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A SELECTION FROM THE GLOBALINVASIVE SPECIES DATABASE
I U C NThe World Conservation Union SPECIES SURVIVAL COMMISSION
Contribution to the Global Invasive Species Programme (GISP)
The Invasive Species SpecialistGroup (ISSG) is a New Zealand-based specialist group of the Spe-cies Survival Commission (SSC) ofthe World Conservation Union(IUCN). It is chaired by Dr MickClout (University of Auckland).
The goals of ISSG are to reducethreats to natural ecosystems andthe native species they contain - byincreasing awareness of alien in-vasions and of ways to prevent, con-trol or eradicate them.
ISSG Office: School of Envi-ronmental and Marine Sciences(SEMS)University of Auckland (TamakiCampus)Private Bag 92019Auckland, New ZealandPhone: #64 9 3737 599 x5210Fax: #64 9 3737 042E-mail: [email protected]
Text: Sarah Lowe, MichaelBrowne and Souyad Boudjelas.Design and layout: Maj De Poorter
Cover image: Brown tree snake(Boiga irregularis). Photo: GordonRodda
Biological InvasionWhat happens when a species is in-troduced into an ecosystem whereit doesn’t occur naturally? Are eco-systems flexible and able to copewith change, or can a new arrivalhave far-reaching repercussions anddo permanent damage? Will some-thing special be lost forever? Doesit matter?
In the distant past, the earth’s moun-tains and oceans represented formi-dable natural barriers to all but thehardiest of species. Ecosystemsevolved in relative isolation. Earlyhuman migration saw the first in-tentional introductions of alien spe-cies as our ancestors attempted tosatisfy physical and social needs,but the magnitude and frequency ofthose early introductions were mi-nor compared to those associatedwith today’s extensive global tradeand passenger movements.
History is rich with tales of the dis-astrous outcomes of some inten-tional introductions such as that ofthe Nile Perch, which resulted in theextinction of more than 200 otherfish species. We can avoid repeat-ing such mistakes by learning fromhistory. Yet surprisingly, potentiallydamaging introductions continue.The ongoing release of the mos-quito fish that feature in this bro-chure, is a good example. Anotheris the questionable behaviour ofsome participants in the interna-tional garden seed and pet trade.
Careless behaviour leads to unin-tentional introductions. So-called‘accidents’ now account for themajority of successful invasions.
The list of “100 of the World’sWorst Invasive Alien Species” inthis booklet illustrates the incred-ible variety of species that have theability, not just to travel in ingen-ious ways, but also to establish,thrive and dominate in new places.Today, alien invasion is second onlyto habitat loss as a cause of speciesendangerment and extinction.
The genes, species and ecosystemsthat make up the earth’s biologicaldiversity are important becausetheir loss and degradation dimin-ishes nature. Species other than ourown have a right to exist and to re-tain their place in the world. We donot know how to estimate whichspecies are essential to ecosystemfunctioning, which are redundant,and which will be the next to flour-ish as the world changes. When weintroduce a new species into an eco-system, the full impact is often notimmediately apparent. Invasion byspecies such as Miconia calvescenscan change entire habitats, makingthem unsuitable for the original na-tive community.
Safeguarding the earth’s diversityis the best way to maintain our lifesupport system. There is evidenceto suggest that the biosphere actsas a self-regulating whole and thatdiverse systems may be more resil-ient. Island ecosystems, which haveevolved in isolation often have rela-tively fewer plants, herbivores, car-nivores and decomposers to main-tain essential processes and aremore vulnerable to invasion. Onislands around the world speciesextinction is increasing at an un-
precedented rate. A number of theinvasive alien species featured inthis booklet are contributing tothese losses.
Useful initiatives, which contributeto better management practices anda reduced incidence of biologicalinvasion, are being taken by com-munities all over the world. Inva-sive alien species are now a majorfocus of international conservationconcern and the subject of coopera-tive international efforts, such as theGlobal Invasive Species Pro-gramme (GISP). As awarenessgrows, people and their communi-ties are able to make informedchoices that will have lasting effectson their descendants.
The list of “100 of the World’sWorst Invasive Alien Species” thatis presented here is designed to en-hance awareness of the fascinatingcomplexity, and also the terribleconsequences, of invasive alienspecies. Species were selected forthe list according to two criteria:their serious impact on biologicaldiversity and/or human activities,and their illustration of importantissues surrounding biological inva-sion. To ensure the inclusion of awide variety of examples, only onespecies from each genus was se-lected. There are many other inva-sive alien species, in addition tothose on this list of examples. Ab-sence from the list does not implythat a species poses a lesser threat.We hope that, by raising generalawareness, the risks of furtherharmful invasions will be reducedin future.
Crazy Ant (Anoplolepis gracilipes)
Brown Tree Snake (Boiga irregularis)
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Photo: Gordon Rodda
Crazy ants (so called because of theirfrenetic movements) have invaded na-tive ecosystems and caused environmen-tal damage from Hawai’i to the Sey-chelles and Zanzibar. On Christmas Is-land in the Indian Ocean, they haveformed multi-queen supercolonies in atleast eight areas of rainforest, foragingin all habitats, including the rainforestcanopy. They are also decimating the redland crab (Gecarcoidea natalis)populations. In 18 months the crazy antswere able to kill 3 million crabs. Theland crabs play an important role inChristmas Island’s forest ecosystem
helping in litter breakdown and influencing forest composition by eating leaves andseedlings of rainforest trees. Crazy ants also prey on, or interfere in, the reproduc-tion of a variety of arthropods, reptiles, birds and mammals on the forest floor andcanopy. Their ability to farm and protect sap-sucking scale insects, which damagethe forest canopy on Christmas Island, is one of their more surprising attributes.Although less than 5% of the rainforest on Christmas Island has been invaded sofar, scientists are concerned that endangered birds such as the Abbott’s booby (Sulaabbotti), which nests nowhere else in the world, could eventually be driven to ex-tinction through habitat alteration and direct attack by the ants.
A native of Australia, Indonesia, Papua New Guinea, and the Solomon Islands, thebrown tree snake is thought to have hitchhiked to Guam on military aircraft in thelate 1940s or early 1950s. The lack of natural predators and ample prey allowed thesnake population to explode. By the 1970s it was found island-wide and had done
extensive economic and ecological dam-age. It has caused major power outagesacross the island and sometimes bitespeople, but is most infamous for its nearcomplete extermination of Guam’s na-tive forest birds. The brown tree snakeis a serious threat to the biological di-versity of other tropical islands. It is ableto conceal itself in cargo on boats andaircraft and even in airplane wheel-wellsand has reached destinations as far afieldas Micronesia, Hawai’i, mainlandUnited States and Spain. Areas most atrisk are wet tropical locations that re-ceive large volumes of human and com-mercial traffic.
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Avian Malaria (Plasmodium relictum)
Caulerpa infestation
Avian malaria was introduced to Hawai’i in exotic birds kept by settlers, but itneeded a vector to spread. This was made possible following the introduction of thesouthern house mosquito (Culex quiquefasciatus) in the water barrels of a sailingship in 1826. Hawaii’s unique native birds succumbed quickly because, unlike non-native birds, they have noresistance to avian ma-laria. Unique birds suchas the colour-fulhoneycreepers, whichevolved into a diverse ar-ray of species and sub-species to fill differentniches, are threatened bythis disease and by habi-tat loss. Avian malaria,through its mosquito vec-tor has contributed to theextinction of at least 10native bird species inHawai’i and threatensmany more.
Caulerpa was introduced to the Medi-terranean around 1984, possibly as wastefrom the Monaco Aquarium. There isspeculation that the species released intothe Mediterranean was a hardier cloneof the original tropical seaweed. Itadapted well to colder waters and hasspread throughout the northern Mediter-ranean where it is a serious threat to thenative marine flora and fauna. New colo-nies are able to start from small segmentsof this plant and, being an opportunistichitchhiker, it is a threat to the whole ofthe Mediterranean. Wherever it has es-tablished itself, it has smothered habi-tats such as the beds of native sea grassthat serve as nurseries for many species.On 12th June 2000, divers in a lagoonnear San Diego in the United States dis-covered a patch of Caulerpa measuring20 metres by 10 metres. In this case too,it is thought that the infestation occurredafter somebody emptied a fish tank into a storm-water drain. Luckily this invasionwas discovered at an early stage and measures were taken to eradicate it.
Caulerpa Seaweed (Caulerpa taxifolia)
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Honeycreeper with malaria carrying mosquitos
Feral Pig (Sus scrofa)P
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Strawberry Guava (Psidium cattleianum)
Feral pigs are escaped or released do-mestic animals. Introduced to many partsof the world, they damage crops, stockand property and transmit many diseasessuch as Leptospirosis and foot andmouth disease. Rooting pigs dig up largeareas of native vegetation and spreadweeds, disrupting ecological processessuch as succession and species compo-sition. They are omnivorous and theirdiet can include juvenile land tortoises,sea turtles, sea birds and endemic rep-tiles. Management of this invasive spe-cies is complicated by the fact that com-plete eradication is often not acceptableto communities that value feral pigs forhunting and food.
The strawberry guava isnative to Brazil, but hasbeen naturalised inFlorida, Hawai’i, tropicalPolynesia, Norfolk Islandand Mauritius for its ed-ible fruit. It forms thick-ets and shades out nativevegetation in tropical for-ests and woodlands. It hashad a devastating effecton native habitats in Mau-ritius and is consideredthe worst plant pest inHawai’i, where it has in-vaded a variety of natural
areas. It benefits from feral pigs (Sus scrofa) which, by feeding on itsfruit, serve as a dispersal agent for its seeds. In turn, the guava pro-vides favourable conditions for feral pigs, facilitating further habitatdegradation.
Miconia (Miconia calvescens)
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Western Mosquitofish (Gambusia affinis)
Miconia on a mountainside in Tahiti
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A highly ornamental tree from South America, Miconiawas introduced to a botanical garden on the island ofTahiti in 1937. Its huge red and purple leaves made ithighly desirable for gardeners. It was spread into thewild by fruit-eating birds and today, more than half theisland is heavily invaded by this plant. It has a superfi-cial and tentacular rooting system that contributes tolandslides and has become the dominant canopy treeover large areas of Tahiti, shading out the entire forestunder-story. Scientists estimate that several of the is-land’s endemic species are threatened with extinctionas a result of habitat loss due to Miconia. It has beenintroduced to other Pacific islands, including Hawai’iwhere it was introduced as an ornamental in the 1960s.The plant has since been found in many locations onthe Hawai’ian islands. It is still sold as an ornamentalplant in the tropics.
The mosquito fish is asmall, harmless-lookingfish native to the freshwaters of the eastern andsouthern United States. Ithas become a pest inmany waterways aroundthe world following initialintroductions early lastcentury as a biologicalcontrol of mosquito. Ingeneral, it is considered tobe no more effective thannative predators of mos-quitoes. The highlypredatory mosquito fisheats the eggs of economi-cally desirable fish andpreys on and endangersrare indigenous fish andinvertebrate species. Mosquito fish are difficult to eliminate onceestablished, so the best way to reduce their effects is to control theirfurther spread. One of the main avenues of spread is continued, in-tentional release by mosquito-control agencies.
Mosquitofish; male and female pair
Rosy wolfsnail (Euglandina rosea)
Small Indian Mongoose (Herpestes javanicus(auropunctatus))
This voracious and opportunistic preda-tor is native to areas from Iran, throughIndia to Myanmar and the Malay Penin-sula. It was introduced to Mauritius andFiji and to the West Indies and Hawai’iin the late 1800s to control rats. Unfor-tunately, this early attempt at biologicalcontrol has had disastrous impacts. Is-land populations of native fauna, whichhad evolved without the threat of a fast-moving, mammalian predator, were nomatch for the mongoose. It has causedthe local extinction of several endemicbirds, reptiles and amphibians andthreatens others including the rare Japa-nese Amami rabbit (Pentalagusfurnessi). The small Indian mongoose isalso a vector of rabies.
Native to the southeastern United States, the predatory rosy wolf snailwas introduced to islands in the Pacific and Indian Oceans from the1950s onwards as a biological control agent for another alien spe-cies, the giant African snail (Achatina fulica). The giant African snailwas intended as a food source for humans but became an agriculturalpest. In French Polynesia, the fast moving rosy wolf snail rapidlyeliminated local endemic species. One group threatened by the rosy
wolf snail is the Partulatree snails, which evolvedseparately from eachother in isolated valleysand exhibit a variety ofunique characteristics.Many Partula tree snailshave been lost alreadyand today the survivorsexist in zoos and in theworld’s first wildlife re-serves for snails. This in-vasion by a biologicalcontrol agent has causeda significant loss ofbiodiversity.
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Nile Perch (Lates niloticus)
Water Hyacinth (Eichhorniacrassipes)
This South American native is one of theworst aquatic weeds in the world. Itsbeautiful, large purple and violet flow-ers make it a popular ornamental plantfor ponds. It is now found in more than50 countries on five continents. Water hya-cinth is a very fast growing plant, withpopulations known to double in as littleas 12 days. Infestations of this weedblock waterways, limiting boat traffic,swimming and fishing. Water hyacinthalso prevents sunlight and oxygen fromreaching the water column and sub-merged plants. Its shading and crowd-ing of native aquatic plants dramaticallyreduces biological diversity in aquaticecosystems.
The Nile perch was introduced to Lake Victoria, Africa in 1954 tocounteract the drastic drop in native fish stocks caused by over-fish-ing. It has contributed to the extinction of more than 200 endemicfish species through predation and competition for food. The flesh ofNile perch is oilier than that of the local fish, so more trees werefelled to fuel fires to dry the catch. The subsequent erosion and run-off contributed to increased nutrient levels, opening the lake up toinvasions by algae and water hyacinth (Eichhornia crassipes). Theseinvasions in turn led to oxygen depletion in the lake, which resultedin the death of more fish. Commercial exploitation of the Nile perchhas displaced local men andwomen from their traditionalfishing and processing work.The far-reaching impacts ofthis introduction have beendevastating for the environ-ment as well as for commu-nities that depend on the lake.
Water hyacinth on LakeVictoria
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Additional Resources:
Global Invasive Species Database (and Early Warning System): ISSG hasdeveloped a Global Invasive Species Database (and Early Warning System).Key features of this database include its accessibility (it is available on Internet)and ease of use. A simple habitat matching model is used to predict which otherglobal regions are potentially at risk of invasion. These developments are car-ried out as part of the Global Invasive Species Programme (GISP), coordinatedby the Scientific Committee on Problems of the Environment (SCOPE). IUCN,CABInternational and UNEP are partners in GISP. The 100 of the World’s WorstInvasive Alien Species list and database is an integrated subset of the GlobalInvasive Species Database.
Aliens is the bi-annual newsletter of the Invasive Species Specialist Group(ISSG), a specialist group of the Species Survival Commission (SSC) of theWorld Conservation Union (IUCN). Its role is to put researchers in contact witheach other and to publish information and news of alien invasive species andissues.
Aliens-l is a listserver dedicated to invasive species. It allows users to freelyseek and share information on alien invasive species and issues, and the threatsposed by them to the Earth’s biodiversity. To subscribe, look for instructions onthe ISSG website.
IUCN Guidelines: The IUCN Guidelines For The Prevention Of BiodiversityLoss Caused By Alien Invasive Species (As approved by 51st Meeting of Coun-cil, February 2000 ) can be obtained from the ISSG office, orhttp://iucn.org/themes/ssc/pubs/policy/invasivesEng.htm
Websites: Invasive Species Specialist Group: www.issg.orgGlobal Invasive Species Database: www.issg.org/databaseIUCN-The World Conservation Union: www.iucn.orgThe Global Invasive Species programme: http://jasper.Stanford.EDU/GISP/
This booklet is printed as special lift-out in Aliens 12. For additional copies orfor information about Aliens, contact: ISSG office, School of Environmentaland Marine Sciences (SEMS), University of Auckland (Tamaki Campus), Pri-vate Bag 92019, Auckland, New Zealand Phone: ++64 9 3737 599 x5210,Fax: ++64 9 3737 042, E-mail: [email protected]
