2. Why do invasives become so abundant?
● Competitive release: Kept in check by co-
adapted competitors in native habitat
● Release from natural enemies: Kept in check by
“the 3 P's” (predators, parasites, pathogens) in
native habitat
● Facilitation: Alter habitat to make it more
favorable for themselves
● Allelopathy: Poison your neighbors
● Fire regimes: Burn your neighbors' homes down
3. Competitive release vs. natural
enemy release
● Ecologists have been debating the relative
importance of competition vs. the 3 P's since
the 1950's
● Still an active topic of research
● Real answer seems to be “it depends”
4. Allelopathy
● Yellow starthistle
(Centaurea solstitialis)
native to Eastern Europe,
highly invasive
throughout the Western
U.S.
● Roots produce 8-
hydroxyquinoline, toxic to
plants that have not co-
evolved with C. solstitialis
5. Altered fire regimes
● Cheatgrass (Bromus tectorum), native to Eurasia, now
found throughout the Western U.S.
● Creates dense stands of dry grass (i.e., fuel) in the
hottest driest summer months
● Natural grassland fire frequency in non-invaded areas
about once every 60-100 years
● Heavily invaded areas burn every 3-5 years
● Native vegetation not adapted to this high fire frequency
● Neither are native wildlife
6. Effects on invaded habitats
● The worst invasive
plants can establish
near-monocultures
that displace native
vegetation, and
reduce habitat quality
for native wildlife
7. Back to the 3 P's
● Introduced predators
can devastate native
animal communities
● Feral cats
● Green tree snakes
● Many of the worst
offenders are fish
8. Integrated strategy for combating invasive species
● Prevent additional introductions through
effective quarantine and regulation
● Early detection and rapid response to new
outbreaks
● Control and management of established
problem species through multiple means
● Restoration and recovery of natural ecosystems
9. Giant African Snail
(Lissachatina fulica)
● Voracious herbivore, major
pest (and nuisance) in
vegetable and fruit crops, and
in gardens
● Feeds on a broad range of
host plants
● Has established throughout
Indo-Pacific, Caribbean, Brazil
● Found in the U.S. in Florida
and Hawaii
10. Cane Toad
(Rhinella marina)
● Deliberately
introduced into
Australia in 1935 to
control pest insects in
sugarcane
● Largest toad species
● Eats everything
● Toxic to anything that
tries to eat it
11. Feral pigs
(Sus scrofa)
● Originally native to Europe, Asia, and North
Africa
● Now found on all continents except Antarctica
● Major problem in many areas, including (but not
limited to) Australia, Hawaii, Texas
● Carry many diseases of livestock and humans
including
● Foot and mouth disease
● Brucellosis
● Leptospirosis
● Toxoplasmosis
● Rooting and wallowing behavior damages native
vegetation, may promote erosion
● Opportunistic omnivores (they eat everything)
● Impact water resources for wildlife
12. House sparrow
(Passer domesticus)
● Native to Eurasia and North Africa
● Now found throughout the U.S., and
in many other parts of the world
● Can out-compete native granivorous
(seed-eating) birds
● Known to evict many native birds
from nests
● Swallows (here on campus)
● Woodpeckers
● Bluebirds
● Wrens
● Purple Martins
13. Tree-of-heaven
(Ailanthus altissima)
● Native to Asia
● Fast-growing, prolific seed-
producer, aggressive root-
sprouting; can sprout from
fragments
● Allelopathic
● Thrives in poor soils, tolerates
pollution
● Can form dense stands and
crowd out native vegetation
● Roots can damage sidewalks
and building foundations
14. Giant Hogweed
(Heracleum mantegazzianum)
● Crowds out native species
● Dies back in winter, thus can
promote soil erosion
● Produces toxic sap that can cause
skin irritation and blindness
● Established in Oregon,
Washington, and Pennsylvania
● British progressive-rock band
Genesis (Phil Collins, Peter
Gabriel) recorded a song about
Giant Hogweed
15. Garlic mustard
(Alliaria petiolata)
● Native to Europe,
established in U.S. in
th
the 19 century
● Aggressively
competitive,
allelopathic
● Able to out-compete
native forest-floor
plants
16. Russian olive
(Eleagnus angustifolia)
● Native to southern Europe and western Asia
● Displaces native vegetation mainly but not
exclusively in riparian (streamside) habitats
● Can fix atmospheric nitrogen, shade tolerant
● Forms dense stands
● Provides poor habitat for native birds
17. Water hyacinth
(Eichhornia crassipes)
●
Native to tropical South America
●
Now found in North America, Asia, Australia, Africa, and New Zealand
●
In U.S. found throughout the southeast, and in California and Hawaii
●
Chokes waterways, leads to massive amounts of decaying vegetation and
reduced flow; reduce dissolved oxygen levels, often leading to fish kills
●
Shade out other aquatic plants, as well as phytoplankton
●
Biological control promising
●
Can be used to make a wicker-like material that can be made into baskets or
furniture
●
Used in World War II in Southeast Asia to fool Japanese pilots into thinking
that lakes were open fields safe for landing
18. ● Questions on the material?
● Questions on any of the examples?
● Remember competitive release, the 3 P's, and
facilitation. What are the implications of these three
mechanisms for control of invasive species?
● What kinds of adaptations might species have to cope
with really high fire frequencies?
● Invasive predators and herbivores can be especially
devastating on islands. Can you think of reasons why
this might be true?
● What are the implications of so many widespread
invasive species for our concept of “pristine nature”?
● Observations on invasive species you've encountered?