Alien invasion

Published : Jul 03, 2009 00:00 IST

MIKANIA MICRANTHA, ONE of the most prominent invasive aliens in India.-

MIKANIA MICRANTHA, ONE of the most prominent invasive aliens in India.-

BIODIVERSITY is the source of all ecological goods and services that constitute the source of living of all. India is not only gifted with geographical, climatic, cultural and social diversity but is also endowed enormously with biological diversity. The country is among the 12 mega gene centres of the world, and two of the 31 global hot spots of biodiversity (the North-eastern Himalayas and the Western Ghats) occur in this region. About 8 per cent of all the estimated species on the earth exist in India though it occupies only 2.4 per cent of the worlds land area. Among the existing biota, nearly 91,000 species of animals, 45,500 species of plants and 5,650 microbial species have already been documented in Indias 10 biogeographic regions. It is estimated that nearly 40 per cent of these are aliens, and 25 per cent of them have become invasive.

The diverse agricultural systems, employing both traditional and modern systems of cultivation, utilise thousands of locally adapted as well as bred crop varieties and nearly 140 native breeds of livestock. The country is recognised as one of the eight Vavilovian Centres of origin and diversity of crop plants, having more than 300 wild ancestors and close relatives of cultivated plants still growing and evolving under natural conditions. About 168 domesticated species of crops (including 25 major and minor crop species) have originated and/or developed diversity in this part of the world. Indigenous medical systems utilise nearly 6,500 native plants for both human and animal health care. Indias diverse preponderance of native tribal and ethnic groups has contributed significantly to the conservation and diversification of biodiversity.

In December 2000, the United Nations General Assembly adopted May 22 as the International Day for Biological Diversity (IDB), to commemorate the adoption of the text of the Convention on Biological Diversity (CBD) on that day in 1992, in Nairobi. Since 2001, the day is celebrated with a central theme. The theme for the IDB in 2009 was Biodiversity and Invasive Alien Species (IAS).

In India, the National Biodiversity Authority, established under the Biological Diversity Act, 2002, under the aegis of the Union Ministry of Environment and Forests, conducted programmes that emphasised the importance of biological biodiversity, organised outreach activities for schoolchildren, held seminars, published posters and pamphlets and staged exhibits and events designed to attract and educate the media.

Invasive alien species are species whose introduction and/or spread outside their natural habitats threatens biological diversity. They occur in all groups, including animals, plants, fungi, bacteria and viruses, and can affect all types of ecosystems. While a small percentage of organisms transported to new environments become invasive, the negative impact they have can be extensive and over time these additions become substantial.

A species introduction is usually vectored by human transportation and trade. If a species new habitat is similar enough to its native range, it may survive and reproduce. However, it must first subsist at low population densities, when it may be difficult for it to find mates to reproduce. For a species to become invasive, it must successfully out-compete native organisms, spread through its new environment, increase in population and harm ecosystems in its introduced range. To summarise, for an alien species to become invasive, it must arrive, survive and thrive.

On April 27, 2009, news about the outbreak of swine flu in Mexico caught the attention of people all over the world. In spite of unprecedented measures to check its spread, the swine flu virus managed to sneak into more than 30 countries, including India, and within weeks it had infected nearly 5,000 people all over the world.

The swine flu has, once again, reminded us about our vulnerability to invasive aliens, which do not respect geographical boundaries. Sometimes they manifest themselves as bird flu and at other times as foot-and-mouth disease and mad cow disease and lead to massive destruction of livestock populations all over the world. But human beings, birds and cattle are not the only targets of invasive alien species. Over the years, the biggest casualty of such species has been our rich biodiversity, and they have emerged as one of the greatest threats to food security. Be it mountains, plains, deserts, rivers or seas, there is no ecosystem in the country that does not reel under the impact of invasive aliens.

The common characteristics of IAS include rapid reproduction and growth, high dispersal ability, phenotypic plasticity (ability to adapt physiologically to new conditions), and the ability to survive on various food types and in a wide range of environmental conditions. A good predictor of invasiveness is whether a species has successfully invaded elsewhere.

Increasing travel, trade and tourism, associated with globalisation and expansion of the human population, have facilitated both intentional and unintentional movement of species beyond natural biogeographical barriers, and many of these alien species have become invasive. IAS is considered to be one of the main direct drivers of biodiversity loss at the global level. These species can be expected to cause substantial environmental and economic damage, and their negative effects are exacerbated by climate change, pollution, habitat loss and human-induced disturbance. Increasing domination by a few invasive species increases global homogenisation of biodiversity, reducing local diversity and distinctiveness.

Invasive alien species can directly affect human health. Infectious diseases are often traced to IAS imported by travellers or vectored by exotic species of birds, rodents and insects. IAS also have indirect health effects on humans as a result of the use of pesticides and herbicides, which pollute water and soil.

They may look harmless but are dangerous, mainly causing flu, allergies, respiratory disorders and even infertility among humans and animals. In economic terms, the cost of IAS is significant. The total annual cost, including losses to crops, pastures and forests, and in terms of environmental damage and control costs, has been conservatively estimated to be hundreds of billions of dollars, possibly more than one trillion dollars.

Manifesting themselves as microorganisms, plants, animals and fungi, these invasive alien species are notorious for their rapid reproduction and high dispersal ability. Recently, a new strain of the stem rust virus, called Ug99, has been invading wheat, leading to the loss of almost the entire crop, in many African countries including Kenya, Ethiopia and Tanzania. It has been spotted in Iran and is believed to be heading towards countries in South Asia. It may spell doom for the food security of the region because all wheat varieties cultivated in Asia are susceptible to Ug99. As one of the megadiversity countries in the world, India is particularly vulnerable to invasions by alien species.

The invasive alien often proves difficult to control. Through their uncontrolled and rapid growth, they out-compete more useful native species and leave them on the brink of extinction. Lantana is now considered one of the 10 notorious weeds in the world. A native of Central and South America, lantana came to India as an ornamental plant in 1807, when the British introduced it into the Calcutta Botanical Garden. Since then it has occupied over one lakh hectares of land in the country and proved to be a bane of0 cash crops such as coffee, cotton, oil palm and coconut. However, it is the hilly regions of the country that have largely borne the brunt of the attack.

The parthenium may not be as attractive as the lantana, but there is hardly any invasive alien species in the world that can match its dispersal ability and devastation capacity. Believed to have entered the country in the 1950s along with the supply of P.L. 480 (Public Law 480 food aid programme) wheat from the United States, parthenium now occupies 50 lakh hectares in the country and has become a major health hazard for people and animals. Other than occupying wasteland, roadsides, and railway tracks, it has colonised public parks, residential colonies and orchards.

Other prominent ones include mikania (mile a minute), which was introduced in India during the Second World War to help soldiers camouflage themselves. Now a major threat in many parts of the country, it grows 8 to 9 cm a day and muzzles small plants and chokes larger trees such as coconut and oil palm.

Eupatorium was introduced as an ornamental plant in the Calcutta Botanical Garden in the 1840s. Since then it has spread throughout South-East Asia. Its capacity for regeneration and prolific seed production enables it to form dense tangled bushes, which depress the growth and yield of crops such as rubber, cardamom, coffee, tea and mango.

India suffers an annual loss of Rs.20,000 crore in terms of agriculture produce owing to weed infestation. The most prominent among the weeds is Phalaris minor. It affects the wheat crop in particular and has curtailed yield by five million tonnes a year.

Prosopis juliflora was introduced in India in the last century and was thought to be a very promising species for the afforestation of dry and degraded land. But over the years, it has emerged as a noxious invader that can grow in diverse ecosystems, right from coastal areas to desert regions. Its rapid growth and dense formation enable it to wipe out other plant species in its surroundings.

Except for mikania, so far the control and eradication measures, through manual extraction, chemical spraying and biological means, have had very little impact on the growth of these invasive aliens. The release of Mexican beetles against parthenium has shown promising results, but given the fact that it occupies nearly five million hectares the use of beetles does not seem to be a feasible option.

Our fresh and marine water resources, including the corals, also face a grave threat from invasive alien species. The water hyacinth is believed to have originated in the Amazon basin, but it has become a big nuisance in Indias ponds, lakes and lagoons.

Tilapia, a freshwater fish, was first introduced into the pond ecosystem of India in 1952, and it has now been declared as invasive in 90 countries around the world. It multiplies at an extremely rapid pace, survives in all kinds of waters and eats everything, to the extent that native species are starved to death.

The challenge now is to find ways to manage the invasive aliens that are firmly entrenched in the country and, at the same time, take every possible step to prevent the entry of new aliens that may become invasive. The future of India hinges on the protection of its biodiversity. This task cannot be the responsibility of the government alone. We have to be partners in protecting this common heritage.

Invasive alien species are a global issue and dealing with this requires international cooperation and action. Preventing the international movement of IAS and their rapid detection on the borders are less costly than their control and eradication. Preventing the entry of IAS is carried out through inspections of international shipments, customs checks and quarantine regulations.

This requires collaboration among governments, economic sectors and non-governmental and international organisations. There are many international and regional binding agreements and voluntary guidelines that include regulations on IAS.

The Conference of the Parties (COP) to the CBD has recognised that there is an urgent need to address the impact of IAS, and at its fourth meeting it established IAS as a cross-cutting issue. The decision of the COP 6 meeting included the adoption of the Guiding Principles for the Prevention, Introduction and Mitigation of Impacts of Alien Species that Threaten Ecosystems, Habitats or Species. This target was subsequently endorsed by the World Summit on Sustainable Development and the U.N. General Assembly and was incorporated as a new target under the Millennium Development Goals.

Dr K. Venkataraman is Additional Director in the Marine Biological Station, Zoological Survey of India, Chennai.

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