
How did organisms respond?
What are the implications?
Cenozoic global
temperature trends
Overall an erratic cooling,
accelerating towards the
present, with higher
amplitude fluctuations
J. Zachos, M. Pagani, L. Sloan, E. Thomas, and K.
Billups. Trends, rhythms, and aberrations in global
climate 65 Ma to present. Science, 292:686-693,
2001.
Latitudinal variation in insolation 250-0ka BP
Low latitude: 20-kyr cycle dominant
High latitude: 40-kyr cycle dominant
Out of phase
Should lead us to expect
complex patterns of
change by latitude
In phase
A. Berger. Long-term variations of caloric
insolation resulting from the earth's orbital
elements. Quaternary Research, 9:139-167,
1978.
LGM versus modern climates
T: differences large at high
latitude; small at low
latitude, as now or cooler
everywhere
P: variable, some large
differences at low latitude,
both drier and wetter
Annual temp
Precipitation
P. Braconnot, B. Otto-Bliesner, S. Harrison,
S. Joussaume, J.-Y. Peterchmitt, A. AbeOuchi, M. Crucifix, E. Driesschaert, T.
Fichefet, C. D. Hewitt, M. Kageyama, A.
Kitoh, A. Laîné, M.-F. Loutre, O. Marti, U.
Merkel, G. Ramstein, P. Valdes, S. L.
Weber, Y. Yu, and Y. Zhao. Results of
PMIP2 coupled simulations of the MidHolocene and Last Glacial Maximum - Part
1: experiments and large-scale features.
Climate of the Past, 3:261-277, 2007.
Phylogenetic data: Neotropical rattlesnakes
1.85 Ma
1.54 Ma
1.08 Ma
Present
Chronology of
dispersal events in
Crotalus durissus:
gradual spread
over 2 Myr
W. Wüster, J. E. Ferguson, J. A.
Quijada-Mascareñas, C. E. Pook,
M. da Graça Salomão, and R. S.
Thorpe. Tracing an invasion:
landbridges, refugia, and the
phylogeography of the Neotropical
rattlesnake (Serpentes: Viperidae:
Crotalus durissus). Molecular
Ecology, 14:1095-1108, 2005.
Phylogenetic data: mid-high latitude
Spread is a late Quaternary phenomenon
G. Hewitt. The genetic legacy of the
Quaternary ice ages. Nature, 405:907–913,
2000.
Palaeoecological
data: pollen from
High plain of
0
Bogotà
Gradual
spread of
Alnus and
Quercus into
S America
Trees
Shrubs
1
Quercus
2
Lower
amplitude
fluctuations
before 2 Ma
Alnus
3
Age
(Myr)
H. Hooghiemstra. Quaternary
and upper-Pliocene glaciations
and forest development in the
tropical Andes: evidence from a
long high-resolution pollen
record from the sedimentary
basin of Bogotá, Colombia.
Palaeogeography,
Palaeoclimatology,
Palaeoecology, 72:11-26, 1989.
a
The last 16 kyr in southernmost Chile 53.6ºS
Forest (Nothofagus)
Laguna Ballena
10 ka
Shrubs and herbs
S. L. Fontana and K. D. Bennett.
Postglacial vegetation dynamics of
western Tierra del Fuego. The
Holocene 22: 1337-1350, 2012.
The last 16 kyr in south-eastern Brazil 29.5ºS
Forest (Nothofagus)
Rincão das Cabritas
2.9 ka
Herbs
V. Jeske-Pieruschka and H. Behling. Palaeoenvironmental history of the São
Francisco de Paula region in southern Brazil during the late Quaternary inferred
from the Rinc ̃ao das Cabritas core. The Holocene 22: 1251-1262, 2012.
Latitude
Timing of major vegetation change by
latitude in South America
ca 10 ka
Age 14C yr BP
Quaternary response: mid- and high- latitudes
Major climatic changes (and ice-sheets): high amplitude
response to orbital forcing
Pattern of expansion and contraction of forest on 40-kyr
(early Quaternary) to 100-kyr timescales (late Quaternary)
Present patterns completely dominated by the last oscillation
(since 100 ka), most change ca 10-14 ka
Quaternary response: low latitudes
Tertiary: hot (and wet?), ‘stable’
gradual spread
Early Quaternary: cooling, increasing amplitude 20-kyr
oscillations
diversification
Late Quaternary: 100-kyr oscillation superimposed
biome shifts
from northern ice-sheets;
All periodicities: variable amplitude climate, especially
precipitation, response to orbital forcing
Present patterns result from a combination of these three
layers: none is strong enough to dominate continuously
Chaotic behaviour of environmental change at low
latitudes
Characteristics of chaotic systems:
Deterministic (‘butterfly effect’)
Sensitive to initial conditions
Self-similarity
Unpredictable
Cannot rewind
Three levels:
1. Climate system itself
2. Response of ecosystems to climate change
3. Organism interactions
Tropical biodiversity - a necessarily complex model
Periodicities of climate change vary over time
Amplitudes of climate change are relatively small and
variable
Response of vegetation highly variable and not in proportion
to the forcing climate change (‘non-linear’)
No process is strong enough to dominate
Outcomes:
1. Major changes in vegetation happen unpredictably and at
a wide range of times
2. Lineage splitting independent of these changes
Conclusions: consequences
What do we mean by ‘stable’ climate? Equatorial climates of
the Quaternary may be as stable as climate can ever be
The higher diversity of tropical ecosystems is because of this
stability, after all
Biodiversity is, non-linearly:
1. Globally, a function of time (since last mass extinction);
2. Regionally, a function of (relative) ‘stability’;
3. Everything else: the detail.
Processes of developing biodiversity are complex, only
weakly connected to environmental change