How invasive species threaten natural ecosystems

GS Paper III

News Excerpt: 

Recently Andaman & Nicobar Island Authorities have asked for help from the Wildlife Institute of India for controlling the population of chital (Spotted deer) in Netaji Subhash Chandra Bose Island (Ross Island).

More About The News: 

  • Chital, originally from mainland India, were brought to a minuscule island, measuring only 0.3 square kilometers, by the British during the early 20th century. With no natural predators or competitors and adept swimming abilities, chital quickly proliferated throughout the Andamans. This has highlighted the issue of invasive species and the peril they present to endemic ecosystems.

History of Invasive Biology: 

  • The study of invasive species gained prominence in the 1980s, spurred by growing environmental concerns and a lack of comprehensive scientific understanding. 
  • Charles Elton's seminal work laid the foundation for invasion biology as a distinct field of study, emphasizing the ecological ramifications of species introductions. 
  • Today, invasion biology grapples with the growing pace of biological invasions fueled by modern trade, travel, and technology. The consequences of these invasions manifest in every corner of the globe, posing significant challenges to global biodiversity conservation efforts.

About invasive alien species:

  • The Convention on Biological Diversity (CBD) defines invasive alien species (IAS) as those whose introduction and/or spread outside their natural past or present distribution poses a threat to biological diversity. These encompass animals, plants, fungi, and even microorganisms, impacting various ecosystems.
  • According to the CBD, IAS exhibit the characteristics of "arrive, survive, and thrive." This implies that they are introduced, either naturally or by human intervention, survive on local resources, reproduce rapidly, and outcompete native species for resources.
  • In India, the Wildlife Protection Act of 1972 (amended in 2022) provides a narrower legal definition of IAS. It refers to species of animals or plants not native to India, whose introduction or spread may threaten or adversely impact wildlife or its habitat. However, this definition excludes species within India that may be invasive in specific regions, such as the chital in the Andamans. Despite being protected in mainland India, chital have become problematic in the island chain.

Examples of invasive wildlife in India:

  • Red-Eared Slider: The red-eared slider, originating from North America, has become a popular exotic pet in India. However, many of these turtles are abandoned in local water bodies, where they outcompete native species for resources, prompting authorities to take action against illegal wildlife trade. Initially sighted in Andhra Pradesh during the Indian aquaculture boom of the 1990s, the red-eared slider has since colonized major rivers and water bodies across India, causing devastation to native fish populations and even preying on terrestrial and aquatic birds.
  • African Catfish: The African catfish, also known as the African sharptooth catfish, is a resilient species native to Africa and West Asia, where it thrives in various habitats ranging from lakes and rivers to swamps, agricultural canals, wells, and even drains. Its robust population is so widespread that the International Union for Conservation of Nature and Natural Resources (IUCN) has not deemed it necessary to assess its conservation status. In India, it first appeared in Andhra Pradesh during the aquaculture boom of the 1990s. Since then, it has invaded major rivers, water bodies, and wetlands across the country, decimating native fish populations. Recent studies have documented the African catfish preying on various wildlife, including small terrestrial birds, aquatic birds, and turtles, in ecological hotspots like Keoladeo National Park in Bharatpur and Periyar National Park on the Tamil Nadu-Kerala border.
  • Red-Bellied Piranhas: Red-bellied piranhas, native to freshwater rivers flowing through South American nations like Argentina, Brazil, and Venezuela, have garnered attention due to their formidable reputation. The Wildlife Institute of India, located in Dehradun, first documented the presence of piranhas near the Dowleswaram barrage in Rajahmundry last year, raising concerns about their presence and potential impact in Indian waterways.
  • Alligator Gar: Recent findings by the Jammu and Kashmir Lake Conservation and Management Authority revealed the accidental capture of an alligator gar fish during routine cleaning of Dal Lake, sparking debates about the presence of invasive species in India's water bodies.
  • Tilapia: Introduced into India to bolster food security, tilapia species like the Mozambique and Nile tilapia have spread extensively across the country's waterways, infiltrating biodiversity hotspots and posing further challenges to native ecosystems.
  • Alien Invasion Examples Beyond Borders: The phenomenon of species being introduced outside their native habitats, facilitated by human activity, extends far beyond the African catfish. Examples abound worldwide, such as the introduction of Himalayan tahr in New Zealand for sport, macaques in Florida for a film shoot, and the spread of the gulmohar tree from Mauritius to India as an ornamental plant. The introduction of the eucalyptus tree in India for social forestry schemes and its subsequent detrimental effects on water resources and soil fertility serve as a cautionary tale. Similarly, invasive species span various taxonomic groups, from microbes to plants to animals, posing significant threats to global biodiversity.

Other Examples:

  • Island ecosystems, like those of the Andaman and Nicobar Islands, face significant threats from invasive species. Over time, these islands have become home to numerous introduced plants, animals, and even viruses, disrupting native biodiversity and ecosystem dynamics.
  • One notable example is the introduction of elephants for logging purposes in the 1950s. After the timber company responsible for these elephants went bankrupt, many of these animals were set loose, leading to a feral elephant population that has since wreaked havoc on the islands' vegetation. The proliferation of feral elephants, along with other introduced species like Axis deer, has contributed to the decline of local species and habitat degradation.
  • Among the introduced bird species, only a handful, such as the common myna and house sparrow, have thrived in the Andaman and Nicobar Islands, while others have struggled to establish themselves. The common myna, in particular, has earned a spot on the International Union for Conservation of Nature's list of the 100 worst invasive species.

How do IAS impact native flora and fauna:

  • Invasive species serve as disruptors in the delicate balance of ecosystems, often causing disturbances in food chains and dominating habitats where competition is absent. 
    • Ecological Experts have emphasized that invasive species can exert significant influence over entire ecosystems, especially in the absence of natural competitors. For instance, at Keoladeo Park in Bharatpur, a UNESCO World Heritage site, the African catfish has been observed preying on water fowls and migratory birds, disrupting the park's delicate ecological balance. 
    • The proliferation of chital in the Andaman Islands has similarly impacted native vegetation regeneration, as these deer species are known to consume seeds and seedlings, hindering the natural growth cycle.
  • The ramifications of these introductions became evident as species like the dodo faced extinction due to habitat destruction caused by the arrival of new animals. Since then, numerous bird species, along with countless others, have met a similar fate, with introduced mammals being responsible for the majority of bird extinctions since 1500.
  • Australia's efforts to eradicate millions of feral cats underscore the grave threat these invaders pose to indigenous species. 
    • Similarly, New Zealand takes aggressive measures against invasive species due to the vulnerability of its endemic fauna.
  • In modern times, the exotic pet trade serves as a conduit for the spread of pathogens like West Nile Virus and Ebola, posing risks to human and animal health alike. 
    • The impact of invasive species extends beyond visible organisms to include deadly viruses that traveled alongside European explorers. Smallpox, influenza, measles, and other diseases wreaked havoc on indigenous populations in the 'New World,' highlighting the unintended consequences of global exploration.

What are IAS’ economic impact:

  • In September 2023, the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES), founded by the UN, released a comprehensive report on invasive species. The report highlighted that approximately 37,000 established alien species have been introduced worldwide, with around 200 new alien species introduced annually. 
    • The economic toll of invasive species globally exceeded $423 billion annually in 2019. These costs stem from the damage inflicted by invasive species on natural ecosystems. For instance, India's National Biodiversity Action Plan of 2019, published by the National Biodiversity Authority, pointed out the economic impact of the cotton mealy bug (Phenacoccus solenopsis), a North American invasive species that has significantly impacted cotton crops in the Deccan region, resulting in substantial yield losses.

Counter View:

  • Despite the ecological challenges posed by invasive species, some ecologists advocate for a shift away from the native-alien dichotomy. They argue that assessing organisms based on their environmental impact, rather than their origins, is essential for effective conservation and management strategies in a rapidly changing world.
  • The digital economy has also facilitated the spread of invasive species, with online platforms like eBay becoming hotspots for trading potentially invasive plants. Studies have shown that a significant number of invasive plant species are readily available for purchase online, making it easier than ever to unintentionally introduce these species to new regions.
  • This ease of access to potentially invasive species highlights the need for greater awareness and regulation in the online trade of flora and fauna. Additionally, the multimillion-dollar aquarium industry, fueled by the trade of ornamental fish, poses a significant risk of introducing invasive species into new environments.


India contends with its own array of invasive species across terrestrial, freshwater, and marine ecosystems. Introduced plants and animals, including weeds like Lantana and Parthenium, pose threats to native flora and fauna, disrupting ecosystems and impacting agriculture and forestry. Efforts to combat invasive species are hindered by inadequate management strategies and limited consensus on the scope of the problem. While various studies highlight the prevalence of invasive species in India, comprehensive measures to address the issue holistically are still lacking.

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