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?