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