Exotic Species: Overview and Impacts

Biology 10522 April 2002

Exotic species:

a species which now occurs outside of the range in which it is thought to have evolved

Synonyms (with subtle differences): nonindigenous,

introduced, alien, naturalized, feral, escaped

Introduction of Exotic Species

• Humans move species around globe:– 50,000 non-indigenous species in U.S. – New Zealand has a predominantly

alien flora and fauna– 1000 of California’s 8000 plant

species are introduced

Questions about exotic species

• How do they arrive at new locations?

• What are the effects of exotic species?

• What are characteristics of successful exotic species?

• What characteristics make a habitat susceptible to invasion?

How do exotic species arrive to new habitats?

Intentional introductionsAccidental introductions

Good Intentions Gone Bad

1. Escapees from cultivation– Species brought to a new region where they

are planted (non-agricultural)• Goal practical or aesthetic

– Species able to exist without help (protection, fertilizer, extra water)• Usually adapted to similar ecological conditions

– Species establishes self-reproducing population

– May be augmented by additional introductions or escapees

Purple Loosestrife

• Native to Europe• Brought as ornamental plant• Now widely established in eastern and

midwestern U.S.• Purple loosestrife information

Agricultural Species Do Not Usually Become Established As

Exotics

Usually not hardy enough to establish self-sustaining populations– Need additional nutrients, water over

what is available in environment– Are tasty to non-human herbivores

• Lots of nutrients• Few defenses

Intentional Introductions, continued.

Goal to establish self-sustaining population in new locale– Motivation: practical or aesthetic– “Acclimitzation Societies”– Reminders of home– Examples:

• European Starling in U.S. • Opossum in Southern California

European Starling, Sturnus vulgarus

“I’ll have a starling taught to speak nothing but “Mortimer”—Hotspur, Henry IV, part I

1890: Eugene Schieffelin imports 60 starlings and releases in Central Park

2000: 200 million starlings in U.S.

Spread of European Starling

Shaded areas = breeding range;

Dots indicate records of birds in preceeding winters

Viriginia opossum, Didelphis virginiana

Opossum introduced to Southern California in 1940’s

Woody Guthrie, Tom Joad

Accidental Introductions: Agricultural

Contaminants• Annual European grasses in

California• Russian thistle in western U.S.

Russian Thistle

Russian thistle: adapted to invade via effective

dispersal

Annual Grasses in California

Accidental Introductions:

Hitchhikers

• Black rat on islands around world• Zebra mussels in fresh waters of

eastern U.S.• Brown tree snake in South Pacific• Anopheles mosquitoes in Hawaii

Zebra Mussel

• Hitchhiked in ballast of ships• First recorded in Great Lakes in • Now common • Problems:

– Economic: clogs filters, covers smooth surfaces (boats, dams, locks)

– Ecological: ultra-efficient filtration, outcompetes other plankton-feeders

Fact sheet on Zebra Mussels

Effects of Exotic Species

• Second-most important threat to native species– (behind habitat destruction)

• Have contributed to the decline of 42% of U.S. endangered and threatened species

Effects: Biology

1. Species interactions– Competition: starling– Predation: brown tree snake, Nile perch– Disease: West Nile Virus

Starlings evict less aggressive, native birds from nest holes

Brown Tree Snake (Boiga irregularis)

• native to eastern Indonesia, Solomon Islands, New Guinea, and the northern and eastern coasts of Australia.

• caused ecological, economic, and human health problems on Guam since arrived shortly after World War II.

• an aggressive predator, has caused local extinctions of native bird, bat, and lizard species.

• Fact sheet on brown tree snake

West Nile Virus

• insect-borne virus • First reported in Western Hemisphere 1999• Birds natural hosts • transmitted from infected birds to humans and other animals through the bites of infected

mosquitoes.

• USFWS information sheet

Effect of Exotic Species on Higher Level Ecological

Processes

• Nile Perch in Lake Victoria

• Tamarisk in southwestern U.S.

• Sudden Oak Death Syndrome in California?

Nile perch in Lake Victoria

• Nile Perch introduced to Lake Victoria 1955

• Voracious predators, eliminated an entire trophic level of native cichlids (a planktivorous fish)

• Lake is now choked with algae• More information

American Museum of Natural History Exhibit on Lake Victoria

Upshot:

• Kenya, Tanzania and Uganda control 6, 49, and 45 percent of the lake surface,

• Gross economic product of the lake catchment ~US$3-4 billion annually

• estimated population of 25 million people

• incomes in the range of US$90-270 per capita/year

Effects: Biology• Water availability: saltcedar or tamarisk• Information on tamarisk

Effects: Economy

• Cost to U.S. per year: $123 billion!

• U.S. Dept. Agriculture– annual productivity loss due to

exotic species – 64 crops at $7.4 billion.

• Example: glossy-winged sharpshooter

Questions about exotic species

• What are characteristics of successful exotic species?

• What characteristics make a habitat susceptible to invasion?

• Can effects of aliens be predicted?• How do we prevent bio-

homogenization?

Why did aliens prosper in New Zealand?

• Of the total New Zealand flora of 2,500 species, 500 are introduced:– introduced species account for most

of the vegetation– why were these species so

successful?• most natural habitats had been disturbed• because of low diversity and simple

structure, island ecosystems are generally more easily invaded

What can be done about exotic species?

• Prevent arrival • Monitoring of sensitive habitats for new

arrivals• Development of effective control

techniques– Biological control– Integrated pest management– Selective chemical control including genetic

engineering