Climate Change and the Migration of a Pastoralist People c. 3500 cal. Years BP Inferred from Palaeofire and Lipid Biomarker Records in the Montane Western Ghats, India

ABSTRACT

Human migration in response to past climate change has been recorded globally. The pastoralist Todas are believed to have colonised the higher elevations (>2000 m asl) of the Nilgiris, Western Ghats, India, after ∼2000 cal. yr BP. During the late Quaternary, climate-induced vegetation shifts in tropical montane forest-grassland mosaic of the Nilgiris have been well-documented using stable carbon isotopes and pollen, but there have been no corresponding investigations of human activity. We used several proxies to infer the human ecology of this region. Radiocarbon-dated (∼22,000 cal. yr BP to the present) peat from Sandynallah (2200 m asl) was used to reconstruct fire history, animal abundance, and human presence since the Last Glacial Maximum (LGM). While macro-charcoal records fires at the LGM, macro- and micro-charcoal indicate intense fire at ∼3500 cal. yr BP, coprophilous fungal spores indicate abundant herbivorous mammals, n-alkane signatures point to arid grassland vegetation, and steroid biomarkers show human faecal remains for the first time. We infer that a pastoralist people, most likely the Todas, migrated to the montane Nilgiris along with their buffaloes in response to prolonged or abrupt climate change in peninsular India ∼3500 cal yr BP or ~1500 years prior to what historical accounts assume.

KEYWORDS:

• Palaeoclimate
• Holocene
• human migration
• Toda
• buffalo culture
• lipid biomarker

Acknowledgements

RS was a JC Bose National Fellow during the tenure of this study. DG thanks DST INSPIRE Faculty Funds (grant no. DST/INSPIRE/04/2015/002362) for lipid biomarker analysis. SPK thanks Indian Institute of Science, Bangalore, and Inspire DST for the MS fellowship. We all thank Dr. Anupama Krishnamurthy, Mr. Prasad S, and Mr. Orukaimani of French Institute, Puducherry (IFP) who provided support and guidance in pollen slide preparation and valuable insights for the project. Sample preparation and the counting of pollen were done using both the expertise at IFP and the Thanikamoni pollen slide collection at IFP. PRB thanks Prof. Iyue, Tamil Nadu Veterinary and Animal Sciences University (TANUVAS) and the staff at Sheep Breeding Research Station (SBRS), Sandynallah, for permission and assistance with sample collection. Authors are thankful to IUAC for extending graphitisation laboratory and AMS measurement facility for ¹⁴C established under Ministry of Earth Science (MoES), Govt of India funded project with ref. no. MoES/16/07/11(i)-RDEAS.

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by DST INSPIRE [grant number DST/INSPIRE/04/2015/002362].

Notes on contributors

Sarath Pullyottum Kavil

Sarath Pullyottum Kavil is currently a PhD student at Sorbonne University, Paris. He did his MSc from Indian Institute of Science, Bangalore, where he investigated changes in vegetation and climate of the past and the impact of humans with associated environmental changes in Upper Nilgiris.

Prabhakaran Ramya Bala

Prabhakaran Ramya Bala was a Research Associate at the Divecha Centre for Climate Change and a PhD candidate at the Centres for Earth and Ecological Sciences, Indian Institute of Science. Her PhD research was centred around understanding changes in paleovegetation in the upper Nilgiris, Western Ghats, and using them as proxies to interpret changes in the environment. She is a molecular biologist and geochemist by training and uses her skills in reconstructing paleoenvironments using interdisciplinary multi-proxy techniques.

Devanita Ghosh

Devanita Ghosh is a faculty of Indian Institute of Science, Bangalore and she works on biogeochemical proxies like lipid, proteins and nucleic acid biomarkers. Her key interests lie in Microbial role inorganic C metabolism and mobilization of elements.

Pankaj Kumar

Dr. Pankaj Kumar is Scientist F in Inter-University Accelerator Centre (IUAC), New Delhi. He is an accelerator physicist with research interest in geochronology and isotope research by employing accelerator mass spectrometer (AMS) and low energy mass spectrometers. At IUAC he has played a key role in the development of AMS programs for cosmogenic radionuclides 14C, 10Be and 26Al. He is an elected member of Indian National Young Academy of Science (INYAS) by INSA. He has also served as a national Core committee member of INYAS (2017-2019). He is a life member of IPA, National Academy of Science, India (NASI) and Indian Society of Particle Accelerator (ISPA).

Raman Sukumar

Raman Sukumar is honorary professor at the Indian Institute of Science. His research interests and publications over four decades have covered the fields of wildlife ecology, conservation biology, tropical forest ecology and climate change. His work on climate change include investigations on the late Quaternary climate and vegetation in the montane Western Ghats, dendrochronological studies in the Himalaya, and climate-tree interactions in tropical dry forests. He has contributed extensively to the work of the Intergovernmental Panel on Climate Change (IPCC).