Relevance: GS-3: Conservation, Environmental Pollution and Degradation, Environmental Impact Assessment.

Key Phrases: Global Tiger Day, International Union for Conservation of Nature, tiger reserves, Genetics, connectivity, Inbreeding, Similipal Tiger Reserve, Ranthambore tiger reserve, National Tiger Conservation Authority (NTCA).

Why in News?

• July 29, which is Global Tiger Day (also called International Tiger Day), the world and India can celebrate the recovery of at least one endangered species.
• India is now reporting increased tiger numbers, and a recent International Union for Conservation of Nature assessment suggests that tiger numbers have increased by 40% since 2015. This is cause for celebration but the rise in tiger numbers is not enough to prevent their extinction.

Genetics and connectivity:

• Population:
  • Decades of research in ecology and evolution suggests that numbers are critical to avoid extinction.
  • Populations that are smaller than 100 breeding individuals have a high probability of extinction.
  • At the same time, for populations to persist, they should be part of larger landscapes with other such populations that are connected.
  • A closer look at the distribution of tigers across their range shows that most tiger ‘populations’ are smaller than 100.
• Genetic Drift:
  • Small and isolated populations face a high probability of extinction. This is because small populations are subject to chance/random events.
  • These chance events may cause them to lose advantageous genetic variants, while other, detrimental genetic variants might increase in frequency. This process is called genetic drift.
• Inbreeding:
  • Individuals in small populations are more likely to be related, leading to inbreeding.
  • This exposes the many slightly disadvantageous genetic variants that are present in all genomes.
  • When expressed together, these detrimental genetic variants cause inbreeding depression, and reduced survival and reproduction of inbred individuals.

Research findings

• Sets of tiger reserves that show shared genetic variation are well connected — the inference is that the intervening landscapes facilitate connectivity or movement.
• On the flip side, sets of tiger reserves that share less genetic variation must have barriers or landscapes that impede movement and connectivity.
• Case study of central India:
  • In the research scientists analysed tiger genetic samples in the central Indian tiger landscape and investigated genetic sharing between populations.
  • Most land-use types were not too bad for tiger connectivity, including agricultural fields.
  • The presence of built-up areas and high traffic roads greatly impeded tiger movement.
  • The results showed that extinction could be avoided if corridors were safeguarded.
  • Fencing tiger reserves and isolating them resulted in high extinction.
  • The models were used to predict the impact of impending development projects in central India - widening of certain highways, for instance, would make them barriers, thereby increasing extinction substantially.
  • As long as the landscapes is managed outside tiger reserves to allow tiger movement, and protect prey and tigers inside tiger reserves, tigers are sure to survive in landscapes such as central India.

Why connectivity matters?

• The similar genetic makeup of tigers in different reserves indicates that individual tigers born in one tiger reserve have moved across the landscape and bred with tigers in other reserves.
• In this way, connectivity between tiger habitats facilitates healthy genetic exchange and thus more viable tiger populations in the future.
• Extensive focus on tiger conservation and connectivity over the last decade has created a swathe of effective conservation plans for tigers in India.
• As the focus has shifted from independent protected areas to a wider landscape approach, these plans increasingly emphasize the importance of wildlife corridors to facilitate natural gene flow throughout the landscape.

What about tiger populations that are already isolated?

• Similipal Tiger Reserve:
  • The recent work on pseudo-melanistic or black tigers found in Odisha has demonstrated the genetic effects of isolation.
  • Genome sequences of a litter of zoo tigers that included pseudo-melanistic cubs revealed that a single spelling mistake (or mutation) in a specific gene causes these tigers to look this way.
  • The specific genetic variant was looked at in tiger DNA and found that it was common only in Similipal, where 60% of the tigers carried at least one copy.
  • Other analysts have suggested that the tigers in Similipal form a small and isolated population.
  • All the results pointed to genetic drift, or random events that have led to this genetic variant that causes pseudo melanistic coat colour becoming common only in Similipal.
• Ranthambore tiger reserve:
  • In Rajasthan, genome sequences from wild tigers reveal that individual in the Ranthambore tiger reserve show inbreeding.
  • There are no adverse effects of inbreeding as of yet, individuals are related and carry potentially disadvantageous genetic variants, which might affect the survival and the reproduction of tigers in Ranthambore in future.

Way Forward:

• While India celebrates the recovery of tiger populations only by looking at numbers, it must not lose sight of other factors that are critical to their continued survival, such as connectivity.
• Special attention is needed for populations that are becoming isolated and facing the genetic consequences of such isolation.
• The future of such populations may depend on genetic rescue or even the introduction of novel genetic variants.
• The novel genome sequencing technology provides an opportunity to understand tigers much better in the context of their conservation.
• The future of tigers will require a ‘dialogue’ between such data and management strategies in order to ensure their survival.
• India is lucky to have so many wild tigers and it must work together to save them.

Source: The Hindu

Mains Question:

Q. How can increased habitat connectivity for tigers lead to more resilient tiger populations in the future? Critically examine.