Alien Species

Invasive Alien Species
Invasive Alien Species

Alien Species are non-native or exotic organisms that are found away from their natural distribution areas. Alien species are sometimes introduced to meet the needs of farming and forestry systems. However in certain cases the alien species become invasive. Invasive alien species are defined as non-native species that spread rampantly in a new ecosystem and have adverse effect on local biodiversity. These species can cause harm to local plants, animals and may even harm human beings. Invasive alien species are considered one of the major threats to biodiversity and they can produce fertile offspring in large numbers thereby disrupting the natural balance of native species. As per IUCN- ‘Alien Invasive Species are alien species that become established in natural are semi-natural ecosystems, an agent of change and ultimately pose threat to the native biological diversity’. Invasion follows a pattern- first, a species gets transported to a new habitat. Second, it successfully reproduces to establish a base population. Third, it gets naturalized in the new surrounding thereby causing population explosion of species. Human activities like trade, tourism, transport etc. are the primary reasons for introduction of alien species. Certain invasive species in India are Lantana, Parthenium, Eupatorium, Blue gum chalcid wasp (Leptocybe invasa), Amazon Sailfin Catfish, etc.

History of Invasive Alien Species and their spread

The history of introduction of alien species can be traced back to centuries. Though it cannot be ascertained when exactly exotic species were introduced in India, but, since the 1800s we can find various records of such introductions. There are various reasons that can be attributed to this, ranging from curiosity to ornamental and commercial purposes. Primarily during the British era, number of alien species were introduced in India, many of which have become invasive. During 1809-10, Britishers introduced Latana Camara (native of tropical America) in India as an ornamental shrub. Known as the worst weed across the world, it has then spread over northern and southern parts of India. Human activities like construction, deforestation, etc. have contributed in its fast spread. Prosopis, a theory tree from South America was introduced around 1870 as a fuel wood source due to its extreme drought tolerance. During the Second World War, Siam weed was brought into southern India from Indonesia and Burma by soldiers moving from Assam to Kerala. Also, mile-a-minute (Mikania Micrantha) weed which has a rapid growth rate of about 20-30cm per day was brought into Assam during the war as it would help in quickly covering and hiding airstrips.

In 1900s spotted deer was introduced in Andaman Islands and placing the species under most protection worthy list of animals under schedule-1 of wildlife law has contributed to its rapid spread. Another reason which led to an alien species introduction was wheat import during famine of 1950s. Parthenium hysterophorus entered India during the import and was seen during 1955 in Pune after which it spread. During 1900s a few other species entered India like serpentine leaf miner through imported chrysanthemum cuttings, spiralling whitefly which came from Sri Lanka. Similarly, in 1991, the coffee berry borer pest came into India along with Tamil migrants from Sri Lanka.

Besides this, introduction of wattle from Australia tannin in the Nilgiris also caused encroachment in the Shola Forests. India imported a pair of Giant African Snail from Mauritius out of curiosity to study it. This has now spread in vast numbers. Further species like Brown Trout, Mozambique Tilapia, African Catfish, etc. were introduced for various purposes like sports, aquaculture, etc. Lastly, lack of proper laws which aids illegal import and trade of alien species also has led to introduction of alien invasive species. Such species (arapima, alligator gar) can be seen in large numbers in areas like Kerala’s wetlands where during floods, illegally farmed invasive exotic species escape and enter nearby wetlands and then spread uncontrollably.

Impacts of Invasive Species and Threat They Pose

Invasive alien species (IAS) have several long-term and devastating effects on the natural eco-system. As per government data, domination of invasive species in the Western Ghats was as high as 70% and places where these tree species were found, no fresh growth of indigenous plants occurred. This in turn adversely affected the local animals like elephants who faced shortage of their food. Also, vast eucalyptus and wattle expanse have started effecting the natural Shola Forest which is the original habitat of Nilgiri Tahr. Similarly, Kodaikanal town in Tamil Nadu has been witnessing frequent Indian Bison visits who wander about in search of food.  This leads to an increase in man animal conflict causes death of native animals. The Toda livestock of Nilgiris has also reduced due to conversion of once an undulating grassy plateau into woody and thorny grasslands as an invasion of wattle.

Species like Lantana and Chromolaena have taken over vast areas in major biodiversity hotspots like Western Ghats and Eastern Himalayas. Such species have hindered the growth of native species and have upset the ecological balance weeds and other unwanted species also inhibit growth of agricultural crops thereby reducing crop yield. These weeds also damage soil quality and fertility therefore making harvesting difficult. Weeds spread to water canals and impede flow of water, hamper navigation. They also pollute the water hence causing death to fish and affecting traditional fisheries.

The unwanted invasion has forced people to look for new livelihood opportunities in semi-arid states of Rajasthan, Gujarat, Karnataka, Andhra Pradesh, etc. Certain alien species release toxins and resin like substances that are harmful for microorganisms and also affect food of herbivores. Reports have indicated that due to invasive fishes, diversity of freshwater fishes has been reducing at an alarming pace. One such example of invasive fish is the Amazon Sailfin Catfish that besides degrading native fishes of Vandiyur Lake also affect environment after death as they lack commercial value and hence are dumped and also, they are not scavenged by other birds and animals. The floristic diversity of important forest areas like Kanger Valley Forest area, Karlapat Wildlife Sanctuary, Sunderban National Park, Bhitarkanika National Park, Phulbani Forest, etc. also has reduced. The Mangrove ecosystem have also been deteriorated due to invasion. Invasive species have also affected the natural pollination process by cross-contamination of pollen grains.

Apart from these effects, the certain alien invasive species have been known to spread diseases. The Parthenium weed is noxious and causes some nerve disorders. It also is harmful for asthmatic people. These weeds cause dermatitis in rodents like rabbits. Lastly the invasive species have huge impact on the economy. In 2001, economists pegged yearly loss in agriculture and forestry at around 90 billion dollars due to damage caused by invasive species. This huge figure is without even taking into account the costs incurred on species management and control. Similarly, Kerala suffers a loss of about 200 crores per year due to coconut mite. Further, invasive plants threaten food and fibre production whose economic costs are yet another loss. Besides due to irretrievable loss of native species, it becomes a grave matter of concern to control and eradicate these invasive alien species. The Convention on Biological Diversity, 1992 has even recognised invasive alien species as the second biggest threat to biodiversity next to habitat destruction.

Global and India Scenario of Invasive Alien Species

India is not the only country to be troubled by IAS. IAS has spread all over the world effecting almost all nations. In Australia, decades ago yellow crazy ant got introduced. It remained inactive for a long time, however, during 1990s its population exploded and by 2003 it had colonised about 2000 hectares of tropical forest causing loss of native insects, birds, reptiles, etc. The spread has turned the once abundant red crabs into decimated species and has almost turned certain forest into dead wood. Many countries have been facing the negative effects of spread of eucalyptus and Australian Melluca that exudates chemical which inhibits growth of other species. Similarly, a species that is Ageratum Conyzoides has invaded several South Asian nations including India. An USA based study      indicates that over 1,30,000 alien species of plants, animals and microbes have been reportedly become invasive in just 6 nations- UAS, UK, Australia, South Africa, India, Brazil. This indicates about 5 lakh alien species have been introduced into ecosystems all over the world.

Different nations have adopted different strategies to deal with this menace. New Zealand and Australia have put in place strict and tight quarantine regulations with rigorous monitoring. When Parthenium spread was reported in western Australia, the authorities put a check on traffic and cattle movement with setting up several vehicle wash checkpoints to stop further spread. Other methods like use of biological control agents have also been used like in case of USA- Australian Vedalia Lady bettle was brought to control the cottony cushion scale insects, in India- Dactylopius opuntiae was used to control prickly pear, in Hawaii Islands- predatory snail Egulandina Rosea was introduced to check alien species that is African giant snail. In India, the Australian ladybird bettle is also used as a biological control agent and it uses about 26 bio-control agents. Besides this in India innovative techniques of alternate use of weeds have also been seen like among Kurubas (group of people of a village in Tamil Nadu) use of Lantana and different other weed species like azima etc. for weaving baskets.

Conventions, Legislations in place

All nations are aware of the ill effects of IAS and have been striving hard to curb its menace. In1993, the international convention on Biological Diversity (CBD) was formed to ensure sustainable growth of biodiversity. During 13th meet of conference of parties (COP), the National Biodiversity Strategies and action plans (NBSAP) of CBD were revised based on Aichi Targets formed as per capacities of nation. India adopted Aichi target 9 as per which it has to identify invasive alien species along with their mode of introduction and to develop methods to manage IAS by 2020. Recognising the eminent threat posed by IAS, The Asia Pacific Forestry Commission (APFC) launched the ‘Asia Pacific Forest Invasive Species Network’ during 2004 with primary objectives of exchanging information on forest invasive species, achieve a coordinated and cooperative action plan to deal with forest invasive species and to raise awareness regarding related issues. Along the lines of this, in 2009 The Indian Council for Forestry Research and Education setup a ‘Forest Invasive Species Cell’ in order to develop management skills for invasive species.

India has certain rules and regulations in place to deal with IAS like ‘the plant Quarantine (Regulation of Import into India) order 2003 (having a mandatory pest risk analysis for products), Livestock importation Act 1898, Environment Protection Act 1986, Biological Diversity Act 2003’. These acts and orders lay the guidelines acting on which the ministry of environment, forests and climate change, National Bureau of Plant Genetic Resources, Ministry of Agriculture, etc. take necessary actions to deal with IAS and ensure its efficient management. India has a well-established quarantine system which is overlooked by above mentioned ministries. Further with increase in incidences of gene modifications and modified species, the national genetic resource centre functions proactively to monitor different species. The government has also adopted steps like banning of eucalyptus from forests of Nilgiris, removal of eucalyptus from forests of Nilgiris and Kodaikanal, removal of Prosopis Juliflora and Lantana Camara etc.


IAS pose grave threat to the native ecosystem also they have direct or indirect adverse effects on human beings. There has been increase in awareness among nations on this issue and steps are being adopted to control it. However in case of India, it needs to boost its efforts India has a dismal of number of staff dedicated towards this field. Also fragmented and individual steps of different institutions will not help to achieve long term goals. Further there is need for more financial investment in this area with a holistic, stringent and well-planned framework in order to manage IAS menace.

Government should focus on intensive and case specific approaches, instead of random steps to curb spread of IAS. Also there is need to further increase awareness among people regarding ill effects of IAS and government should encourage community participation from native areas to manage the issue. Lastly, India can adopt techniques and use ideas that have proven to be successful in nations like USA, Australia, New Zealand, etc. IAS are detrimental and are capable of causing irreversible damage to the ecosystem and it must be treated seriously, and urgent actions need to be taken to stop any further damage.



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