The document discusses the ecosystem impacts of invasive species, examining mechanisms such as competitive release, natural enemy release, and facilitation that contribute to their abundance. It highlights various invasive species, their ecological consequences, and challenges they pose to native biodiversity, including altered fire regimes and habitat displacement. Additionally, it suggests integrated strategies for combating invasives, emphasizing prevention, early detection, and ecosystem restoration.

1. Ecosystem impacts of invasive species
HON 305V
Dr. Andersen

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?