Impact of invasive species on the environment. Why they are called invasive species and how they lead to loss of native species and lead to loss of biodiversity.

1. Invasive Species
Prepared by: Dhiman Dutta

2. Invasive species
 "Invasive species"—they may not sound very threatening, but these invaders, large
and small, have devastating effects on wildlife.
 Invasive species are among the leading threats to native wildlife. Approximately 42
percent of threatened or endangered species are at risk due to invasive species.
 Human health and economies are also at risk from invasive species. The impacts of
invasive species on our natural ecosystems and economy cost billions of dollars each
year. Many of our commercial, agricultural, and recreational activities depend on
healthy native ecosystems.

3. What Makes a Species "Invasive"?
 An invasive species can be any kind of living organism—an amphibian (like the cane
toad), plant, insect, fish, fungus, bacteria, or even an organism’s seeds or eggs—that
is not native to an ecosystem and causes harm. They can harm the environment, the
economy, or even human health. Species that grow and reproduce quickly, and
spread aggressively, with potential to cause harm, are given the label “invasive.”
 An invasive species does not have to come from another country. For example, lake
trout are native to the Great Lakes, but are considered to be an invasive species in
Yellowstone Lake in Wyoming because they compete with native cutthroat trout for
habitat.

4. How Invasive Species Spread
 Invasive species are primarily spread by human activities, often unintentionally.
 People, and the goods we use, travel around the world very quickly, and they often carry uninvited species
with them.
 Ships can carry aquatic organisms in their ballast water, while smaller boats may carry them on their
propellers.
 Insects can get into wood, shipping palettes, and crates that are shipped around the world.
 Some ornamental plants can escape into the wild and become invasive.
 And some invasive species are intentionally or accidentally released as pets. For example, Burmese pythons
are becoming a big problem in the Everglades.
 In addition, higher average temperatures and changes in rain and snow patterns caused by climate change
will enable some invasive plant species—such as garlic mustard, kudzu, and purple loosestrife—to move into
new areas. Insect pest infestations will be more severe as pests such as mountain pine beetle are able to
take advantage of drought-weakened plants.

5. Threats to Native Wildlife-Direct threats
 Invasive species cause harm to wildlife in many ways. When a new and aggressive
species is introduced into an ecosystem, it may not have any natural predators or
controls. It can breed and spread quickly, taking over an area. Native wildlife may not
have evolved defenses against the invader, or they may not be able to compete with a
species that has no predators.
 The direct threats of invasive species include preying on native species, outcompeting
native species for food or other resources, causing or carrying disease, and preventing
native species from reproducing or killing a native species' young.

6. Threats to Native Wildlife-Indirect threats
 There are indirect threats of invasive species as well. Invasive species can change the
food web in an ecosystem by destroying or replacing native food sources. The invasive
species may provide little to no food value for wildlife. Invasive species can also alter the
abundance or diversity of species that are important habitat for native wildlife.
 Aggressive plant species like kudzu can quickly replace a diverse ecosystem with a
monoculture of just kudzu.
 Additionally, some invasive species are capable of changing the conditions in an
ecosystem, such as changing soil chemistry or the intensity of wildfires.

7. Ageratina adenophora(Mexican devil)
 Synonyms: Eupatorium adenophorum, E. glandulosum, E. pasadense.
 Common names: Mexican devil, eupatory, croftonweed, thoroughwort, sticky snakeroot, catweed,
hemp agrimony, sticky agrimony, sticky Eupatorium
 Ageratina adenophora (croftonweed, Eupatorium) is a perennial herb or small shrub (family
shrub (family Asteraceae) found along the coast of California and in the South Coast and Transverse
Ranges. It prefers disturbed areas, coastal canyons, riparian areas and scrub, and is especially
invasive in mild coastal areas. Originally introduced to California as an ornamental plant,
croftonweed escaped cultivation by producing abundant seed that is dispersed via wind, water, soil
movement, and by clinging to animals and people.
 This invasive plant is considered noxious in parts of Asia, Australia, New Zealand and Hawaii.

8. Ageratina adenophora(Mexican devil)

9. Mikania micrantha(bitter vine, climbing hemp
vine)
 Mikania micrantha is a perennial creeping climber known for its vigorous and
rampant growth. It grows best where fertility, organic matter, soil moisture and
humidity are all high.
 It damages or kills other plants by cutting out the light and smothering them.
 A native of Central and South America, M. micrantha was introduced to India after
the Second World War to camouflage airfields and is now a major weed.
 It is also one of the most widespread and problematic weeds in the Pacific region. Its
seeds are dispersed by wind and also on clothing or hair.

10. Mikania micrantha
 Once established, Mikania micrantha spreads at an alarming rate,
readily climbing and twining on any vertical support, including crops,
bushes, trees, walls and fences. Its shoots have been reported to
grow up to 27mm a day. Vegetative reproduction is also efficient and
vigorous. Although intolerant of heavy shade it readily colonises
gaps.
 M. micrantha damages or kills other plants by cutting out the light
and smothering them. In this respect it is especially damaging in
young plantations and nurseries. It also competes for water and
nutrients, but perhaps even more importantly, it is believed that the
plant releases substances that inhibit the growth of other plants.
 M. micrantha is one of the three worst weeds of tea in India and
Indonesia and of rubber in Sri Lanka and Malaysia.

11. Mikania micrantha

12. Cuscuta campestris (Field dodder)
 Field dodder is a parasitic plant native to North America.
 It lacks normal roots and leaves, but does bear flowers and fruits.
 It has been introduced to many other parts of the world due to the fact that its hosts
include a number of important crop plants.
 C. campestris has yellow to pale orange true stems, about 0.3 mm in diameter, which
generally do not twine and attach to the host, but produce tendrils of similar appearance
which form coils and haustoria - a specialised root-like sucker which penetrates another
plant (a host) and obtains water and nutrients from it
 Introduced in Euromediterranean region, Siberia, Russian Far East, Western Asia, Central
Asia, India, Bhutan. Bangladesh, Sri Lanka, China, Japan, Indochina, Malaysia, eastern
Africa, Madagascar, Australia. Parasitic on many plant hosts, especially vegetable crops.

13. Cuscuta campestris (Field dodder)

14. Lantana camara (Shrub verbena)
 Lantana camara, commonly called lantana or shrub verbena, is
native to Central and South America. It is an upright frost-tender
3-6’ tall.
 It has escaped gardens throughout the world and is considered to
weed in many frost-free/tropical areas where it can rapidly spread
thickets.
 Lantana is one of the world’s ten worst invasive species and a
Concern for Bhutan. It competes with native plants for space and
also alters the nutrient cycle in the soil.
 This invasion has resulted in the scarcity of native forage plants for
If eaten, the leaves can induce allergies on the muzzles of
extensive feeding on lantana has led to diarrhoea, liver failure,
animal’s death.

15. Lantana camara (Shrub verbena/Lantana)

16. Invasive carps
 Carp are a family of fish native to Europe and Asia. Common carp (Cyprinus carpio)
has been in Bhutan for many years. The common carp is considered a nuisance fish
or a pest fish.
 The newest invaders, bighead carp, black carp, grass carp, and silver carp that
originated from Asia are collectively known as invasive carp or Asian carp. These
invasive carp species are causing issues in the rivers and surrounding waters.
 Invasive carp are fast-growing and prolific feeders that out-compete native fish and
leave a trail of environmental destruction in their wake.

17. Bighead carp and silver carp

18. Black carp and grass carp