This document discusses invasive alien species and their impacts. Some key points: - Invasive alien species are non-native species that invade ecosystems, outcompete native species, and alter community structures and ecosystem processes. They are the second largest threat to biodiversity. - Invasive species cause extinction and declines of native species and cost economies billions annually. Control measures have been implemented nationally and internationally. - The document then discusses the invasion process, hypotheses for invasion success, biological attributes that confer invasiveness, impacts on communities and economies, and control strategies. It provides details on the nature, status, and management of invasive species.

1. “INVASIVE ALIEN SPECIES & ITS IMPACT ON
COMMUNITY STRUCTURE & ECOSYSTEM
PROCESSES AND THEIR POSSIBLE CONTROL
MEASURES”
BY-
EKTA SINGH
Ph.D. (FORESTRY)

2. ABSTRACT
Invasive alien species are non-native or non-indigenous species that invade an ecosystem,
acclimatize for survival and nutrition, and ultimately manipulate the local environment creating
a negative pressure for native plants. Invasive Alien Species (IAS) is the second biggest threat to
biodiversity after habitat destruction and are a major cost to the economic well-being of the
planet. They cause enormous and often irreversible harm to biodiversity around the world by
displacing native and useful species and changing ecosystems processes and community
structure. They are responsible for the extinction or decline of many species and continue to
pose a huge threat to many more. They cost economies billions of dollars every year, in lost
production, control and mitigation efforts, loss of ecosystem services, and many other ways.
Therefore there are several control measures that have been prepared nationally and
internationally to conserve native species from the negative effect of invasive alien species.
Keywords- Invasive alien species, Extinction, Ecosystem process, Community structure

3. CONTENT
◎ Introduction
◎ Nature and Status of Invasive Alien Species
◎ Invasion process
◎ Hypothesis related to the success of the invasion
◎ Biological attribute conferring invasiveness
◎ Impact of invasive alien species
◎ Impact of invasion on community structure and ecosystem process
◎ Economic loss
◎ Prevention and mitigation of invasive species
◎ Control measures
◎ Management Strategy against invasive species
◎ International initiatives for the control of invasive species
◎ India’s effort for control of invasive species
◎ Conclusion
◎ Reference

4. INTRODUCTION
◎ Invasive Alien Species are non-native or exotic organisms that occur outside their natural adapted ranges
and dispersal potential. IUCN (2000) defines Alien Invasive Species as an alien species which becomes
established in natural or semi-natural ecosystems or habitat, an agent of change, and threatens native
biological diversity.
◎ According to the Convention for Biological Diversity, invasive alien species are the second largest cause
of biodiversity loss in the world and impose high costs to agriculture, forestry, and aquatic ecosystems.
◎ The invasive alien species contribute enormously to global change because they harm human health, pose
a threat to biological diversity, and cause enormous economic losses. It now operates on a global scale and
will undergo a rapid increase in this century due to interactions with other global changes such as
globalization of markets, explosive rises in global trade, travel, tourism, and exchange of goods (Hobbs.
2000).
◎ The cost of damage caused by invasive species is estimated at 1.5 trillion dollars Per annum environment
and economic damage, which is close to 5% of global GDP (GISP, Global Strategy, 2008 - 2010).

5. NATURE AND STATUS OF INVASIVE SPECIES
◎ Invasive species are alien species that sustain self-replacing populations over several life cycles, produce
reproductive offspring, often in very large numbers at considerable distances from the parent and/or site of
introduction, and have the potential to spread over long distances, possibly leading to adverse effects on invaded
habitat (Richardson et al. 2011)
◎ Khurro et al. (2011 ) have presented an inventory of the alien flora of India, to show that there are 1,599 invasive
species, belonging to 842 genera in 161 families, constituting 8.5% of the total Indian vascular flora.
◎ Biogeographically, more than one-third (35%) of the alien flora in
India has its native ranges in South America, followed by Asia (21%),
Africa (20%). Europe (11%), Australia (8%), North America (4%);
and cryptogenic ( 1%). When 869 species (cultivated 812 spp., casual
57 spp.) were excluded from the analysis, 31% (225 spp.) of the total
naturalized species (730 spp.) belonged to the invasive category
(Khuroo et al., 2011).

6. INVASION PROCESS
◎ The essential first step in invasion by an alien plant is its introduction to an area beyond its previous
geographical range. Introduction of non-native species may occur through (i) Accidental introduction, (ii)
import for a limited purpose and subsequent escape, or deliberate introduction on a large scale.
◎ Once introduced, the invader colonizes the new habitat, produces new self-perpetuating populations, and is
naturalized by getting incorporated into the resident flora. This is followed by spread to new locations. The
invader is likely to exist for some time as a single or small-localized population. At some point in time,
however, the invader will enter a period of rapid expansion both in terms of total population size, and the
number and size of individual infestations. Finally, an invader will reach a stage at which it will be a major
problem.
◎ The invasion is not necessarily a smooth process; major episodes of population expansion may be punctuated
by uneventful periods. The statistical rule, known as the 10th rule, holds that 1 in 10 of imported species
become introduced, 1 in 10 of those introduced become established, and 1 in 10 of those established become
Pests (Sharma et al., 2005).

7. The process of Invasion can be summarized
as:
i. For the invasion to take place, a taxon
overcomes various geographic and
climate barriers through intentional or
accidental transport.
ii. Establishment as a result of successful
reproduction overcoming all the
barriers.
iii. Survival and persistence overcoming
the biotic and local environmental
barriers.
iv.Expanding the size population so as to
spread to new regions overcoming the
dispersal and habitat barriers.
v. Adapting to biotic environment and
biota in the new area.
INVASIO0N PROCESS
INVASIVE SPECIES
GERMINATION
ESTABLISHMENT AND GERMINATION
RAMET
RAMET
GENET
GENET
Increase in population size and naturalization
Dispersal to other habitats for founding secondary population
FIGURE-1: Recruitment model for invasive plant species. The invasive species
has to overcome geographical, environmental, and reproductive barriers, face
competition from indigenous species, and then proceed to colonize new locations
(based on Sharma et al., 2005).
SEXUALLY
ASEXUALLY
SEED
SEED BANK PROPAGULE
BANK
PROPAGULE

8. HYPOTHESES RELATED TO SUCCESS OF INVASION
Several hypotheses have been proposed to explain the success of species as invaders but most of them explain the
success of only some invasives to some degree in some circumstances (Catford et al., 2009). Some of the hypotheses
are briefly described below-
1. Propagule Pressure(PP)- Large supply and high frequency of introduction of plant propagules increase the
chance of successful invasion due to high genetic diversity, a continual supply of propagules, and a higher
probability of reaching a favorable environment.
2. Global Competition (GC) Hypotheses- A large number of different non-native species is more successful than
a small number.
3. Empty Niche Hypotheses (ENH)- Due to a limited indigenous species pool, the recipients, community, and
ecosystem are unsaturated so invaders can use the spare resources and occupy the unused niche.
4. Novel Weapon Hypotheses(NWH)- In the exotic range, non-native species can have a competitive advantage
against native species because they possess a novel weapon, that is, a trait that is new to the resident community
of native species and, therefore, affects them negatively.

9. 5. Local Pathogen Hypothesis (LPH)- Invader accumulates generalist pathogens while
remaining less affected than the native plant species, thus enhancing plant invasiveness. E.g.
accumulation of local pathogens contributes to the invasive success of Ammophila arneria in
North America.
6. Faunal Interaction Hypothesis (FIH)- Many introduced plants rely on mutualism with local
biota in the new range. E.g. Animal-mediated pollination and seed dispersal.
7. Ideal Weed Hypothesis (IWH)- Life history, weed characteristics and traits of the invading
species facilitate invasion by enabling them to outcompete indigenous species.
8. Adaptation Hypothesis (ADP)- The invasion success of non-native species depends on the
adaptation to the conditions in the exotic range before and/ or after the introduction. Non-native
species that are related to native species are more successful in this adaptation.

10. BIOLOGICAL ATTRIBUTE CONFERRING INVASIVENESS
The success of invasion is affected by various biological attributes of the species and the characteristics of
the habitat that is being invaded. Some of the biological attributes associated with invasive plants are
summarized below( Sharma et al., 2005):
1. Fitness homeostasis- The ability of an individual or population to maintain relatively constant fitness
over a range of environments is fitness homeostasis.
2. Seed Size and Seed Weight- According to Rejmanek and Richardson, small seed weight (<50 mg),
short juvenile period (<10 yrs.), and short interval between large seed crops (1–4 yrs.) are associated
with invasiveness of woody species in disturbed landscapes.
3. Animal dispersal- Vertebrate dispersal is responsible for the success of many woody invaders in
disturbed as well as undisturbed habitats. For example, lantana is widely dispersed, predominantly by
birds, sheep, goats, cattle, foxes, monkeys, and jackals leading to its spread.

11. 4. Geographical range- One of the likely predictors of species invasiveness is the size of the native
geographical range. The propagules of the species, having widespread distribution have a high probability
of transport to other countries or continents.
5. Alternative mode of reproduction- Vegetative reproduction is responsible for increased habitat
compatibility and therefore, for successful invasion. A combination of sexual and vegetative reproduction
contributes to the invasive potential.
6. Allelopathy- Allelopathy is one of the several attributes of a plant permitting it to invade and establish
in a new ecosystem. L. camara is capable of interrupting the regeneration process of native species by
decreasing germination, reducing early growth rates and survival by allelopathy.
7. Competition with native species- Alien species belonging to Exotic genera (and therefore possessing
traits different from those of resident species) are more likely to be invasive than the alien species with
native congeners. For example, the alien Agropyron desertosum outcompete the natives A. spicatu due to
more efficient use of soil water in the Great. Basin in California.

12. ENTRY PATHWAY AND VECTOR
◎ The routes by which invasive alien species enter new habitats are known as pathways and the means
by which they travel to new destinations are known as vectors.
◎ Humans are chiefly responsible for the intercontinental movement of non-indigenous species and
continue to play important roles in the regional spread of these species after they become established.
◎ For example, shipping constitutes the pathway and the ship ballast water as a vector for the introduction
of many coastal and marine invasive alien species.
◎ Whereas many exotic species have been introduced to control other exotic species is also the reason of
the spread of invasive species. For example, in Australia red foxes were introduced to control
introduced rabbits; the rabbits thrived, but the foxes caused the decline of native marsupials.

13. IMPACT OF INVASIVE SPECIES
The impacts of alien invasive species are immense, insidious, and usually irreversible. They may be as
damaging to native species and ecosystems on a global scale as the loss and degradation of habitats.
• Grasslands and Savannas- Many non-native types of grass including Bromus spp., Eragrostis spp.
and Imperata cylindrica have widely invaded the grassland ecosystem in different regions.
• Forests- Within tropics and subtropics, tree plantations and agroforestry are important sources of
biological invasions. For example- Eucalyptus from Australia is widespread in Southeast Asia, India,
and various parts of Africa.
• Fresh water Ecosystem- Invasive species are invading large areas of freshwater system in both
temperate and tropical region affecting the diversity of native species and water quality. Alien water
weeds like water hyacinth and water lettuce are a global problem.

14. ◎ Ecosystem Level Effect- The ecological consequences of some invasive species as predators and
herbivores, pests and disease-causing organisms, competitors, and having ecosystem-level effects are
briefly described below:
1) Predator and Herbivores- The brown tree snake (Boiga irregularis) was introduced from Indonesia
to Guam, an island in the West Pacific Ocean. Due to this many native species of birds have become
extinct in the rainforests of Guam as the snake consumes them in large numbers (Savidge, 1987).
Another example is the introduction of the generalist species such as goat, rabbit, pigs etc., which
have been the most destructive herbivores of the islands.
2) Pests and Disease- Invasive insect can harm crop plants and reduce their productivity and act as
vectors of disease among livestock and in human population. For example, Apple snails are
threatening the rice plants and wetlands in Asia.
3) Competitors- The effects of exotics as competitors are the most conspicuous with plants and
sedentary animals. For example, Some invasive species such as Kudzu wine, Zebra mussel, purple
loose fire, and water hyacinth compete with other native species for space, water, nutrients and light.

15. IMPACT OF INVASION ON COMMUNITY STRUCTURE AND
ECOSYSTEM PROCESSES
◎ Invasive species may alter community structure through exploitation competition (indirect interactions such as
resource use), and interference competition (direct interactions such as allelopathy in plants; Callaway and
Ridenour 2004).
◎ Invasive impacts on other species interactions, including predation, herbivory, parasitism, and mutualisms, can
change the abundance of species with certain key traits that influence ecosystem processes (Chapin et al. 2000).
◎ Changes in species and community structure can affect ecosystem services both directly and indirectly. Direct
effects include-
i. The decline in abundance of economically valuable species.
ii. Aesthetic values are commonly lost with the arrival of “nuisance species” such as invasive vines or aquatic
floating plants.
iii. Invasives that disrupt mutualisms pose risks, particularly for pollination and natural pest control services.
iv. Decreased genetic diversity and species extinctions also lead to loss of option value.
◎ Indirect effects include a potential decrease in ecosystem resistance and resilience to change, due to the
hypothesized link between stability and changes in biodiversity (Hooper et al. 2005).

16. Figure 2- Mechanisms of ecosystem service alteration by invasive specie (based on Kröner,
Heidelberg; 2006)

17. Impact of Invasive Alien Species on Energy, Nutrient and Water Cycling-
◎ Impact on Energy- Energy flows can be altered by changes in trophic interactions, food webs, and keystone
species. For example, the herbivore Pomacea canaliculata (golden apple snail) has dramatically decreased
aquatic plant populations in wetlands in Southeast Asia. This in turn has led to the dominance of planktonic
algae, high nutrient levels, high phytoplankton biomass, and turbid waters, with implications for water
quality and purification (Carlsson et al. 2004).
◎ Impact on Nutrient Cycling- Nutrient cycling can also be altered by invasive plants that fix nitrogen, leach
chemicals that inhibit nitrogen fixation by other species, release compounds that alter nutrient availability or
retention, including nitrogen and phosphorus, and alter topsoil erosion or fire frequency (Dukes and
Mooney2004). Mycria and Acacia tend to increase available nitrogen in system they invade in Hawaii.
◎ Impact on Water Cycling- They alter hydrological cycles by changing evapotranspiration rates and timing,
runoff, and water table levels. Impacts are greatest when the invaders differ from natives in traits such as
transpiration rate, leaf area index, photosynthetic tissue biomass, rooting depth, and phenology (Levine et
al.2003). Changes to water cycles may affect both water supply and regulation. Example- Decrease in
community water use due to water loss by the invasion of Bromus tectorum in New Zealand.

18. ECONOMIC LOSSES
◎ The economic losses due to invasive species can amount to billions of dollars every
year as their management cost include not only the cost of preservation, control, and
mitigation but also indirect cost due to significant impacts on the goods and services
provided by the ecosystem. It is estimated that about 137 billion US dollars are lost
per annum from an array of invasive species (Pimentel et al., 2000). The estimates
indicate that damages from 79 alien species cost US$ 120 billion for the United
States weed alone cost AUS$ 3.9 billion per year in lower farm income and costs to
the central and local government on monitoring, control, management, and research
on weeds was at least AUS$116.4 million each year (Pyek and Richardson, 2010).

19. PREVENTION AND MITIGATION OF ALIEN
SPECIES INVASION
◎ Mitigation can include eradication (eliminating the IAS completely); containment (keeping
the IAS within regional barriers); or suppression (reducing population levels of the IAS to an
acceptable threshold).
◎ A strategically important focus for eradication is to identify points of vulnerability in major
invasive pathways such as the International port airport for monitoring and eradication
activities. It Aims for the long-term reduction in abundance or density of alien invasive
species
◎ The four major steps to deal with the problem of alien species, i.e.,
i. Prevention- Prohibition of particular commodities in accordance with international
regulations.
ii. Early detection- Early detection survey locates problem species that are in process of
invading an area.
iii. Early eradication- It involves the complete removal of alien invasive species.
iv. Control- It is done when eradication is not possible.

20. CONTROL METHODS
◎ Control of Exotic species is a very complex matter which involves policy decisions, economic
analysis, ecological analysis, and technological capabilities.
◎ Control method should be socially culturally ethically acceptable efficient nonpolluting and should not
adversely affect native flora and fauna human health and wellbeing domestic animal or crop. The
different types of control methods are defined below (based on the National Invasive Species
Information Center)-
i. Biological control- This is the intentional manipulation of natural enemies by humans for the
purpose of controlling pests reducing the population using prey targeting the invasive species.
Includes the use of animals, fungi, or diseases typically from the targeted species home range to
control invasive populations.
For example- Salvinia is an indigenous species in Southeast Brazil and is associated with Weevil
(Cryptobagous salvinia) was introduced in Australia in 1980. The weevil was provided an effective
control of Salvinia fern.

21. ◎ Chemical control- includes the use of pesticides, herbicides, fungicides, and insecticides. Chemicals
should be specific as possible, non-persistent, and non-accumulative in the food chain
◎ Cultural control- it includes manipulation of habits to increase mortality of invasives or reduce it's its
rate of damage (selection of pest-resistant crops, winter cover crops, changing planting dates). Also
includes measures aimed at changing human behavior to address the issue of spreading invasives using
opportunities to educate people about practices to increase awareness to prevent the spread of
invasives (signage, public awareness campaigns).
◎ Mechanical control- techniques include mowing, hoeing, tilling, girdling, chopping, and constructing
barriers using tools or machines.
◎ Physical (or manual) control- It includes activities such as hand-pulling, digging, flooding, mulching,
manual destruction or removal of nests, egg masses, or other life stages; generally includes the
destruction of invasive species by hand.
◎ Habitat management to control in various involve measures such as prescribed burning grazing and
other activities.
◎ Education and public participation has to a mainstay of any approach dealing with prevention
eradication and control of invasiveness.

22. MANAGEMENT STRATEGY AGAINST INVASIVE SPECIES
◎ The optimal management strategy against invasive species to involved with time since, introduction as a
management efficiency decreases and management cost increases with time, in the detection of prevention
(information, regulation, legislation and quarantine measures) to early detection (interception, monitoring,
surveillance, and removal) to management (eradication, contaminant, and control) (Simberloff et al. (2013)
◎ Guiding principle on invasive species adopted by CBD (2002) to reflect these findings- Prevention is a Priority
response early detection, rapid response, and possible eradication should follow when prevention fails.
◎ New Zealand and Australia have significantly reduced the number of invasions after public perception shifted and
the biosecurity policy was adopted.
◎ The future management of invasive species requires an adaptive management approach to their invasion (Bhagwat
et., 2012).

23. INTERNATIONAL INITIATIVES FOR CONTROL OF
INVASIVE SPECIES
1. Convention on Biological Diversity- The convention on biological diversity recognizes the
importance of invasive species as a global problem. The convention on biological diversity in article
8th calls on the government “to prevent the introduction of control or those alien species which
threatened ecosystem habitat for species”.
2. Global Invasive Species Programme- The Global invasive species program (GISP) has been formed
in 1997 for controlling alien species that threaten ecosystem habitat and species. The GISP is the
component of the Diversitas and is coordinated by SCOPE, IUCN, UNEP, and CABI. It is preparing a
new tool and approaches for the management, control, and mitigating the impact of invasive species
on a local, national and global level.
3. Invasive Species Specialist Group of IUCN- The invasive species specialist group(ISSG) is part of
the species survival commission (SSC) of IUCN. Its aim is to increase awareness about biological
invasion and suggest ways to prevent control or eradicate invasive species.

24. INDIA’S EFFORTS FOR CONTROL OF INVASIVE SPECIES
◎ The National Biodiversity Action Plan (2008)- The country emphasized the need for regulation of
introduction of invasive alien species and their management and it aimed to develop a unified national
system for regulation of all introductions including their quarantine check, assessment, and release,
improving the management of invasive alien species and restoring the adversely affected ecosystems.
◎ Plant Quarantine Order 2003- Under Destructive Insects and Pests Act, 1914 has been issued by the
Directorate of Plant Protection, Quarantine and Storage to prevent the introduction of alien insects,
fungal or other pest species.
◎ National Institute of Oceanography (NIO)- Ministry of Shipping has identified the NIO as a lead
Research and Development agency for helping address ballast water management issues including port
biological baseline survey, ballast water risk assessment, and identification of ballast water discharge
sites under 'Global Ballast Water Management Programme' and 'Government of India'.

25. CONCLUSION
Biological invasion is one of the important causes of habitat destruction and ecological
disturbance. IAS is not restricted to plants and mammals but comes from almost every major
taxon of organisms. Human activities have dramatically increased opportunities for species to
travel around the world and to become invasive. IAS is a global problem, affecting every
country in the world. The impacts of IAS on natural ecosystems are usually irreversible. It costs
economies billions of dollars every year in direct losses and the indirect losses to economies
may equal or exceed the direct losses. The rapid growth in trade, travel, and transport is causing
the number of introductions to increase. Human activities are changing natural ecosystems and
making them more susceptible to a great diversity of IAS. It is therefore there is need to increase
awareness about biological invasion and suggest ways to prevent control or eradicate invasive
species among local peoples.

26. REFERENCE
1. Gyan P. Sharma, J. S. Singh and A. S. Raghubanshi 2005, Plant invasions: Emerging trends and future
implications, Current science 88:726-734
2. Singh, J.S., Singh, S.P. and Gupta, S.R., 2014. Ecology Environmental Science and Conservation. S. Chand
Publishers, New Delhi.
3. Prabhat Kumar Rai & J.S. Singh, 2021, Plant invasion in protected areas, the Indian Himalayan region, and the
North East India: progress and prospects, Proceedings of the Indian National Science Academy 87(7)
DOI:10.1007/s43538-021-00013-w
4. Heather Charles and Jeffrey S. Dukes, 2007, Impacts of Invasive Species on Ecosystem Services, ecological
Studies Vol 193
5. A. Rajasekaran, Priyanka Salunkhe and Monika Singh, DOCUMENTATION AND STATUS OF INVASIVE
ALIEN PLANT SPECIES IN INDIA, A Handbook ICFRE
6. N. Roychoudhury, P. B. Meshram and Rajesh Kumar Mishra, 2019, CERTIFICATE COURSE ON FOREST
ENTOMOLOGY AND PEST CONTROL (pp.72-77) Publisher: TROPICAL FOREST RESEARCH INSTITUTE,
JABALPUR
7. Control Mechanisms- National Invasive Species Information Centre

27. THANK YOU