How invasive species threaten natural ecosystems

Over the past two decades, studies have examined the seemingly innocuous herbivores’ deleterious impact on the islands’ native flora and fauna — bringing to spotlight the topic of invasive species, and the threat they pose to endemic ecosystems.

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.” Crucially, 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 favourite 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. Specimens are, thus, routinely seized by authorities as a measure to thwart illegal trade of wildlife. Last June, the Customs Air Intelligence Unit seized 6,850 live red-eared sliders from two passengers at the Trichy International Airport.

With regards to species of fish, many were introduced in India to feed the demand for those maintaining aquariums. For instance, 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 system of India including the mighty rivers like Ganga, Yamuna, Sutlej, Godavari, Periyar River and the lakes like Vembanad Lake,” a 2019 study by the National Biodiversity Authority stated.

How do IAS impact native flora and fauna?

K Sivakumar, a professor in the Department of Ecology and Environmental Sciences, Pondicherry University, said that 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, he added.

For instance, “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,” Professor Sivakumar said.

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 are 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. The report showed that around 37,000 established alien species were introduced worldwide, with roughly 200 new alien species introduced each year.

Along with causing dramatic changes to biodiversity and ecosystems, the global economic cost of IAS was over $423 billion annually in 2019. These costs arise out of the damage IAS inflict on an area’s natural ecosystem

For example, 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.