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Non-linear responses of vegetation to orbital forcing across the temperate to tropical transition in South America 4th PAGES Open Science Meeting The Past:

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Presentation on theme: "Non-linear responses of vegetation to orbital forcing across the temperate to tropical transition in South America 4th PAGES Open Science Meeting The Past:"— Presentation transcript:

1 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

2 Introduction How have tropical climates changed over the late Cenozoic? How did organisms respond? What are the implications? 'Stability' v change as drivers of speciation 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?

3 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. Cenozoic global temperature trends Overall an erratic cooling, accelerating towards the present, with higher amplitude fluctuations

4 A. Berger. Long-term variations of caloric insolation resulting from the earth's orbital elements. Quaternary Research, 9:139-167, 1978. Latitudinal variation in insolation 250-0ka BP High latitude: 40-kyr cycle dominant Low latitude: 20-kyr cycle dominant In phase Out of phase Should lead us to expect complex patterns of change by latitude

5 P. Braconnot, B. Otto-Bliesner, S. Harrison, S. Joussaume, J.-Y. Peterchmitt, A. Abe- Ouchi, M. Crucix, 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 Mid- Holocene and Last Glacial Maximum - Part 1: experiments and large-scale features. Climate of the Past, 3:261-277, 2007. LGM versus modern climates Annual tempPrecipitation 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

6 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: Neotropical rattlesnakes Chronology of dispersal events in Crotalus durissus: gradual spread over 2 Myr 1.85 Ma 1.54 Ma 1.08 Ma Present

7 G. Hewitt. The genetic legacy of the Quaternary ice ages. Nature, 405:907–913, 2000. Phylogenetic data: mid-high latitude Spread is a late Quaternary phenomenon

8 Age (Myr) 1 2 3 0 Alnus Quercus TreesShrubs Gradual spread of Alnus and Quercus into S America Lower amplitude fluctuations before 2 Ma Palaeoecological data: pollen from High plain of Bogotà 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.

9 The last 16 kyr in southernmost Chile 53.6ºS S. L. Fontana and K. D. Bennett. Postglacial vegetation dynamics of western Tierra del Fuego. The Holocene 22: 1337-1350, 2012. 10 ka Laguna Ballena Forest (Nothofagus) 10 ka Shrubs and herbs

10 The last 16 kyr in south-eastern Brazil 29.5ºS 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. 2.9 ka Rincão das Cabritas Forest (Nothofagus) Herbs

11 Age 14 C yr BP Latitude Timing of major vegetation change by latitude in South America ca 10 ka

12 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

13 Tertiary: hot (and wet?), stable Late Quaternary: 100-kyr oscillation superimposed from northern ice-sheets; Early Quaternary: cooling, increasing amplitude 20-kyr oscillations Present patterns result from a combination of these three layers: none is strong enough to dominate continuously All periodicities: variable amplitude climate, especially precipitation, response to orbital forcing gradual spread diversification biome shifts Quaternary response: low latitudes

14 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

15 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) Outcomes: 1. Major changes in vegetation happen unpredictably and at a wide range of times 2. Lineage splitting independent of these changes No process is strong enough to dominate

16 Conclusions: consequences The higher diversity of tropical ecosystems is because of this stability, after all What do we mean by stable climate? Equatorial climates of the Quaternary may be as stable as climate can ever be 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


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