Model Answer
0 min readIntroduction
The Indian subcontinent’s biodiversity is characterized by a complex mosaic of flora and fauna, often exhibiting discontinuous distributions. The ‘Satpura hypothesis’, proposed by Sidney Dillon Ripley in the 1950s, attempts to explain these biogeographical patterns. This hypothesis posits that the geological history of the Indian subcontinent, particularly the rise of the Satpura range and other associated geological features, played a crucial role in isolating and differentiating populations, ultimately leading to the present-day distribution of several species. Understanding this hypothesis is vital for comprehending the evolutionary history and conservation challenges facing Indian biodiversity.
The Satpura Hypothesis: A Detailed Explanation
The Satpura hypothesis, initially formulated based on avian distribution, suggests that the Satpura range, along with the Vindhya and Aravalli ranges, acted as significant biogeographical barriers. These ranges, formed during the Precambrian and Paleozoic eras, created a series of isolated habitats, preventing gene flow between populations and fostering allopatric speciation. The hypothesis doesn’t solely focus on the Satpura range itself, but rather the broader geological landscape it represents.
Geological Context and Barrier Formation
The Indian subcontinent experienced significant geological upheaval during its formation. The collision of the Indian plate with the Eurasian plate led to the uplift of the Himalayas and the formation of associated ranges like the Satpuras. These ranges created a north-south divide, influencing drainage patterns and creating distinct climatic zones. Specifically:
- The Satpura Range: Acts as a barrier to the movement of species between the Gangetic plains and the Deccan plateau.
- The Vindhya Range: Further south, it reinforces the barrier effect, separating the Gangetic plains from the Central Indian forests.
- The Aravalli Range: Though older and more eroded, it still influences species distribution in western India.
- River Systems: Major rivers like the Narmada and Godavari, flowing through these ranges, also acted as corridors and barriers depending on their course and seasonal fluctuations.
Discontinuous Distribution of Species: Examples
Several species exhibit discontinuous distributions that can be explained by the Satpura hypothesis. These include:
- Malabar Grey Hornbill (Ocyceros griseorhinus): Found in the Western Ghats and the Eastern Ghats, with a significant gap in distribution across the Deccan plateau, likely due to the Satpura barrier.
- Nilgiri Tahr (Nilgiri tragulus hircus): Restricted to the hills of the Western Ghats and the Nilgiri Hills, with no presence in the central Indian highlands, again suggesting a barrier to dispersal.
- Indian Leopard (Panthera pardus fusca): While widely distributed, certain subspecies show fragmented populations, potentially influenced by the geological barriers.
- Certain plant species: Many plant species endemic to the Western Ghats have no corresponding populations in the Eastern Ghats, and vice versa, indicating limited dispersal across the Deccan plateau.
Corridors and Refugia
The hypothesis also acknowledges the existence of corridors that allowed for some degree of species movement. These corridors were often associated with river valleys and lower elevation passes through the ranges. During periods of climatic change, such as glacial cycles, these ranges also served as refugia, allowing species to survive in isolated pockets. The Narmada valley, for instance, acted as a potential corridor for species movement between the Western and Eastern Ghats.
Limitations and Modern Perspectives
While influential, the Satpura hypothesis isn’t without its limitations. Modern biogeographical studies incorporate factors like climate change, habitat fragmentation due to human activities, and long-distance dispersal mechanisms. Genetic studies have revealed more complex patterns of species relationships than initially predicted by the hypothesis. However, the geological framework provided by the Satpura hypothesis remains a crucial foundation for understanding the biogeography of the Indian subcontinent.
Conclusion
The Satpura hypothesis provides a valuable framework for understanding the discontinuous distribution of species in the Indian subcontinent. While modern biogeographical research incorporates additional factors, the geological barriers created by the Satpura and associated ranges undoubtedly played a significant role in shaping the evolutionary history and present-day biodiversity of the region. Conservation efforts must consider these historical biogeographical patterns to effectively protect and manage India’s unique flora and fauna, particularly in the face of increasing habitat fragmentation and climate change.
Answer Length
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