How invasive species threaten natural ecosystems

Subject: Environment

Section: Species in news

Context:

In a bid to manage the teeming population of chital (spotted deer) in Ross Island (officially known as the Netaji Subhash Chandra Bose Island), the Andaman and Nicobar Islands administration recently sought help from the Wildlife Institute of India.

More on news:

Chital, native to mainland India, were introduced to the tiny island (0.3 sq km small) by the British in the early 20th century.
Having no natural predators or competitors, and being good swimmers, chital swiftly spread across the Andamans.

What are invasive alien species?

The Convention on Biological Diversity (CBD) defines invasive alien species (IAS) as “species whose introduction and/or spread outside their natural past or present distribution threatens biological diversity”.
These include animals, plants, fungi, and even microorganisms, and can influence all kinds of ecosystems.
The CBD, the United Nations’ global treaty on safeguarding biological diversity, sums up characteristics of IAS as follows: “arrive, survive and thrive.”
This means that these species need an introduction either through natural or human intervention, survive on native food resources, reproduce at a fast rate, and edge out native species in the competition over resources.
In India, the legal definition of IAS under the Wildlife Protection Act, 1972 (amended in 2022), is narrower.
They are defined as species of animal or plant which is not native to India, and whose introduction or spread may threaten or adversely impact wildlife or its habitat.
This leaves out species within India which might be invasive to a particular region — like the chital in Andamans, which are protected in mainland India, but have become a menace in the island chain.

What are some examples of invasive wildlife in India?

The list of invasive wildlife in India is dominated by certain species of fish such as the African catfish, Nile tilapia, red-bellied piranha, and alligator gar, and turtle species such as the red-eared slider.
The red-eared slider, for instance, is a favorite among India’s exotic pet owners, and many have been abandoned in local water bodies.
This turtle, native to North America, notoriously edges out local freshwater species, owing to its fast rates of reproduction, and the following competition for food.
The African catfish was brought over from Bangladesh specifically for aquaculture purposes.
The occurrence of C gariepinus (the species’ scientific name) has been reported from several inland systems of India including the mighty rivers like Ganga, Yamuna, Sutlej, Godavari, Periyar River and the lakes like Vembanad Lake.

How do IAS impact native flora and fauna?

Invasive species act as disruptors in the food chain and disturb the balance of the ecosystem.
In habitats where there is no competition, invasive species can dominate the entire ecosystem.
In Keoladeo Park, Bharatpur in Rajasthan, which is a UNESCO World Heritage site, the African catfish has been known to prey on water fowls and migratory birds as well.
Studies have shown that the proliferation of chital in the Andamans has affected the regeneration of native vegetation, as the deer are known to consume seeds and seedlings.

What is the IAS’ economic impact?

In September 2023, the UN-founded Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) brought out an exhaustive report on invasive species.
As per India’s National Biodiversity Action Plan of 2019, published by the National Biodiversity Authority, the cotton mealy bug (Phenacoccus solenopsis) is an invasive species native to North America, which has severely affected cotton crops in the Deccan, leading to yield losses.