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Kathmandu Sunday December 23, 2001 Paush 08, 2058.
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Alien invasive species : A global threat to
biodiversity
By Deependra Joshi
What do green crabs, zebra mussels, the
African tulip tree and the brown tree snake have in common? These are just a few of the
many plant and animal species whose unchecked population growth outside of their native
habitats have severely impacted native species populations, the functioning of ecosystems,
and global and local economies.
The global conservation community is bating
to find solutions to one of the major threats to biological diversity that continues
unabated with devastating consequences for the planet. Biological invasion by alien
species is now recognised as one of the major threats to native species and ecosystems,
yet awareness of the problem is alarmingly low. The effects on biodiversity are immense
and often irreversible.
AIS? Alien species are those that occur
outside their natural range. Alien species that threaten the existence of native plants
and animals or other aspects of biodiversity are termed alien invasive species. Alien
invasive species occur in all groups of plants and animals. As competitors, predators,
pathogens and parasites, they have invaded almost every type of native ecosystem, and
caused hundreds of extinctions.
Alien species have been defined as a species
that is non-native, non-indigenous, exotic or outsider to an ecosystem under
consideration. Introduction of such a species is likely to cause economic and/or
environmental loss and/or harm to human health. Any species including its seeds, eggs,
spores or other biological materials through which it is capable of multiplying and
propagating in an ecosystem other than its natural home could be an alien species. On the
contrary, the native species are those that have occurred historically with the evolution
of an ecosystem as its natural home. All native species thrive in harmony with each other
whereby natural succession and biological control mechanism within the ecosystem maintain
and sustain a natural balance of the community of species within that ecosystem. The scope
and cost of biological alien invasions are enormous in both ecological and economic terms.
Economic costs of alien invasive species run into billions of dollars each year.
Introduced pests and pathogens reduce crop and stock yields, and weeds degrade marine and
freshwater ecosystems.
Biological invasion: What
happens when a species is introduced into an ecosystem where it doesn’t occur
naturally? Are ecosystems flexible and able to cope with change, or can a new arrival have
far-reaching repercussions and do permanent damage? Will something special be lost
forever? Does it matter?
In the distant past, the earth’s
mountains and oceans represented formidable natural barriers to all but the hardiest of
species. Ecosystems evolved in relative isolation. Early human migration saw the first
intentional introduction of alien species as our ancestors attempted to satisfy physical
and social needs, but the magnitude and frequency of those early introductions were minor
compared to those associated with today’s extensive global trade and passenger
movements.
Careless behaviour leads to unintentional
introductions. So-called ‘accidents’ now account for the majority of successful
invasions. The list of "100 of the World’s Worst Invasive Alien Species"
published by IUCN - The World Conservation Union illustrates the incredible variety of
species that the ability, not just to travel in ingenious ways, but also to establish,
thrive and dominate in new places. Today, alien invasion is second only to habitat loss as
a cause of endangerment and extinction of the species.
Safeguarding the earth’s diversity is
the best way to maintain our life support system. Useful initiatives, which contribute to
better management practices and a reduced incidence of biological invasion, are being
taken by communities all over the world. Invasive alien species are now a major focus of
international conservation concern and the subject of cooperative international efforts,
such as the Global Invasive Species Programme (GISP). As awareness grows, people and their
communities are able to make informed choices that will have lasting effects on
their descendants.
AIS in Nepal: Being the
junction of the Palearctic and oriental realms of the earth and at the crossroad of six
floristic provinces of Asia, Nepal has a great geographical as well as climatic variation.
Such a wide range of natural attributes in a relatively small area has endowed Nepal with
the representation of various ecosystems and habitats. Consequently, Nepal has the natural
environment suitable for a wide variety of flora and fauna including its own floral and
faunal diversity.
Nepal’s natural resources have been
under excessive pressure due to the growing population’s demand and overdependence
over such natural resources for livelihood and subsistence farming practices. Many natural
habitats have suffered continual changes dues to enhanced human activities and land use
changes. Many agricultural crops, and together with them, many unknown weeds have been
introduced in the past 2-3 decades affecting agriculture, forest, rangeland and wetland
ecosystems. Rapid colonisation of Eupatorium species in subsequently degrading forest
ecosystems and increasing invasion of water hyacinth in the Terai wetlands and mid-hills
have posing severe threat. Often many AIS prey on, put-compete, hybridise and infect
native species thereby causing habitat deterioration, ecosystem disturbance and loss of
invaluable species impacts to the biodiversity.
Knowledge on alien species in Nepal is rather
meagre and limited. Any comprehensive study has yet to document and determine the status
of AIS in Nepal in order to understand and address the problems created by them. Nepal
Biodiversity Action Plan (draft, 2000) provides a list of alien floral species in Nepal.
However, the number of species may be more. A number of AIS has been observed in different
parts of Nepal since 2-3 decades now. Nearly a dozen of AIS is said to have started
showing the invasive characteristics in different ecosystems in Nepal. Due to the lack of
sufficient knowledge however, it remains to develop the knowledge base.
Emerging need: Alien species
are increasingly becoming serious threat to the environmental and economic well-being
locally and globally. There is a growing need to develop the knowledge base on alien
species, their behaviour in the ecosystems they have been introduced and their nature,
scale and intensity of propagation/colonisation. This type of study complemented with
similar information from the countries where they have already been introduced would be
useful to understand the interaction of such aliens with their ecosystems and help in
predicting the potential risk of invasion. Moreover, it is high time to understand the
aliens that have already become invasive in Nepal so that their management could be
studied and tested to ensure the conservation of biodiversity and protection of production
base. Improved education and dissemination of information to all sections of the
international community is critical to stopping the spread of alien species. Yet useful
information that could help reverse or at least halt the problems is not being shared
sufficiently.
These Guidelines, developed by the Species
Survival Commission’s Invasive Species Specialist Group aim to help governments and
management agencies around the world prevent the introduction of alien invasive species,
or control and eradicate species which threaten their native species, habitats and
ecosystems.
The invasive nature of a species means that,
given opportune conditions, it may spread unchecked across geographical or political
boundaries. To be effective, an initiative to identify, control, or eradicate an invasive
species requires a coordinated approach, where lessons learned and methodologies applied
are shared widely. IUCN is uniquely positioned to facilitate such an exchange of
knowledge.
(The author is associated with IUCN Nepal)
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