“Tyger! Tyger! Burning Bright
In the forests of the night
What immortal hand or eye
Could frame thy fearful symmetry?”
– William Blake(1794)
Of all the big cats, or perhaps of all the endangered species, the Tiger may be both the most charismatic and the most feared, as phrased in the timeless poem by William Blake.
Its ancestral roots and history are depicted in its phylogeography, the genetic patterns of diversification among individuals and populations on both temporal and geographical scales.
DNA evidence shows that all of the 37 living cat species trace back to a Panther-Like Predator that lived in South East Asia in the late Miocene over 11 million years ago (MYA). The radiation of modern felids began with the divergence of the ‘Panthera’ lineage from the ancestral cat species around 10.8 million years ago. A few million years later, this lineage diverged into the ancestral species of two groups, one consisting of two species of Clouded Leopards and other encompassing the ‘Great Roaring Cats’ of the Panthera genus- The Lion ( Panthera leo), Jaguar ( Panthera onca), Snow Leopard ( Panthera uncia) , Leopard (Panthera pardus) and Tiger (Panthera tigris). The split of the Panthera lineage was followed by a rapid series of divergence and migration events that led to the five extant Panthera species. The Asian derived Panthera species subsequently spread into America (Jaguar), Africa (Lion and Leopard) and others remained in Asia (Tiger, Snow Leopard and Clouded Leopard).
In historic times, Tigers were found all the way from temperate zone forests of the Russian Far East to the tropical forests of south western India. They ranged from Azerbaijan and Iraq on the west all way through the Indian subcontinent to parts of Southern China, eastern Russia and Southeast Asia. Their range covered 30 present day countries, stretching over 70 degrees of latitude and 100 degrees of longitude on the Earth’s surface. The oldest Tiger fossils were found from Northern China and Java. By the late Pliocene and early Pleistocene, Tigers were widely distributed in Eastern Asia.
ENTERING THE INDIAN SUBCONTINENT:-
The pattern of genetic variation in the Bengal Tigers corresponds to the premise that the Tigers arrived in India approximately 12,000 years ago, after being forced to spread southwards in search of suitable habitat as successive Pleistocene glacial and other geological events made Northern Asia inhospitable. This recent history of tigers in the Indian subcontinent is consistent with the lack of tiger fossils from India prior to the late Pleistocene and the absence of Tigers from Sri Lanka which was separated from the subcontinent by rising sea levels in the early Holocene.Tigers once overlapped with lions in a wide region stretching across North West India. Early human modifications of landscapes and extirpation of the more easily hunted lions by human societies might have benefitted Tigers, allowing them to expand their range in drier regions of North- West India by moving into newly opened ecological niches.
India has three distinct and genetically connected Tiger populations. These are in South India, Central India, the Terai and North- east India including the Sundarbans and in Ranthambore. The Big Cats cope with the heat of Rajasthan, the wetness of the Western Ghats and the North – Eastern India, the open terrain of the Terai and the tidal mangroves of the Sundarbans.
A case study has been presented here focusing the demographic history and uniqueness of Ranthambore and Sundarbans.
About 6000 years ago (in the mid-Holocene), the shoreline of the North-eastern Indian Peninsula was situated to the west of the present shoreline which was comparatively closer to the foothills of the Himalaya. Therefore, the present Sundarban area did not exist for terrestrial life until the shoreline had moved eastward, and Tigers could arrive from Peninsular India. “In 1756, when Siraj-ud-Daulah recaptured the City of Kolkata (then Calcutta) from the British, today’s Salt-Lake area used to be the main city and the Lower South Circular Road that’s now known as Chowringhee used to be the city’s southern border. Beyond that were the forests of Sundarbans and there are beliefs that tigers were often sighted in those forests which now house busy localities like Tollygunge and Behala.” A shift in the river Ganges brought changes to agricultural land use in the areas adjoining Sundarbans. After that the anthropogenic activities from 600 to 800 years ago started to impact the Tiger habitat. All these factors probably caused the complete isolation of Sundarban Tigers.
Picture 1: Sunderbans Tigress (Picture Credit: Niladri Kundu)
Sundarbans Tiger Population is an isolated, genetically and ecologically differentiated group of the Bengal Tiger. The Sundarban Tigers need overarching conservation in order to preserve their unique morphological adaptations and genetic uniqueness for the future.
Ranthambore in Rajasthan is arguably India’s most well-known Tiger Reserve. A genetic study suggests that Ranthambore’s Tigers suffer from low genetic diversity and isolation. While the reserve itself is doing well in terms of Tiger numbers, it is cut off from other forests. Geographically, Ranthambore is poorly connected to other tiger conservation landscapes. Historically, tigers extended further northwest of Ranthambore into Pakistan, but went locally extinct in the early 1900s. Genetic data reveal that northwest Tigers and these extinct populations were connected to other tiger populations in the past. Together, this makes Ranthambore the western-most extant population of wild tigers today.
Picture 2: T13 from Ranthambore (Picture Credit: Suddhasattwa Das)
Securing Corridors for Tiger Movement:
The climatic changes that shaped the expansion of tiger range across Asia during the Pleistocene and Holocene primarily operated through changes in connectivity of Land- bridges and landscapes, which in turn was driven by changes in sea level and vegetation patterns. These environmental factors led to the evolution and radiation of large ungulates, particularly several species of deer and wild cattle, opening up an ecological niche for a large, solitary, forest predator. As tigers have good dispersal abilities and connecting corridors assist their movements between subpopulations, maintenance of this connectivity is crucial. Ecological and anthropogenic factors are known to change the genetic structure of the population even in contiguous habitats.
Though conservation efforts – from protected reserves to endeavors to mitigate human-tiger conflict- are currently in place, researchers state that- “it is critical to maintain within-population variation, as well as increasing population connectivity on a large scale.” It was found that 93% of the tiger DNA variants from the historical period (1858-1947) are no longer present in the current Tiger population. This is due to loss of habitat and habitat fragmentation, meaning lower population sizes, and the prevention of tigers from dispersing as they once would have, which means their gene pool is no longer mixing across the subcontinent.
The tiger story is built around a narrative of numbers. Undoubtedly, numbers are important. They indicate a continuous protection effort and that the habitat is doing well. But numbers are the beginning of the Tiger story, not the end. An effort to link reserves would need more stakeholders and political will. This is not easily done as said, but needs to be attempted as a conservation priority. Apart from moving tigers with human intervention, the corridor needs to be strengthened too.
Forests in this landscape already carry a different protection status, but corridors in between them are given the least conservation priority and are vulnerable to human activities. As these forests are located within a human- dominated, tiger hostile landscape, it is very important that the corridors between the forests are better protected so as to ensure tiger movements and long term survival of tigers in this landscape. Despite major conservation initiatives, the last 10-15 years have witnessed more than 40% decline in the estimated area known to be occupied by Tigers, and the current range is only 7% of its historic range. Tigers can only persist as part of larger populations that extend into surrounding forests. Conservation of Tigers therefore requires a joint management of protected areas and the greater landscapes.
Tiger conservation is a rallying cry: because a tiger is an apex predator, you cannot preserve it in the wild without preserving its environment.
Let the spirit of the Yellow- Stripes never die!!!!
1. Singh, Sujeet Kumar, “Conservation genetics of the Bengal Tiger (Panthera tigris tigris)in India.”
2. K. Ullas Karanth, “Tiger Ecology and Conservation in the Indian Subcontinent.” : Journal of the Bombay Natural History Society.
3. “Conservation priorities for endangered Indian Tigers through a genomic lens.” : Meghana Natesh, Uma Radhakrishnan ; Scientific Reports 7, Article Number: 9614 (2017).
About the Author
Diptarka Ghosh, a Post Graduate in Zoology from the University of Calcutta, is currently pursuing research in the Zoological Survey of India. An avid Nature and Wildlife lover, he is interested in working for wildlife conservation in the near future.