Another Alien invasive species Jatropha is under promotion in India.
Has any research organisation tested its invasiveness in Indiatridax?
The reference literatures say NO. Then on what basis planners are
allowing it in our ecosystem. Why Indian sources (over 300 biodisel
crops) have been ignored??? To give benefit to Foreign firms? Why
toxic Jatropha is not under cultivation in UK ? Why Indian land is in
target?

Pankaj Oudhia


Alien Invasive Species:
An Example of Biological Pollution
Vaskar Thapa

Introduction
A number of non-indigenous species introduced intentionally or
unintentionally are found to cause serious ecological and economical
problems, because of their dominating and invasive nature over the
native species. Such species are known as alien invasive species. Not
all exotic species exhibit invasive behavior. Many of them are the
basis of modern agriculture, horticulture, forestry, foriculture and
aquaculture and no evidence of their negative impacts on the
environment have been reported. However, some exotic species tend to
behave differently in new environment. They propagate rapidly
infesting large area in short time and out compete native species
with irreversible effects. It is not known exactly what stimulates
them to be invasive but in number of instances it appears that the
biotic and a biotic components of new place along with the nature of
the species itself are important factors.
Some habitats are found to be more susceptible to invasion in
comparison to others. For example disturbed habitats with over-
utilized or over- grazed vegetation type provide suitable conditions
for colonizers. Eutrophic and polluted lakes and ponds are observed
easily attacked by floating waterweeds. Island habitats also appear
vulnerable to invasion, perhaps because of vacant niches or
uncompetetiveness of island species. Similarly, plants with prolific
vegetative or asexual or both reproductive mechanisms spread widely
and establish firmly in new habitats exhibiting high adaptability.
Animals capable of preying on a wide range of organisms and out-
competing, hybridizing with, and infecting native species also appear
to be aggressive colonizers.
It appears that faster travel, increasing global trade, habitat
loss, population growth, changing land use pattern due to deeper
penetration and exploitation of formerly remote areas are increasing
the likelihood of further introductions (Kins 1996, Hobbs and
Hamphires 1995). The problem is likely to grow in severity in the
coming decade with the changing global climate coupled with extensive
mobility of humans in all parts of the World (McNeely 1996).

Threats from Alien Invasive
The threats posed by alien species to the global biodiversity are
depressing, insidious and ever increasing. It is believed that
harmful invasions are second most serious threat to the global
biodiversity after habitat loss (Glowka et al 1994). Invasive species
often disrupt ecological processes by competing with, preying on,
hybridizing with or infecting native species. This often results in
the replacement of existing ecological strata and breaking down the
biological isolation of co-evolving species in long established
communities. Since biological isolation is an important component in
evolutionary process that maintain genetic diversity, the long term
impact of alien species may lead to “homogenization” (Soule 1990,
Clout 1995) - that is establishment of communities with species of
similar genetic characters or with less genetic variability. It may
cause native species endangerment and irreversible extensions. Hence,
alien species can be viewed as biological pollutants, but unlike
chemical pollutants, biological pollutants can adopt, reproduce and
spread, thus producing impacts that are virtually irreversible.

One can find number of examples in the natural ecosystems that have
evolved over millennia and now have changed beyond recognition due to
the spread of invasive species. For example Hawaii’s unique dry land
vegetation was completely out- competed and replaced by invasive fire
tolerant grasses. Similarly once diverse fish fauna of Lake Victoria
was preyed on and out-competed by the Nile perch and the rare trout
species of the American Southwest was hybridized and genetically
swamped by stocked rainbow and cut throat trout (McNeely et al 1996).
In case of Nepal comprehensive studies on the invasive species have
not been done so far. However, there are reports, which suggest the
seriousness of the problem. For example, Eupatorium adenophorum, a
shrub locally know as “Banmara”, has been colonizing the degraded
forests and agriculture lands extensively in the sub-tropical to
temperate regions of the country since the last forty years or so.
The species is believed to be native to South America and introduced
to Nepal from India. Similarly, Echornia sp. is found invading many
natural lakes and ponds of Nepal, especially in lowlands. Lantana
camera is another species that has been extensively encroaching
roadsides and forest edges suppressing native species. Its thorny
nature, adaptation potential to dry and wide range of soil types and
the unpalatable nature to many livestock help the species to spread
widely.

Management options
Prevention, eradication and biological control are three management
options generally applied today to control the invasive species.
Prevention is more favorable and far economical approach than solving
it after disruption. This is participatory approach for which
knowledge and resources available on invasive species should be
shared in most effective manner, thereby generating awareness on
invasive species. International cooperation is important in adopting
more stringent quarantine regulations and penalties as well as
improving transport hygiene standards. Promoting education and
awareness concerning the risks of biological invasions among
exporters, importers, travelers and general public are also essential
for preservation.
The option of eradicating alien species is a painstaking operation
suitable only where their removal is economically suitable. This
approach involves physical or chemical removal of the targeted
species and found to be successful only in small area. A principal
constraint of this method is the high and often recurrent cost of
labor. For example, the sea lamprey control program in the Greater
Lakes of North America cost about US dollar 10 million per year and
there is an ongoing need for the treatments (Alan Dextrase et al
1997). It appears in many instances that eradication is not a
complete solution but provides only short-term relief from the impact
of invasive species.
Biological management more than eradication is a control method. This
method involves the introduction of predators or pathogens of the
alien species (normally from its native range) to keep its number in
check. One hypothesis is that the major factor responsible for
species becoming invasive in new habitats is release from their own
specialized natural enemy that nature generally provides. Thus in the
approach, the natural enemy specific to the invasive species is
identified and utilized to regulate their population in a way that is
very similar to the natural system. Besides, predators and pathogens,
techniques such as release of sterile males and velocity barriers on
spawning streams are currently being applied in the sea lamprey
program in the Great Lakes as alternative control measures.
The first dramatic success in controlling alien cactus plant (Opuntia
sp) through biological means was achieved in Australia. By the early
part of the twentieth century, these cacti had invaded millions of
hectares of natural grassland and forest of Australia. In 1926, a
moth native to South America, Cactoblastic cactorum was introduced in
Australia as a natural enemy to the weed species and within a decade
of introduction, the population of solid stands of the weed had
collapsed over an area of about 25 millions hectares in the eastern
Australia. The control was permanent - the balance between the weed
and its natural enemy was maintained, with insects quickly
suppressing the occasional local resurgence for the weed. Similarly
success was also achieved in resurrecting a principal native tree
called tree daisy or green wood (Commidendrum robustrum) in St.
Helena of the South Atlantic. Sometimes in early 1990, this remnant
population becomes infested by an alien scale insect, Orthezia
insignis that damaged the gum wood on a large scale. A biological
control program initiated to solve the problem identified a
specialized natural enemy, the ladybird (Hyperaspis pantherina)
native to South America where scale insect was found naturally. The
predator was released in 1993 and recent evaluation of the program
has proved to be successful in controlling 80% of the damaged caused
by the insect. The scale insect population has declined drastically,
death of the tree has stopped and the trees are regenerating.
Most management programs for alien species affecting conservation
have a biological component, because this is one of the few options
for permanent control, which is affordable and environmentally sound.
The cost-benefit ratio of such program shows that it is highly cost
effective can be typically in ration of 1: 10 to 1: 100 (Jeff Waage
1997).

Conclusion
Management of alien species is crucial for the conservation of
biodiversity. The impacts of alien species at various scales exist
almost all over the World. It seems that the environmental
destruction caused by humans in various ways is providing more
opportunity for alien species to spread. Its impact if not tackled in
time would be serious threat to the World’s biodiversity.
Initiatives taken by the International conservation organizations
such as IUCN-The World Conservation Union, International Institute of
Biological Control, Canadian Wildlife Service and World Wide Fund are
certainly noteworthy on a global scale however to make them effectual
their efforts should be reached to grass root levels. Otherwise as
described by Marsden (1993), “introductions, like extinction, are
forever” and the environmental burden resulting from them will be
passed on to our future generation, when it may be too late.

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