Introduction

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 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?

3. 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.

4. 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 A. Berger. Long-term variations of caloric insolation resulting from the earth's orbital elements. Quaternary Research, 9:139-167, 1978. In phase

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

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

7. 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.

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

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

10. 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.

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

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. 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 from northern ice-sheets; biome shifts 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

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’) 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

16. 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