Attack of the Aliens

Kudzu

Purposely introduced to the United States from Japan in

late 1800s as an ornamental and cattle feed.

In mid 1900s US Government actively encouraged the

planting of Kudzu to fight soil erosion

Now naturalized into approx. 10,000-12,000 square miles

Costs USA >$500,000,000 in lost crop lands and control

In USA:

% of threatened or endangered species Wilcove et al 1998

In USA:

% of threatened or endangered species Wilcove et al 1998

Wilcove et al 1998

57% of threatened or endangered plant species are imperiled by alien species

According to one estimate 39% of all extinctions in the USA since 1600

are due entirely to invasive species

What is an invasive species?

• National Invasive Species Information Center Definition:

– 1. Non-native (alien) to an ecosystem

– 2. whose introduction causes or likely to cause economic or environmental harm or harm to human health

• Plants, animals, microbes, arthropods, insects, etc.

• aka: introduced species, exotic species, non-indigenous species, transplants

http://www.invasivespeciesinfo.gov/whatis.shtml

• Approximately 10,000 known

exotic species in U.S. – 5,000 plant species

– 20 mammal species

– 97 bird species

– 53 reptile & amphibian species

– 138 fish species

– 4,500 arthropod species (2,520 in Hawaii)

– 11 earthworm species

– 100 aquatic species

– 88 mollusk species

– Untold thousands of microbes!

Common Pigeon

Zebra Mussel

Grass Carp

Cabbage White Butterfly

Japanese honeysuckle

Lion fish

Giant African Land Snail

Despite the large numbers of invasive species,

invasion is actually an unlikely process.

Most species that arrive to a new system are not

successful.

It is difficult to determine the rates of success since most

unsuccessful invasions are invisible. But some estimates

are 10-40% of introductions are successful.

Despite the large numbers of invasive species,

invasion is actually an unlikely process.

Most species that arrive to a new system are not

successful.

It is difficult to determine the rates of success since most

unsuccessful invasions are invisible. But some estimates

are 10-40% of introductions are successful.

Not all exotic species are invasive: Think of all the

invasive species we see everyday that are not a

problem. (e.g., garden ornamentals)

To become invasive, a species must

pass through several “filters”:

1)Transport

2) Establishment and naturalization

3) Invasion

Transport

• Transport can be natural but in many cases is human induced.

• Humans can accidentally or deliberately move species.

• Most microbes and invertebrates are accidentally introduced (example: the zebra mussel in ballast water). Most vertebrates are deliberately transported (example: python) but a few of the worst cases have been accidentals (example: the brown tree snake). Many plants and many of the worst invasive plants are moved deliberately.

Transport

• The fact that many of the worst invaders come from deliberate transport has some obvious policy implications. Basically the first thing we need to do in order to reduce species invasions is to stop deliberately moving organisms to areas outside their natural ranges!

• But of course these movements are not done with the intention of invasions (except in the case of “assisted migration”!) but rather with a positive intent: – Agriculture

– Ornamentals

– Pets

– Game species

– Biological controls

Transport

• Accidental transportation of potentially

invasive species will increase with

increased globalization and increased

mobilization

http://globaia.org/en/anthropocene/

Global transport is increasing

An increasingly global market means

more accidental (and intentional)

transport of exotic species which will

lead to more invasive species

From immigrant to Invader • Most invasive species experience a long time lag between introduction and

invasion.

• Species are introduced and experience little population growth for decades after which time they experience a rapid, often exponential, growth.

• For example, the Brazilian pepper which is a major problem in the everglades was introduced in the 1800s but did not increase in population and become a serious problem until the 1960s.

• This lag creates problems for management since it is hard to distinguish between species that are going to remain innocuous or fail and those that will eventually become invaders and need to be removed (but also provides window when management is feasible).

Brazilian pepper –

one major

invasive species

in the everglades

Examples of lag times between introduction and invasion/outbreak for 17

invasive plant species in China

Lag Time

30 yrs

50 yrs

50 yrs

20 yrs

30 yrs

50 yrs

150 yrs

50 yrs

10 yrs

5 yrs

15 yrs

60 yrs

300+ yrs

40 yrs

50 yrs

10 yrs

20 yrs

From immigrant to Invader What factors determine the length of the time lag and the eventual

success of invasion?

1. The number and arrangement of infestations (many separate

infestations are usually more successful than one large infestation).

2. Natural selection causing adaptation of species to new habitat

3. Habitat alteration, there may be a changes in habitat that allows for the increase in population

4. Tipping point: population change may be slow until the species reaches critical mass and then it explodes

5. Humans can encourage species and foster their survival as small populations until they become established

6. Undetected growth (i.e., does time lag really just represent our failure to detect growth?)

Can we identify future invaders?

Can we identify future invaders?

• Clearly there is luck involved, but some species have repeatedly become successful invaders in many widespread locations at different times and thus there is reason to believe that these species have certain characteristics that increase probability of transport/establishment/invasion.

• If we can identify these characters we will be better equipped to predict which species may invade in the future and design management strategies aimed at these specific species

• For example: make import of these species illegal and search for species at border crossings

• Alternative is the “guilty until proven innocent” strategy in which all species are regarded as potential threats until we can identify characteristics that indicate they will not become invasives (contrast to current strategy of “innocent until proven guilty”)

Can we identify future invaders?

• Some Characteristics associated with successful invaders: 1. High reproductive rate, short generation time (r-selected)

2. Long-lived

3. High dispersal rates

4. Single parent reproduction

5. Asexual reproduction

6. High genetic variability (can adapt fast to new conditions)

7. High potential phenotypic plasticity

8. Broad native range (broad tolerances)

9. Habitat generalist

10. Broad diet

11. Human commensal (valuable, cute, tasty, etc)

12. Population size constrained by species interactions (top down regulation or strong competition) in native range

For most species we do not know enough about their life-histories

to predict if they will be potential invaders or not.

Can we identify future invaders?

• For most species we do not know enough about their life-histories to predict if they will be potential invaders or not.

• One promising tool is phylogeny.

• You may predict that close relatives of proven invader species may be also good invasive species.

• Also predict that invaders will be phylogenetically distinct from target community (empty niche hypothesis)

– One study found that introduced but non-invasive grasses were more closely related to the native California grasses than were the introduced and invasive grasses

Can we predict which communities

are susceptible to invaders?

• Some habitats/areas have been repeatedly invaded (e.g., Hawaii) and thus there may be certain features that make some habits more or less vulnerable to invasion.

– Vacant niches - e.g. islands • Conversely this means that many

invaders would not find the necessary commensals such as pollinators, dispersers, etc

– Escape from biotic constraints • The Australian bushtail invaded New

Zealand 150 yrs ago. In NZ, the bushtail has few competitors, no micro parasites, few macro parasites (14 vs. 76 in Australia). Population densities in NZ are 10x greater in NZ than in Australia.

Can we predict which communities

are susceptible to invaders?

Some habitats/areas have been repeatedly invaded (e.g., Hawaii) and thus there may be certain features that make some habits more or less vulnerable to invasion

1. Vacant niches - e.g. islands

2. Escape from biotic constraints

3. Community species richness - more diverse communities are more stable and less invasable

– Intact tropical forests have few invasive species but risk may be increasing as we introduce more shade tolerant tree species through plantations

4. Disturbance - fire, floods, grazing, drainage, pollution

5. Proximity to vector - seaport, roads, etc

6. Climatically matched to habitat of invader

7. Absence of similar species

8. Naive prey

9. Absence of predators

10. Already invaded – may encourage more invasions

Invasive Species Impacts

Ecosystem modification

Resource competition

Aggression and its analogs

Predation

Herbivory

Pathogens and parasites

Hybridization

Chain reactions

Invasional meltdown

Ecosystem modification

Melaleuca quinquenervia

Water hyacinth (Eichhornia crassipes) in

Lake Victoria in Africa Caulerpa toxifolia in Mediterranean

Asian chestnut blight (Cryphonectria

parasitica) eliminated American

chestnut (Castanea dentata), which

comprised at least 30% of the canopy

trees.

Resource competition

Gray squirrel (Sciurus carolinensis) is

better forager than red squirrel (Sciurus

vulgaris)

House gecko (Hemidactylus frenatus) from

Southeast Asia and parts of Africa has

invaded many Pacific islands, lowering

insect populations that serve as food for

native lizards

Aggression and its analogs

red imported fire ant (Solenopsis invicta) zebra mussel (Dreissena polymorpha

Garlic mustard (Alliaria petiolata) Spotted knapweed (Centaurea stoebe)

Ship rat (Rattus rattus), Norway rat (R. norvegicus), Pacific rat (R. exulans), small

Indian mongoose (Herpestes auropunctatus), and stoat (Mustela erminea)

introduced to islands. Rats have caused the extinction of at least 37 species and

subspecies of island birds throughout the world.

Predation

Nile Perch

Deliberately introduced to Lake Victoria in the 1950s in the hope that a fishery would be established to provide food and jobs to local communities. Drove extinct over 200 of the 300-500 species of small cichlids in lake Victoria

House cats eating birds (in Britain house cats eat 20 million birds annually), in NZ cats have driven extinct 6 species and 70 populations of native birds. On Australia cats have driven extinct 6 rodent-like marsupials

Burmese python in the everglades

Brown Tree snake

Guam

The snake that ate Guam

• Shortly after World War II (~1950) the Brown Treesnake was accidentally introduced from the South pacific into Guam, probably as a stowaway in ship cargo.

• Prior to the Brown Treesnake, Guam only had Ramphotyphlops braminus, a secretive wormlike blind snake that eats only termites and ants

• Guam was predator free and the fauna was defenseless. Caused the extinction or local extirpation of nine of the twelve native forest bird species on Guam and two of the eleven native lizard species

Dissected Brown tree snake with multiple birds in belly

Birds: Native

Common Name Scientific Name Status on Guam

Wedge-tailed shearwater Puffinus pacificus extirpated *

White-tailed tropicbird Phaethon lepturus rare

Yellow bittern Ixobrychus sinensis common in suitable habitats

Pacific reef-heron Egretta sacra uncommon

Mallard Anas platyrhynchos extirpated *

Micronesian megapode Megapodius laperouse extirpated *

Guam rail Rallus owstoni

extirpated (currently reintroduced in a wildlife

enclosure)

White-browed rail Poliolimnas cinereus extirpated *

Common moorhen Gallinula chloropus rare

Brown noody Anous stolidus rare

White tern Gygis alba rare

White-throated ground-dove Gallicolumba xanthonura extirpated

Mariana fruit-dove Ptilinopus roseicapilla extirpated

Island swiftlet Aerodramus vanikorensis rare

Micronesian kingfisher Halcyon cinnamomina extirpated

Mariana crow Corvus kubaryi rare

Nightingale reed-warbler Acrocephalus luscinia extirpated

Guam flycatcher Myiagra freycineti extirpated

Rufous fantail Rhipidura rufifrons extirpated

Micronesian starling Aplonis opaca rare

Cardinal honeyeater Myzomela cardinalis extirpated

Bridled white-eye Zosterops conspicillatus extirpated

Lizards: Native

Common Name Scientific Name Status on Guam

Snake-eyed skink Cryptoblepharus poecilopleurus extirpated (last recorded 1969)

Blue-tailed skink Emoia caeruleocauda common (in some forested areas)

Azure-tailed skink Emoia cyanura extirpated

Slevin's skink Emoia slevini extirpated (last recorded 1945)

Moth skink Lipinia noctua uncommon

Mutilating gecko Gehyra mutilata uncommon

Island gecko Gehyra oceanica rare (last recorded 1989)

Mourning gecko Lepidodactylus lugubris common

Rock gecko Nactus pelagicus rare

Micronesian gecko Perochirus ateles extirpated (last recorded 1978)

Mammals

Common Name Scientific Name Status on Guam

Pacific sheath-tailed bat Embollonura semicaudata extirpated (last recorded 1972)

Marianus fruit bat Pteropus mariannus rare

Little marianas fruit bat Pteropus tokudae extirpated (last recorded 1968)

Herbivory

Goats (Capra aegagrus hircus)

introduced to the island of St.

Helena in 1513 are believed to

have eliminated at least half of

100 endemic plant species

before botanists had a chance

to record them.

introduction of the South

American cactus moth

(Cactoblastis cactorum) to

Australia, where it brought a

massive invasion of prickly

pear cactus (Opuntia spp.)

under control.

vs. benefit of....

Pathogens and parasites

Rinderpest

attacked many native ungulates, with mortality in some species reaching 90%.

Hybridization

North American mallard

(Anas platyrhynchos)

New Zealand grey duck (A.

superciliosa superciliosa)

Hawaiian duck (A. wyvilliana),

Fig. 1. Average daily number of visits/tree to

flowers of Bruguiera gymnorrhizaby insects

(black), birds (light grey) and other visitors

(dark grey) during the observation periods on

Guam and Saipan.

Fig. 3. Average daily number of visits/tree to

flowers of Erythrina variegata var. orientalis by

insects (black), birds (light grey) and other

visitors (dark grey) during the observation

periods on Guam and Saipan.

Moretenson et al 2008

Predation of birds by exotic brown tree snakes on Guam causes loss of pollination

Chain Reactions Species A affecting species B, then species B

affecting species C, species C affecting species D,

and so forth...

Saipan Guam

Predation of birds by exotic brown tree snakes on Guam causes loss of seed dispersal

Fig. 5. Seedlings (<0.5 m) and saplings (0.5–1.5 m)

associated with 16 and 18 trees (>2.5 m) of Bruguiera

gymnorrhiza on Guam (black bars) and Saipan (white

bars), respectively.

Moretenson et al 2008

Predation of birds by exotic brown tree snakes on Guam causes loss of

pollination and seed dispersal and subsequent decline in tree reproduction

Invasional Meltdown

Two or more introduced species interact in such a way that the probability

of survival and/or the impact of at least one of them is enhanced

Figs (Ficus spp.) introduced to Florida had until ca. 20 years ago remained where

they were planted, the species unable to spread because the host-specific fig

wasps that pollinate the figs in their native ranges were absent, so the figs could

not produce seeds. Changed abruptly upon the arrival of the figwasps of three of

the fig species, which now produce seeds. One of them, F. microcarpa, has

become an invasive weed, its seeds dispersed by birds and ants.

Is it all bad? • Corn, wheat, rice, other food crops plus cattle, poultry, and other livestock

= 98% US food system

• Honeybees are introduced from Europe – vital pollinators for many US crops

• “Assisted Migration” – deliberate introduction of species into an area that is predicted to have suitable climate and environmental conditions in the future

– May save the target species from extinction, may have negative population, community/ecosystem, and economic effects

• Biological control – control of ‘pest’ using natural enemies

– Of 1049 deliberate introductions for bio-control of weeds 8 were damaging

– Successful biological controls have decreased use of chemical fertilizers

Prevention and Control

• Quarantine (an ounce of prevention is worth a pound of cure)

• Cost of excluding invaders is often trivial compared to the cost of extirpating them. However, it is difficult to identify potential invaders and thus difficult to target them.

• Some countries like USA and Australia use “innocent until proven guilty approach” - backwards! should be “guilty until proven innocent”

• Sometimes WTO nations are stopped from prohibiting invasions because it is considered a "unlawful or protectionist trade barriers” rather than a legitimate attempt to exclude pests

Eradication

• Eradication usually requires sustained efforts with lots of personpower and money

• Most times unsuccessful. – The campaign to eliminate fire ants in southeast USA was called by EO

Wilson “the Vietnam of entomology”. Cost >$26 billion and has lasted 20+ yrs. Ants reinvaded and in many cases reinvaded faster than the native species. Range of ants expanded 7X during campaign. Many native species were lost and traces of pesticide have been found in lots of nontarget species, including humans.

• Hunting - successful in eradicating goats from the Galapagos islands, public hunting is usually non-targeted and not intense enough (www.invasivore.org)

• Maintenance control - keep it at an acceptable level

• Biological control – Introduction of a natural enemy of the target species - a planned

invasion

– There are success stories in which the enemy now keeps the pest numbers under control apparently for perpetuity (pest numbers go up enemy number respond). Pest is not eliminated but is controlled.

– But also failures: the introduction of the new world predatory snail to control the African Giant Snail in Hawaii led to extinctions of native species as the predatory snail ate a wide variety of species and did not specialize on the pest

• Cane toads