Ecosystem impacts of invasive species HON 305V Dr. Andersen
Jun 19, 2015
Ecosystem impacts of invasive species
HON 305VDr. Andersen
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
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”
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
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
Effects on invaded habitats
● The worst invasive plants can establish near-monocultures that displace native vegetation, and reduce habitat quality for native wildlife
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
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
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
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
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
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
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
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
Garlic mustard(Alliaria petiolata)
● Native to Europe, established in U.S. in the 19th century
● Aggressively competitive, allelopathic
● Able to out-compete native forest-floor plants
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
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
● 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?