The document discusses invasive species and their impacts. It defines native, non-native, and invasive species. Many species have been introduced intentionally or accidentally through human activities like transportation. Invasive species can negatively impact ecosystems by outcompeting native species for resources, preying on native species, introducing diseases, altering habitats, and through hybridization. Their introduction has driven many plant and animal species extinct. Characteristics like rapid reproduction and lack of natural predators allow some introduced species to become invasive.

1. Species invasion
S. R. Maharjan
Assistant Professor
Tribhuvan University, Nepal
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2. • Native species are those that normally live and
thrive in a particular community.
• They occupy specific habitats and have
specific niches in their native environment.
They have natural predators that help to keep
their populations in check.
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3. What is a non-native species?
• A species living outside
its native distributional range, which has
arrived there by human activity, either
deliberate or accidental. Non-native species
are not necessarily invasive.
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4. • An invasive species is one that arrives (often
with human assistance) in a habitat it had not
previously occupied, then establishes a
population and spreads autonomously.
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5. • The great majority of such invasions are by species
introduced from elsewhere.
• For instance, for the Hawaiian islands, almost half the
plant species, 25% of insects, 40% of birds, and most
freshwater fishes are introduced.
• figures for Florida are 27% of plant species, 8% of
insects, 5% of birds, and 24% of freshwater fishes. Not
all introduced species become invasive.
• New Zealand had no native mammals, except for three
bat species but now has 30 introduced mammals.
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6. How are species introduced? Process
of Invasion
• Unintentional pathways
– On any type of human transport such as
airplanes,cars,ship ballasts
– Water ballasts
– New routes such as canals
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7. • Intentional pathways
– Species introduced intentionally for agriculture,
aquaculture, recreation and ornamental purpose.
• Eg, german carp
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8. Notable invasive species
European starling
house sparrowPhragmites
purple loosestrife
zebra mussel
sea lamprey
emerald ash borer

9. Invasive Species
Some introduced
deliberately:
•Ornamental plants
•game animals
•domestic animals
•Biological pests
Some accidental:
•ballasts of ships
•unprocessed wood
•fruit shipments
•by-pass natural
barriers
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10. European starling
Monk Parakeet
Birds
Mute swan
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11. •First successful introduction was 60 European
starlings released in Central Park, NY. in 1890,
European Starling
–competes with
bluebirds,
woodpeckers
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12. •The House Sparrow
was introduced into
Brooklyn, New York,
in 1851.
House Sparrow
•Competition from the House
Sparrow for cavity nests can
cause decline of some native
species. 12S.R. Maharjan

13. Insects
Africanized Bees
• In 1956, African Honey
Bees were imported into
Brazil
•In 1957, 26 African queens
escaped
•Reached US in 1990
•More aggressive than European Honey Bees, have
killed 1,000 people
•Impact honey and pollination industries 13S.R. Maharjan

14. Insects
• Crop pests
– boll weevil, corn
borer
• Culex mosquitos
– carry avian malaria
and pox
– driven 20 Hawaiian
bird species extinct
Adult boll weevil
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15. Insects
• Asian Long-horned
Beetle
– attacks and kills
many native trees
Found in Chicago in 1998
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16. • Gypsy moth
•Introduced in
1860s
•Originally
brought to the US
for silk production
•now defoliates
entire forests
Insects
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17. Brown Tree Snake
Reptiles and Amphibians
•Introduced to Guam via cargo
transported by U.S. military
ships during World War II
•On Guam wiped out 9
of 13 indigenous bird
species
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18. Plants
Kudzu
•kills other plants by smothering them under a solid
blanket of leaves
•Introduced into the U.S.
in 1876
•promoted as a forage crop and an ornamental plant
until 1953
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19. Plants
Garlic mustard
Buckthorn•garlic mustard
outcompetes native plants
by modifying light, moisture,
nutrients, soil and space.
•Not as good food
for herbivores as
many native species
•poses a severe threat to native plants and animals
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20. Negative effects
on native clams
Zebra mussels cover
them and prevent them
from feeding and
moving
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21. Characteristics of invasive species
• general diet and habitat requirements
high abundance
• small body size
• good competitors
• social / gregarious
• Have few natural predators, parasites or diseases
• Have high reproductive rates
• Are long-lived
• Are pioneer species
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22. Characteristics of invasive plant
• Self-compatible
• Flower early
• Produces abundant seed
• Disperse seed widely
• Grow rapidly
• Spread asexually
• Strong competitors
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23. Impacts of invasive
species
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24. Ecosystem modification
• the physical structure of the habitat can be changed.
Introduced plant species can modify an entire
ecosystem by overgrowing and shading out native
species.
– introduction of a few North American beavers (Castor
canadensis) in 1946 has have converted forests of
southern beech (Nothofagus spp.) to grassland
– In Florida , introduced Australian paperbark (Melaleuca
quinquenervia) trees converted
Grassand to forests
– In parts of Hawaii, Asian and American mangrove species
have replaced beach communities to mangroove forests
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25. • South American water hyacinth (Eichhornia crassipes) now
covers parts of Lake Victoria in Africa ,many lakes and rivers in
the southeastern United States and various waterbodies in
Asia and Australia.
• Vast quantities of rotting water hyacinth, and consequent
drops in dissolved oxygen, can also affect many aquatic animal
species.).
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26. • Introduced species can change entire
ecosystems by
– changing the fire regime
– by modifying water or nutrient regimes.
– in Israel, Australian eucalyptus trees were
deliberately introduced to drain swamps
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27. Resource competition
• In Great Britain, the introduced North American
grey squirrel forages for nuts more efficiently
than the native red squirrel leading to the decline
of the latter species
• The house gecko (Hemidactylus frenatus) from
Southeast Asia and parts of Africa has invaded
many Pacific islands, lowering insect populations
that serve as food for native lizards, whose
populations have declined in some areas
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28. Aggression and its analogs
• The red imported fire ant (Solenopsis invicta)
and The Argentine ant from southern South
America attacks other ant species and great
declines in populations of native ant species
(Tschinkel 2006).
• The zebra mussel spreading throughout much
of North America, threatens the very
existence of a number of native freshwater
bivalve species,
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29. • Some invasive plants inhibit other species, by
producing chemicals. For example, the African
crystalline ice plant sequesters salt, and when
leaves fall suppress other species in higher salt
concentrations
• Diffuse knapweed (Centaurea diffusa) from
Eurasia and spotted knapweed (C. stoebe) from
Europe are both major invaders of rangelands in
America as that they produce toxic root exudates
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30. • Root exudates of garlic mustard, which does
not have mycorrhizal associates, are toxic to
arbuscular mycorrhizal fungi found in North
American soils.
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31. Predation
.
• Introduced rats, for example, have caused the
extinction of at least 37 species and
subspecies of island birds throughout the
world.
– for eg. (Rattus rattus), Norway rat (R. norvegicus),
Pacific rat (R. exulans), small Indian mongoose
(Herpestes auropunctatus), and stoat (Mustela
erminea
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32. The brown tree snake(Boiga irregularis) introduced to Guam
from New Guinea in cargo after World War II, has caused the
extinction or local extirpation of nine of the twelve native
forest bird species on Guam and two of the eleven native
lizard species (Lockwood et al. 2007).
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33. Herbivory
• Introduced herbivores can devastate the flora
of areas lacking similar native species,
especially on islands.
• Plant-eating insects have been successful in
many biological control projects for terrestrial
and aquatic weeds.
• However, occasionally, biological control
introductions of herbivorous insects have
devastated non-target native species.
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34. • Goats (Capra aegagrus hircus) introduced to the
island of St. Helena in 1513 are believed to have
eliminated at least half of 100 endemic plant
species before botanists had a chance to record
them (Cronk 1989).
• European rabbits (Oryctolagus cuniculus)
introduced to islands worldwide have devastated
many plant populations, often by bark-stripping
and thus killing shrubs and seedling and sapling
trees
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35. • in the United States, the Russian wheat aphid
(Diuraphis noxia) caused US$600 million
damage in just three years (Office of
Technology Assessment1993).
• In forests of the eastern United States, the
European gypsy moth (Lymantria dispar)
caused a similar amount of damage in only
one year (Office of Technology Assessment
1993).
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36. Pathogens and parasites
• Many introduced plant pathogens have
modified entire ecosystems by virtually
eliminating dominant plants.
• Introduced plant parasites can greatly damage
agriculture. For example, parasitic witchweed
(Striga asiatica)
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37. Hybridization
• If introduced species are sufficiently closely
related to native species, they may be able to
mate and exchange genes with them –a sort
of genetic extinction.
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38. Thank you
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