1

Invasive Alien Species Problems in Japan:
an Introductory Ecological Essay
Izumi WASHITANI
Institute of Agricultural and Life Sciences, The University of Tokyo
Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan

Abstract
Status of invasive alien species problems in Japan is briefly summarized, with special emphasis on
invasions during the period from the 1960s to today, one of the two eras characterizing the modern history of the biological invasion into Japan. A number of cases of invasions are categorized from theviewpoints of route of invasion, i.e., intentional or unintentional introduction, release and escape; andtypes of impacts of invasive alien species on ecosystems, biodiversity, and human life and health.
Examples are given of species and situations exemplifying the individual types of influences.
Key words: impacts on ecosystems and biodiversity, intentional or unintentional introduction,
invasive alien species, modern biological invasion

1. Scope of the Introductory Thesis
Aside from the urgent social need for investigationof invasive alien species problems, Japan is an interesting country to investigate regarding biological invasion, since it is an island country with clear oceanic
boundaries, having a somewhat unique biota.
The Japanese Archipelago was a part of the AsianContinent until 15 million years ago when the Sea ofJapan was a young marginal basin located between
Japan and the Asian Continent (Chinzei, 1991). Before
that geological age, the Japanese islands were notseparated from the Eurasian continent, but formed theeast end of the continent. Even after their separationfrom the continent, intermittent formation of landbridges during the Ace Ages (Nogami et al., 1980)
facilitated active migration and colonization events ofplants and animals including mammoths and humans
from the continent to the islands. Therefore, Japaneseflora and fauna are fairly similar to those of continental East Asia, but the endemism is moderately highdue to the relatively long history of land isolation.
After the long period of national seclusion during
the Edo Period corresponding to the period of European colonization, the country was reopened and waseager to incorporate not only western cultures andtechniques, but also biotic matters. After more than
one hundred years of striving, contemporary Japanesesociety, like an “Asian and Western” cultural chimera,has been formed with its flora and fauna well blended
with plants and animals of European and North
American origins (Totman, 2000). At present, Japan isclearly losing the battle against biological invaders,Global Environmental Research8(1)/2004: 1-11
printed in Japanand now stands at a critical moment.
In this introductory essay heading this special issue,
I attempt to present a brief sketch of the present statusof the problem of invasive alien species in Japan,
focusing on ecological as well as social mechanisms
of invasions, and their impacts on biodiversity, ecosystems, and human activities and health.

2. Phases of Modern Biological Invasion
Biological invasion depends on chances for orroutes of invasion on the one hand, and the presenceor abundance of habitats where the introduced species
can establish themselves on the other. Active foreign
trade inevitably facilitates both intentional and unintentional introductions. On the other hand, humanreformation of habitat conditions through development of roads, farmlands, plantations and cities prepares new habitats with ample void niches no native
species have preempted.
Two eras can be distinguished in the modern history of biological invasion into Japan. One is the Meiji
Era when Japan’s modern foreign trade officially began after the long national seclusion under the
Tokugawa shogunate (Asao, 1998). This era simultaneously marked a new departure into industrialization.
The recorded years of the first naturalization of many
contemporarily common non-native plant species
were in the Meiji Era (Washitani, 2002). Since thattime, the numbers of both naturalized alien vascularplant (Fig. 1) and insect (Kiritani, 2002) species havebeen constantly increasing. Therefore, ‘alien species’in Japan are generally defined as the modern alien©2004 AIRIES

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species that were introduced after the start of the Meiji
Era (Murakami & Washitani, 2002).
Another era demarcating the different phases ofalien species invasions into Japan was the rapid economic growth period starting in the 1960s when Japanese landscapes began to change greatly due to various types of development works according to a national plan to “remodel the Japanese archipelago”(Tanaka, 1972). After that era began, invasions havebecome more frequent than ever (Kiritani, 2002;
Washitani, 2002). The globalization of trade and enhanced human habitat alterations can be considered
the major reasons for accelerated invasions.
Certain currently devastating alien species are
known to have begun abrupt population growth andrange expansion after various lengths of lag periods
after their initial invasion, and this suggests some important ecological and/or evolutionary changes oradaptations, such as establishment of a new mutualism
in pine wilt disease (Kiritani & Morimoto, 2004), alterations of seasonal life cycles in the fall webworm,
Hyphantria cunea (Gomi, 1995), and acquisition ofpesticide resistance in Erigeron philadephicus L. var.
philadephicus (Ito & Miyahara, 1984).

3. Route of Invasion: Intentional Introduction
Quantitative aspects of introduction are among themost important factors governing the probability ofinvasion of an alien species, since the invasion generally depends on various stochastic processes. Therefore, chances of invasion are optimal if the plants oranimals are intentionally introduced in large quantities
continuously into a region with ample void niches.
This holds with alien grasses and legumes, which havebeen massively introduced for erosion prevention or
revegetation purposes at various construction worksites (Washitani, 2001).

Number of species

1600

1200

800

400

0
1860

1880

1900

1920

1940

1960

1980

2000

2020

year
Fig. 1 Changes in the number of the naturalized plant
species (drawn according to data from Washitani& Morimoto, 1993, and Ecological Society ofJapan, 2002).

Erosion prevention techniques using alien perennial grasses, which cost much less than traditional
techniques using Zoysia japonica, were first developed as afforestation and landslide prevention techniques and then also applied to construction of highways, roads and dams, and to other developmental
works (Washitani, 2002). Vast quantities of seeds havebeen imported mainly from North America, mixed
with organic malting materials and chemical fertilizer,
and mechanically plastered to the denuded ground or
slopes to be revegetated.
During the age of mass construction works inJapan, that is, the 1960s-1980s, alien grasses, cultivarsof Eragrostis curvula of South African origin (seedsof which were introduced from the USA), Lolium
multiflorum L. and Festuca arundinacea were popularplant materials for revegetation. These species areamong the most invasive plant species in riparian
habitats and up to 1999, the total area of vegetation
dominated by alien grasses reached 18,000 ha, whichamounted to 12% of the total river area administeredby the Ministry of Land, Infrastructure and Transport(Miyawaki & Washitani, 2004).
Legume trees and shrubs were also common as
revegetation plant materials. Aggressive invasions ofthese grasses and legumes currently contribute a profound threat to the biodiversity and ecosystem integrity of Japanese riparian habitats (Washitani, 2001;
Muranaka & Washitani, 2002).
Stocking rivers and lakes with alien fishes has
been also a major route of biological invasions into
fresh aquatic ecosystems. Representative is the stocking of rainbow trout and brook trout imported fromthe USA, that began as early as 1877 (Kawanabe,1980), and their populations have become establishedin regions with cooler climates in Hokkaido andHonshu. Currently, brook trout are suspected tothreaten native white-spotted charr through competition and asymmetric hybridization (Kitano, 2004).
The most notorious invaders attracting contemporary public concern are some sunfish family species
native to North America, which have been repeatedly
released into lakes and ponds for sport fishing andhave explosively multiplied (Yodo, 2002). Largemouth bass, which are known to prey on a wide rangeof native species including fishes and insects such as
dragonfly larva (Suda, 2002), were reported in only 23
prefectures of Japan in the early 1970s, but are now
distributed in all 49 prefectures (A round - tableconference on alien fish problems, 2003 ).
Collapse of fishery grounds due to predation byillegally stocked bass and bluegill has been reported
from 305 fishery grounds subjected to fishery rights,
including 257 rivers and 48 lakes, in all parts of Japan(source: interview with the National Alliance of Inland
Fishery Association). Bylaws to ban the release of
several alien fishes including bluegill and large-mouthbass were enacted in the late 1990s by most selfgoverning bodies at the prefecture level.

Invasive Alien Species Problems in Japan: an Introductory Ecological Essay

Biological hazards due to the naturalization of intentionally introduced agricultural biotic agents are
not yet fully recognized, but it should be noted that
unlike non-living materials, biotic agents may propagate, adapt to new environments through evolutionarychanges and expand their ranges actively. It is possiblethat a minute quantity of an introduced biotic agent
could have a great impact on an ecosystem after its
population or range increased a million or billion fold.
A symbolic case of immediate naturalization after
introduction for agricultural use is found in Bombus
terestris, which has been introduced as a pollinator forgreenhouse cultivated tomatoes since 1991. Japanese
greenhouses are not closed systems in their structure,and the introduced bees can escape freely. A naturalcolony of the species evidencing naturalization was
found in Hokkaido as early as in 1996 (Washitani,1998), and the results of a voluntary monitoring activity suggest rapid population growth of the species inthat region (Matsumura et al., 2004).

4. Route of Invasion: Unintentional Introduction
One of the most influential alien species that was
unintentionally introduced in the early phase of thehistory of the modern biological invasion into Japan isa pathogenic nematode (Bursaphelenchus xylophilus).
The species is thought to have made its invasion byhiding in imported wood for shipbuilding from North
America, and has caused tremendous damage to pine
plantations throughout Honshu, Shikoku, and Kyusyu
since its first record in Nagasaki in 1905 (Togashi,
2002).
Postwar Japanese foreign trade has been characterized by imports of raw materials and exports of industrial products such as automobiles (Kodansha International, 1999). Origins of various invasions into Japan
can be ascribed to the intermingling of biotic andother materials imported.
In particular, mass import of cereal is likely to be
most responsible for the dissimilation of weevils andarable weeds from exporting to importing countries.
In Japan, only eight insect species were recorded as
stored product pests in the Meiji Era, but at present as
many as 108 can be listed (Nakakita, 2002). A numberof notorious weed invasions into Japan demonstrated
that unintentional introduction is inevitable for crop
field weeds with seeds ecologically mimicking crop
grains. The predominant major cereal exporting country to Japan is the USA, whose share accounted for
92.5% of corn and 78.7% of soybeans on average
from 1996-1998 among the countries that export cereal to Japan (Ministry of Agriculture, Forestry and
Fisheries, 2001).
Soybeans were the most important protein sourcein the traditional food habits of Japan, but the domestic supply of soy is very low and more than four million tons of soybeans are transported yearly from the3

United States. Japanese soybean food manufactures
have to discard large amounts of weed seeds intermingling with imported soybeans. Therefore, the weeds
can spread from the dumping grounds of such factories. Representative is Ambrosia trifida, native to estuarine floodplains of North America (Sickels &Simpson, 1985), but is now very common in Japaneseriparian habitats and landfill sites where industrial
wastes are dumped (Washitani & Morimoto, 1993).
The current Japanese livestock industry strongly
depends on imported cereal for feed. Serious contamination by weed seeds of imported cereal was reported
by Shimizu (1998) who inspected feed cereal cargos
landed from ships at Nakaminato Port in Ibaraki Prefecture in the Kanto district. During one year of investigation, the seeds of more than 100 alien weed
species were detected. The seeds of 64 weed species
were found in soybean cargos imported from the USA.
In another investigation of cereal cargos of 105 ships
from various regions of the world, the seeds of a totalof 1,482 weed species were detected intermingling
with cereal (Shimizu, 2002).
Another route of mass introductions associatedwith foreign trade is via ballast water of ships carrying
a large number of living marine organisms. Ballast
water is known as a major source of many notorious
invasions worldwide in the last quarter of the 20th century (Carlton, 1985, 2001). In Japan, many alienmarine species have become established in the coastal
areas of Tokyo Bay and Osaka Bay (Furota, 2002;
Iwasaki, 2002), which are surrounded by the mostdensely populated industrial cities of Japan. Heavily
polluted water drove away native species that wereabundant in the past, and the void niches thus formed
were suitable to certain alien species more resistant topolluted and deoxygenated conditions resulting fromexcessive nutrients (Furota, 2002). One representativeis the introduced spider crab (Pyromaia tubeuculata)
native to the Pacific coast of North to South America,
which was first recorded in Tokyo Bay in the 1960s,
and is now the most abundant crab in the bay (Furota,
2002). The shore protection walls of the bay aredensely covered with adhesive shellfishes broughtfrom various regions of the world, including Mediterranean blue mussel (Mytilus galloprovincialis),
Oceanic Xenostrobus secure, and Limnoperna
forutunei kikuchi, Southeast Asian Perna viridis,
North Atlantic Balanus eburneus and Molgulamanhattensis, on which Mediterranean green crabs(Carcinus aestuarii) wander. Off the coast, Pyromaia
tubeuculata are abundant on the seabed especiallyduring cool seasons when the bottom water layer isaerobic enough (Furota, 1996, 2002). In a survey
performed in 2000, 80% of the total individuals and
88% of the total fresh weight of sedimentary organisms were occupied by alien species (Environmental Bureau Tokyo Metropolis, 2002). These aresome of the results of invasions via ballast water.

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5. Pets Naturalized by Intentional Release orEscape6. Impacts of Invasive Alien Species on
Ecosystems and Biodiversity

Recently, pastimes or recreational uses of introduced plants and animals – such as for gardening,fishing and raising or breeding as pets – have caused
serious biological invasion problems. Japan is one of
the world’s biggest animal and plant-consuming countries (WWF- Japan, 1999). Today, every conceivablekind of pet animal, especially reptiles, amphibians,
and fishes including poisonous or hazardous ones, aswell as exotic insects are massively introduced (Cabinet Office, 2001b). In 2001, 782 million items of animals were imported (Seino, 2002). If just a small proportion of the imported organisms become naturalized,
the numbers could become considerably larger, andcertain naturalized organisms could have a great impact on ecosystems and society.
Escapes from zoos are one of the major routes for
mammal naturalization, as seen in a representative
case of the Formasan squirrel (Callosciurus erythraeus
thaiwanensis), which originated in Taiwan and is rapidly expanding in its range in Kanagawa Prefecture(Miyamoto et al., 2004).
A notorious example of naturalization due to abandonment or intentional release can be seen in the caseof Trachemys scripta elegans that has currently become the most common turtle in standing water habitats in Japan (NACS-J, 2004), because young individuals are among the most popular pets for children
and are usually abandoned when they grow to ferocious-looking adults (Yasukawa, 2002).
An embargo on the introduction of tropical beetles
based on the Plant Quarantine Law was partially canceled in 1997. During the first half of 2001, about
630,000 beetles were imported (Araya, 2002). A large
market for the imported beetles has been established,and various species and races are now imported fromvarious Asian countries (Traffic Japan, 2002). According to an investigation of a pet shop (Traffic Japan,
2002), they sell beetles labeled as native to countries
such as India, Nepal, Bhutan and the Philippines thatlegally ban the export of those species. Abnormalbooms of stag beetle breeding and consequent intentional and unintentional releases are suspected to be
responsible for the recent increase in size of Dorcus
antaeus caught from its natural habitats of Japan(Goka, 2004). Such an abrupt size increase cannot be
explained unless strong artificial selection and/or
crossing with individuals with a different genetic
make-up are assumed (Goka, 2004).
The list of naturalized pet animals in Japan includes raccoons, prairie dogs, green iguanas, common
snapping turtles and so on (Ecological Society ofJapan, 2002). Introduced turtles (Yasukawa, 2002) andraccoons (Ikeda, 2002) are likely to deprive native
turtles and raccoon dogs, respectively, of their habitats.

6.1 Alteration of fundamental ecosystem structures and processes
Plants form the biological foundation of all terrestrial and aquatic communities. Therefore, mass invasions of alien plants more or less cause structural andfunctional changes in ecosystems, including alterations in nutrients and/or structural conditions (Schmitz
et al., 1997). Particularly, changes in dominant plant
species may lead to the replacement of dominant plant
consumers, followed by their predators, and further
cause a chain of changes in species compositions at
every trophic level, and thus disrupt food webs andother structural and functional features of the ecosystem.
Even if the invasive species are pioneers dominating only early phases of the vegetation succession sere,
the effects of the invasion may last long through persistent soil seed banks. Invasive alien plant species,
when once established in an ecosystem, may cause
irreversible changes by producing large seed sources
above and/or under the soil surface (Harper, 1977;
Thompson & Grime, 1977; Thompson, 2000). Soilseed bank strategies, using long persistent seeds andphysiological mechanisms to detect temporal ‘safe
sites’ for seedling establishment are common to mostinvasive alien species established in Japan (Washitani& Morimoto, 1993; Washitani, 2002). Two of the major families contributing to the invasive alien herbaceous flora of Japan are the Compositae and Graminae,
the former being well characterized by highly dispersible aerochorous seeds and/or long-lived seeds
that tend to be persistent in soil seed banks. Contemporary surface soils of various habitats of Japan, including wetlands, woodlands, plantations, floodplains
and farmlands have more or less accumulated viable
seeds of such alien plant species, even if theabove-ground vegetation contains no or few alienplant species (Table 1).
Some invasive plants predominating in the riparianvegetation, such as Ambrosia trifida have large seeds
with low specific gravities, which are apparently lessmobile, but can move freely in riparian habitats with
abundant persistent and temporary watercourses channeling hydrochorous seed dispersal.
Flourishing invasive alien plants furnished withstrategies enhancing spatial and temporal dispersal ofseeds inevitably cause alteration of the early stages ofsuccession seres. This is likely to be one of the mostconspicuous influences of plant invasions on ecosystem processes. When modern plant ecological studies
on floristic succession in Japan started in the 1960s,
plants predominating in the early stages of secondary
succession had already been replaced by North
American plants such as Ambrosia altesiaefolia var.
elatior, Erigeron annuus, and E. canadensis (Numata
et al., 1964). Accumulation of persistent soil seed

Invasive Alien Species Problems in Japan: an Introductory Ecological Essay

5

Table 1 Nonindigenous plant species found in the soil seed bank of various habitats in Japan (compiled according to Washitani,
2002, and Ajima, 2001)
occurrence ofnonindigenous species
major nonindigenous
species

percentage percentage
total
in seedin species species
numbers
numbers number

sampledarea(m2)

methodstudy sitereferences

Bidens frondosa, Eclipta
thermalis

0.2

9.1

22

1.6

seedling
emergence

riparian woodland(Kokai River)

Imahashi &Washitani (1996)

Eclipta thermalis,
Lindernia dubia

9.6

13.9

36

1.6

seedling
emergence

moist tall grassland(Kokai River)

Imahashi &Washitani (1996)

Lindernia dubia, Erigeron
annuus

13.2

11.1

27

3.0

seedling
emergence

abandoned paddy(Ibaraki Prefecture)

Koshimizu et al.
(1997)

Erigeron philadephicus,
Cerastium glomeratum

48.7

40.9

23<

2.8

seedling
emergencedredged soil (Lake
Kasumigaura)

Ikeda et al.
(1999)

Phytolacca americana

1.9

3.3

30

0.3

directcounting

Japanese cedar
Ajima et al.
plantation (Kamaishi (2000)
City)

Conyza sumatrensis,
Erigeron philadephicus

8.7<

14.4

99

2.4

seedling
emergencecoppice woodland(Tokyo Metropolitan)

Crassocephalum
crepidioides, Conyza
sumatrensis

37.4

6.7

30

0.4

direct count- secondary deciduous Nakagoshi
ing and seed- woodland (Kobe(1981)
ling emerCity)
gence

Phleum pratense,
Trifolium repens

45.5

63.6

11

0.7

floating
methodSasa grassland(Hokkaido Prefecture)

Tsuyuzaki &Kanda (1996)

Anthoxanthum odoratum

0.2

5.0

20

0.1

direct counting

Zoysia grassland(Aomori Prefecture)

Hayashi &Numata (1971)

Trifolium repens, Poa
pratensis

52.9

4

33

0.3

direct counting

maritime grassland(Hokkaido Prefecture)unpublished databanks of alien ruderal and pioneer species has increased since then and the contemporary surface soil
in various habitats with intense human intervention
contains profuse seed banks of North American plants
including Erigeron, Solidago, and Oenothera species(Ajima, 2001; Ikeda et al., 1999).
Once a persistent soil seed bank of an invasive species has been established, either natural or human disturbances will always bring about the domination of
the alien species, which will further replenish the soil
seed bank or enlarge the seed sources of the invasive
species.
6.2 Changes in habitat conditions
The habitats most profoundly affected by alienplant species in Japan may be riparian floodplains andfresh aquatic habitats (Miyawaki & Washitani, 2004).
Generally, invasive legume plants that are capable ofnitrogen fixation with the aid of symbiotic bacteria
tend to enhance soil fertility in originally infertile
habitats (Schmitz et al., 1997). Nutrient poor substrates of gravelly floodplains characterized by specific sparse vegetation along rapid Japanese rivers arelikely to be increasingly enriched by invasion of
Robinia pseudoacacia from North America, and thus
subsequent weedy plant invasions are facilitated(Miyawaki & Washitani, 2004).
Alien pasture grasses that have been extensively

Hamada &Kuramoto (1994)

introduced into various construction work sites
throughout Japan for the purpose of erosion prevention such as Eragrostis curvula and Festuca
arundinacea have established tremendous seed
sources everywhere, especially in mountainous regions (Washitani, 2001). These introduced grasses arehighly invasive and if riparian habitats are invaded,
the substrate condition of gravelly floodplains can bechanged into sandy/silty conditions, because bunchesof these grasses tend to trap sand and silt during flooding (Nakatsubo, 1997; Muranaka & Washitani, 2001a).
Thusly altered substrate conditions facilitate the establishment and growth of weedy plants including thosegrasses themselves, which were totally absent fromthe original gravelly floodplains (Muranaka &Washitani, 2001b). Thus, the original conditions andvegetation of gravelly floodplains, i.e., sparse vegetation cover consisting principally of riparian endemics
growing in gravelly-sandy conditions, are being lost
rapidly (Muranaka & Washitani, 2003). The competitive alien plants exclude less competitive indigenous
plants adapted to infertile substrate conditions of theflood plain, and the replacement of dominant plants aswell as the alteration of species compositions will
inevitably result in profound changes to the wholecommunity through changes in the composition ofmajor herbivorous animal species.

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6.3 Predation and herbivory
Consumption by invasive species with rapidly
growing populations has tremendous effects on the
populations of native prey animals or food plant species. Predation by introduced animals is one of themost serious factors elevating the risk of extinction ofrare endemic species in the biodiversity hotspots ofJapan, the Ogasawara Islands and the Okinawa Islands(Nonindigenous Species Committee, 2002).
One of the most notorious introduced mammal
predators threatening endangered species is the Javamongoose introduced into the Okinawa Islands for thecontrol of poisonous snake, Trimeresurus flavoviridis,
and/or rats (Yamada, 2001, 2002). The introduced
Java mongoose preys on various native mammals,
ground-nesting birds, amphibians and reptiles, threatening them critically in the Yanbaru (northern) regionsof Okinawa Island and Amami-Ohshima Island(Yamada, 2002; Yamada & Sugimura, 2004).
In the Yanbaru region of Okinawa Island, the rangeof the endangered species Ralus okinawae has been
reduced northwardly at a rate of approximately 1 km
per year (Tanahara, 2002), probably because of Javamongooses. A control program was started in 2000,
aiming at preventing the invasion from proceeding
further north into an area recognized as one of theprominent hotspots for biodiversity of Japan. A
national mongoose eradication program has been
started recently on Amami-Ohshima Island (Yamada& Sugimura, 2004) where the mongoose threatens
many rare and/or endemic mammals and birds such as
the Amami black rabbit (Pentalagus furnessi), Ryukyu
spiny rat (Tokudaia osimensis osimensis) and Amami
Woodcock (Scolopax mira) (Yamada 2002).
Anolis carolinensis has been naturalized in the
Ogasawara Islands, the fauna of which is characterized by extremely high endemism. Its range is rapidly
expanding to cover large tracts of the main islands of
the Ogasawaras (Hasegawa, 1988), and a wide range
of insects and animals, including an endangered native
lizard (Cryptoblepharus boutonii nigropunctatus),
have become critically threatened (Suzuki & Nagoshi,
1999). In the range where A. carolinensis has alreadyinvaded, endemic insects including dragonflies, small
beetles, and woodborers have totally disappeared(Karube, 2001). Predation by A. carolinensis is suspected to be principally responsible for the disappearance of various endemic insects, since the intact insect
fauna and community are still preserved on Anijima
Island, which has still avoided invasion by A.
carolinensis (Karube, 2002).
As a result of heavy herbivory by the introduced
Chinese fish (Ctenopharhyngodon idellus), aquaticplants are locally extinct in Lake Nojiri and Lake
Kizaki in Nagano Prefecture. C. idellus is known to
eat greedily every aquatic plant including emergent
ones such as reeds and cattails (Hayashi, 2002) anddenude natural aquatic vegetation along shorelines(Tachikawa, 2002).

Bluegill introduced from North America, which are
one of the commonest fishes in every type of freshwater ecosystem of contemporary Japan, are one of themost influential invasive alien species because of theirwide prey range (Nakai, 2002a). In Japan, naturalized
bluegill prey on eggs and flies of a wide range offishes, and exert strong negative effects on native fish
fauna in various freshwater ecosystems (Azuma,1992). Dietary planktivorous, benthivorous and herbivorous specialization closely associated with morphological differentiation suggests adaptive divergence during a relatively short period of several decades from the colonization of the species in Japaneselakes (Yonekura et al., 2002). This species has become
the most predominant fish species in various freshwater ecosystems in Japan, including Lake Biwa andLake Kasumigaura (Nakai, 2002b).
A number of islands among the Ogasawaras andSouthwestern Islands have experienced devastating
damage to vegetation by naturalized goats, whichwere abandoned due to changes in human eating habits and/or drastic human population loss from the remote island areas during the period of rapid economic
development (Tokita, 2002). On semi-tropical islands
such as the Ogasawaras, denudation of vegetation bygoats causes secondary and tertiary effects such as
extensive soil erosion and damage to coral by sedimentation of the eroded soil (Tokita, 2002).
6.4 Replacement through competition
A strong competitor monopolizes resources andexcludes less competitive species from the habitat. In
contrast with animals, which have diverse prey differing among species, plants depend on a few kinds ofcommon resources for their growth, i.e., light, waterand nutrients. Therefore, competition tends to be severe (Grime, 1979).
Ambrosia trifida, a giant annual plant native to
North America, is highly competitive and grows on
fertile soils (Bazzaz, 1968; Sickels & Simpson, 1985).
Its original habitat is delta floodplains (Sickels &Simpson, 1985), but the species invaded into manmade nutrient rich habitats to become a notorious
weed of soybean fields in the USA. As mentioned previously, the species was presumably introduced
intermingled in soybean crops imported from the USA
to Japan. Competitive exclusion by this species causing a decrease in plant species diversity was suspected
at nature reserve of moist tall grasslands along the
Arakawa River near Tokyo, where plant species diversity was negatively correlated with the abundance of A.
trifida (Miyawaki & Washitani, 1996).
Competitive exclusion of native bumblebees byBombus terrestris, which has become naturalized inseveral regions of the world after commercial introduction as a greenhouse pollinator, has been suggested(Dafni & Shmida, 1996; Hingston & McQuillan,
1998). Also in the Hidaka region of Hokkaido, B.
terrestris is suspected to be competitively replacing
native bumblebees at this time according to the resultsInvasive Alien Species Problems in Japan: an Introductory Ecological Essayof continuous monitoring by a number of volunteers
including scientists and citizens (Matsumura et al.
2004). The monitoring, performed in an area where
greenhouse tomatoes are cultivated, widely suggeststhat B. terrestris had become dominant in the bumblebee fauna by 2003 (Matsumura et al., 2004).
The introduced omnivorous turtle, Trachemus
scripta elegans, which probably has already become
one of the most common turtles in Japan (NACS-J,
2004), preys on an extremely wide range of animals
and plants including fish, amphibians, shrimp, shellfish, aquatic plants and the leaves, flowers and fruitsof land plants, and has higher reproductive fertility
even under various environmental stresses (Yasukawa,
2002). Competitive exclusion of native common turtles is suspected. However, investigation into the effects of the species on the ecosystem has yet to be performed, though strong impacts on regional biodiversity and aquatic ecosystems are suspected (Yasukawa,
2002).
6.5 Parasite or disease transmission
The felid virus disease AIDS FIV was detected in
an adult male wild lynx, Felis bengalensis euptilura,
which is endemic to Tsushima Island of Nagasaki Prefecture, western Kyusyu, and is now highly endangered (Akuzawa, 2002). It is suspected that house catstransferred AIDS FIV to the wild lynx through biteson the occasion of fighting.
Pathogenic flukes parasitic to freshwater fishes,
Parabucephalopsis parasiluri, have been transmitted
from a bivalve species (Limnoperna fortunei), anintermediate host of the parasite, to native fishes of
the carp family (Urabe, 2002). The bivalve species
was unintentionally introduced from China. During
the winter from December 1999 to January 2000, an
epidemic caused by the fluke swept through theriparian system originating from Lake Biwa, and avast number of native fishes of carp family, especially
the Oikawa carp (Zacco platypus) were killed (Urabe,2002).
Intentionally introduced insects, including Bombus
terrestris as a commercial pollinator and stag beetles
as pet insects, have been revealed to carry various
pathogenic agents including mites, the transmission ofwhich to native insects through naturalization of these
insects is a serious concern (Goka et al., 2001; Goka,
2002, 2004).
6.6 Hybridization or interference with reproduction
The Japanese monkey (Macaca fuscata) has themost northerly range among primates except for
Homo sapiens (Kuroda, 1998). The Taiwan monkey(M. cyclopis) has established populations on the
Shimokita Peninsula, Izu-Ohshima Island, and the Kii
Peninsula after World War II as the result of abandonment of zoo individuals (Nakaya & Maekawa, 2002).
On the Kii Peninsula the range of the populations of
the Taiwan monkey have begun to overlap with that ofa population of M. fuscata (Wakayama Prefecture,72000), and hybridization between these species is now
in progress (Nakaya & Maekawa, 2002). In order topreserve a pure linage of Japanese monkeys, the prefectural government decided to exclude hybrid individuals.
Rhodeus ocellatus ocellatus, which was unintentionally introduced through intermingling with the fryof Hypophthalmichthys molitrix imported from China
as a fishery resource, has become established in fresh
aquatic ecosystems through range expansion facilitated by human activities of stocking lakes and rivers(Nagata, 1980). R. ocellatus ocellatus has hybridized
with Rhodeus ocellatus kurumeus, which was once
widely distributed in western Japan but has now become endangered (Environment Agency of Japan,1999). Hybridization with R. ocellatus ocellatus isassumed as the main cause of the threat.

7. Impacts on Human Life and Health
7.1 Influences on industries
Agriculture is the industry most strongly affectedby alien pests and weeds. It is no exaggeration to saythat in present-day Japan, almost all the influential
pests are alien species (Kiritani, 2002; Shimizu, 2002;
Kiritani & Morimoto, 2004). The rice water weevil,
Lissohhoptrus oryzophilus, which is currently themost serious insect pest of rice crops, originated fromthe USA, was first found in Aichi Prefecture in 1976,
and expanded its range through the 1990s when a vast
tract of Japanese paddies was infested (Kiritani &Morimoto, 2004).
Japanese forestry has also been affected by invasive alien species, as markedly illustrated by pine wilt
disease caused by a pathogenic nematode originatingfrom North America, Bursaphelenchus xylophilus. A
mutualistic relationship between the nematode killing
the pine trees and the Japanese pine sawyer (Monochamus alternatus), carrying the nematode and feeding on the trees infected by the nematode, was established after the nematode invasion and has been responsible for the rapid range expansion and heavy
damage to pine plantations (Kiritani & Morimoto,2004). Aerial spraying of insecticides, which has been
the major control measure against the pests, might
seriously affect local biodiversity.
Dense applications of chemicals for agricultural/forestry pest control are secondary but crucial
consequences of alien pest invasions. Chemical application to agricultural lands is suspected as one of the
major causes of soil and/or water pollution in present-day Japan (Ando, 1990).
Freshwater fisheries are also highly vulnerable tobiological invasion. Japanese freshwater fishing is an
occupation with a long-held tradition at least from the
Neolithic Age, but is facing a crisis of collapse. Oneof the factors responsible for the crisis is invasive
alien fish such as large-mouth bass and bluegill, whichhave explosively increased after introduction and ad-

8

I. WASHITANI

aptation to Japanese freshwater environments andheavily consume native fishes (Nakai, 2000). Together
with other factors such as water pollution, eutrophication and destruction of terrestrial-aquatic ecotone
vegetation, these invasive alien fishes seriously
threaten Japanese freshwater fisheries and also Japanese food culture with a long tradition (Kawanabe,
2000).
Also in coastal regions, a number of invasive alien
species affect fish farms. A representative case is thesevere damage to oyster culture by the sedimentary
annelid Hydroides ezoensis in the Seto inland sea,
with the yearly total damage amounting to several
billions of yen (Nishi, 2002).
Limnoperna fortunei is a bivalve native to China,
and introduced into Japan unintentionally intermingled with imported corbicula in the 1980s (Matsuda &Nakai, 2002). The species has a habit of adhering witha proteinaceous fibrous excretion to solid materials
such as stone and wood, and amassing thickly on concrete walls, obstructing water inlets of hydropower
plants or water supply facilities.
7.2 Influences on human healthSome alien plants are major causes of pollinosis.
Pollinosis, which is also called hay fever, is seasonallyrecurrent bouts of sneezing, nasal congestion, andtearing and itching of the eyes caused by allergies tothe pollen of certain plants including alien Ambrosia
species from North America and alien meadow
grasses such as Lolium multiflorm, L. perenne, L. x
hybridum, and Dactylis glomerata (Koizumi, 1998;
Saito & Ide, 1994). In contrast to continental areas
covered by large tracts of dry grasslands, in prewesternized Japan, pollinosis would have been rather
exceptional, since human residential areas wereembedded in fine-grained landscape mosaics of woodland with various trees, paddies and grasslands, where
no single species with anemophilous pollen dominatedoverwhelmingly.
In Japan, pollinosis was first recognized as an earlysummer hay fever caused by Ambrosia species in theearly 1960s (Araki, 1960; Saito, 1996). It became
prevalent first among school children during a boomin school swimming pool construction during those
years. The disease, with symptoms similar to influenza, was misunderstood as an epidemic and wascalled ‘pool fever.’ More recently, a very high incidence of pollinosis has been reported for school children in an area adjacent to the Edo River flowing
through Tokyo, the banks of which are dominated byalien grasses, especially Lolium species (Parent grouplearning on grass pollinosis, 1999).

8. Growing Public Concern and Activities
toward Establishing an Effective Legal
SystemUntil quite recently, Japanese have felt little concern about biological invasion. However, very recently,

public attitudes toward introduced species began tochange, as concern about environmental issues including biological invasion has rapidly grown after substantial losses of national biodiversity and ecosystem
integrity due to invasive alien species and other related problems mentioned above.
An opinion poll on ‘public attitudes to nature
conservation’ conducted by the Cabinet Office of theJapanese Government in the spring of 2001 (Cabinet
Office, 2001a) revealed that more than 85% of respondents to the questionnaire approve of the need forsome restrictive measures against introduction of
non-native species and those approving of eradicationof alien species badly influencing ecosystems accounted for more than 70% of respondents. The needto manage introduced species has gradually become
understood among the public.
In December 2001, in a report submitted to thePrime Minister, the Council for Regulatory Reform of
the Cabinet Office recommended urgent investigations
aiming at quick establishment of national legal regulatory systems to respond to domestic biological invasion problems, including regulations on the importation and utilization of introduced species and mechanisms for the management of invasive alien species
which have already naturalized (Cabinet Office,2001b). Responding to the Council’s request, theNatural Environment Bureau of the Ministry ofEnvironment started an investigation on the status ofand necessary measures against invasive alien species,
and formulated a policy for quick establishment of aneffective legal system against invasive alien species
problems. In May 2004, a new national regulation
against invasive alien species, i.e., the Invasive Alien
Species Act was promulgated.
Reference
Ajima, M. (2001) Accumulation of seeds of exotic species inthe soil seed bank in Japan. Japanese Journal of Conservation Ecology, 6:155-165. (in Japanese)
Ajima, M., S. Tsuda and A. Hiratsuka (2000) Changes in species composition and density on soil seed bank after a wildfire at a Cryptomeria japonica forest in Kamaishi, northeastern Japan. Vegetation Science, 17:15-21. (in Japanese withEnglish abstract)
Akuzawa, M. (2002) Wild cat and FIV infection. In: The Ecological Society of Japan, ed., Handbook of Alien Species inJapan, Chijin-Shokan, Tokyo, pp.222-223. (in Japanese)Ando, M. (1990) For Understanding Pesticide Pollution. Godo
Publishing. (in Japanese)
Araki, H. (1960) Investigation on pollinosis: Seasonal variationin aerial pollen. Allergy, 9:648-655. (in Japanese)
Araya, K. (2002) Stag beetles and beetles. In: The EcologicalSociety of Japan, ed., Handbook of Alien Species in Japan,
Chijin-Shokan, Tokyo, pp.158-159. (in Japanese)
A round-table conference on alien fish problems (2003)
Counter-measures by stakeholders against problems of alienfish such as largemouth bass: an intermediate report of around-table conference on alien fish problems. (in Japanese)
Asao, N. (1998) National seclusion. In: CD-ROM World Encyclopedia ver. 1.2, Hitachi Digital Heibonsha, Tokyo. (in Japa-

Invasive Alien Species Problems in Japan: an Introductory Ecological Essay
nese)
Azuma, M. (1992) Ecological release in feeding behaviour: thecase of bluegills in Japan. Hydrobiologia, 243/244: 269-276.
Bazzaz, F. A. (1968) Succession on abandoned fields in the
Shawnee Hills, Southern Illinois. Ecology, 49: 924-936.
Cabinet Office (2001a) Report on Opinion Poll on Nature Conservation. Cabinet Office. (in Japanese)
Cabinet Office (2001b) First Report Regarding Promotion ofRegulatory Reform. Prepared by the Council for Regulatory
Reform, Cabinet Office. (in Japanese)
Carlton, J. T. (1985) Transoceanic and interoceanic dispersal ofcoastal marine organisms: the biology of ballast water.
Oceanography and Marine Biology, Annual Review, 23:313-371.
Carlton, J. T. (2001) Global change and biological invasions in
the oceans. In: R. J. Hobbs and H.A. Mooney, eds., Invasive
Species in a Changing World, Island Press, Washington,
pp.31-53.
Chinzei, K. (1991) Late Cenozoic zoogeography of the Sea ofJapan. Episodes, 14:231-235. (in Japanese)
Dafni, A. and A. Shmida (1996) The possible ecological implications of the invasion of Bombus terrestris L. (Apidae) at
Mt Carmel, Israel. In: A.C. Matheson, ed., The Conservationof Bees, The Linnean Society of London and The International Bee Research Association, London, pp.189-200.
Ecological Society of Japan (2002) Handbook of Alien Species
in Japan, Chijin-shokan, Tokyo. (in Japanese)
Environmental Agency of Japan (1999) National Red List ofFreshwater and Blackish Water Fishes. Environmental
Agency of Japan, Tokyo. (in Japanese)
Environmental Bureau Tokyo Metropolis (2002) Water environment in the Tokyo Bay.
Furota, T. (1996) Life cycle studies on the introduced spider
crab Pyromaia tuberculata (Lockington) (Brachyura:
Majidae). II. Crab stage and reproduction. Journal of Crustacean Biology, 16: 77-91. (in Japanese)
Furota, T. (2002) Tokyo Bay. In: The Ecological Society ofJapan, ed., Handbook of Alien Species in Japan,
Chijin-Shokan, Tokyo, 274 p. (in Japanese)Goka, K. (2002) Parasitic mites from imported insects. In: The
Ecological Society of Japan, ed., Handbook of Alien Species
in Japan, Chijin-Shokan, Tokyo, pp.217-129. (in Japanese)Goka, K. (2004) Biological invasion caused by commercialization of stag beetles in Japan. Global Environmental Research,
8(1): 67-74.
Goka, K., K. Okabe, M. Yoneda and S. Niwa (2001) Bumblebee commercialization will cause worldwide migration ofparasitic mites. Molecular Ecology, 10: 2095-2099
Gomi, T. (1995) Effect of temperature on diapause response tophotoperiod in Hyphantria cunea with special reference tolocal divergence. Applied Entomology and Zoology, 30:
490-492.
Grime, J.P. (1979) Plant Strategies and Vegetation Process.
Wiley, New York.
Hamada, H. and N. Kuramoto (1994) A study of seed bank in
Quercus serrata forest by surveying seedling emergence andits application to forest management. Journal of the JapaneseInstitute of Landscape Architecture, 58: 76-82. (in Japanese)
Harper, J.L. (1977). Population Biology of Plants. Academic
Press, London.
Hasegawa, M. (1988) Range expansion of Anolis carolinensis
on Chichi-jima, the Bonin Islands, Japan. Japanese Journalof Herpetology, 12:115-118.
Hayashi, H. (2002) Lakes of Shinsyu, Nagano Prefecture. In:
The Ecological Society of Japan, ed., Handbook of Alien
Species in Japan, Chijin-Shokan, Tokyo, pp.262-264. (inJapanese)
Hayashi, I. and M. Numata (1971) Viable buried-seed population in the Miscanthus – and Zoisia type grasslands in Japan.

9– Ecological studies on the buried-seed population in the soil
related to plant succession VI -. Japanese Journal of Ecology,
20:243-252. (in Japanese)
Hingston, A.B. and P.B. McQuillan, (1998) Does the recently
introduced bumblebee Bombus terrestris (Apidae) threaten
Australian ecosystems? Australian Journal of Ecology,
23:539-549.
Ikeda, T. (2002) Racoon. In: The Ecological Society of Japan,
ed., Handbook of Alien Species in Japan, Chijin-Shokan,
Tokyo, pp.70. (in Japanese)
Ikeda, Y., S. Araki, T. Muranaka and I. Washitani (1999) Possibility of using dredged mud as material for vegetation restoration. Journal of Conservation Ecology, 4:21-31. (in Japanese)
Imahashi, M. and I. Washitani (1996) Evaluation of soil seedbanks as plant materials for the restoration of floodplain
vegetation. Japanese Journal of Conservation Ecology,
1:131-147. (in Japanese)
Ito, K. and M. Miyahara (1984) Inheritance in Erigeron philadelphicus L. Weed Research Japan, 29: 301-307.
Iwasaki, K. (2002) Osaka Bay. In: The Ecological Society ofJapan, ed., Handbook of Alien Species in Japan,
Chijin-Shokan, Tokyo, 275 p. (in Japanese)
Karube, H. (2001) On the crisis of dragonflies endemic to
Ogasawara Islands. Monthly Journal of Insects, 369:22-32.
(in Japanese)
Karube, H. (2002) Predatory impact on endemic insects by thegreen anole in the Ogasawara Islands. In: The EcologicalSociety of Japan, ed., Handbook of Alien Species in Japan,
Chijin-Shokan, Tokyo, 241 p. (in Japanese)
Kawanabe, H. (1980) Rainbow trout, Onchrhynchus mykiss. In:
T. Kawai, H. Kawanabe and H. Mizuno, eds., Freshwater
Organisms in Japan: Their Ecology of Invasion and Disturbance, Tokai University Press, Tokyo, pp. 44-48. (in Japanese)
Kawanabe, H. (2000) Fish Eating History: How Japanese havebeen Eating Fishes from Ancient Ages. Heibonshya, Tokyo.
(in Japanese)
Kiritani, K. (2002) Invasion routes of pests: conflicts between
free trade and plant quarantine. In: The Ecological Society ofJapan, ed., Handbook of Alien Species in Japan,
Chijin-Shokan, Tokyo, pp.52-53. (in Japanese)
Kiritani, K. and N. Morimoto, (2004) Invasive insect andnematode pests from North America. Global Environmental
Research, 8(1): 75-88.
Kitano, S. (2004) Ecological impacts of rainbow, brown and
Brook trout in Japanese inland waters. Global Environmental
Research, 8(1): 41-50.
Kodansha International (ed.) (1999) The Kodansha Bilingual
Encyclopedia of Japan. Kodansha International Ltd., Tokyo.
Koizumi, K. (1998) Pollinosis. In: CD-ROM World Encyclopedia ver. 1.2, Hitachi Digital Heibonsha, Tokyo. (in Japanese)
Koshimizu, A., S. Araki, I. Washitani, Y. Hioki, T. Tanaka and
M.Osada (1997) Evaluating the soil seed bank of an abandoned valley paddy field as materials for vegetation restoration. Japanese Journal of Conservation Ecology, 2:189-200.
(in Japanese)
Kuroda, M. (1998) Japanese monkey. In: CD-ROM World
Encyclopedia ver. 1.2, Hitachi Digital Heibonsha, Tokyo. (inJapanese)
Matsuda, S. and K. Nakai (2002) Limnoperna fortunei. In: The
Ecological Society of Japan, ed., Handbook of Alien Species
in Japan, Chijin-Shokan, Tokyo, 173 p. (in Japanese)
Matsumura, C., J. Yokoyama and I. Washitani (2004) Invasion
status and potential ecological impacts of an invasive alien
bumblebee, Bombus terrestris L. (Hymenoptera Apidae)
naturalized in southern Hokkaido, Japan. Global Environmental Research, 8(1): 51-66.
Ministry of Agriculture, Forestry and Fisheries (2001) Trade

10

I. WASHITANI

Report on the Products of Agriculture, Forestry and Fisheries. Ministry of Agriculture, Forestry and Fisheries. (in Japanese)
Miyamoto, A., N. Tamura, K. Sugimura and F. Yamada (2004)
Predicting habitat distribution of the alien Formosan squirrel
using logistic regression model. Global Environmental Research, 8(1): 13-21.
Miyawaki, S. and I. Washitani (1996) A population dynamics
model for soil seedbank plant and its application to the prediction of the effects of weeding on a population of Ambrosia
trifida L. invading into a nature reserve. Japanese Journal ofConservation Ecology, 1:25-47. (in Japanese)
Miyawaki, S. and I. Washitani (2004) Invasive alien plant species in riparian areas of Japan: the contribution of agricultural weeds andrevegetation species. Global Environmental
Research, 8(1): 89-101.
Murakami, O. and I. Washitani (2002) The legal system. In:
The Ecological Society of Japan, ed., Handbook of Alien
Species in Japan, Chijin-Shokan, Tokyo, pp.11-14. (in Japanese)
Muranaka, T. and I. Washitani (2001a) Alien plant invasions
and gravelly floodplain vegetation of the Kinu River. Ecology and Civil Engineering, 4:121-132. (in Japanese)
Muranaka, T. and I. Washitani (2001b) Invasion of alien grass
Eragrostic curvula on the gravelly floodplains of the Kinu
River and decrease of river endemics: Necessity of pungent
measures. Japanese Journal of Conservation Ecology,
6:111-122. (in Japanese)
Muranaka, T. and I. Washitani (2002) Eragrostis curvula. In:
The Ecological Society of Japan, ed., Handbook of Alien
Species in Japan, Chijin-Shokan, Tokyo, p.199. (in Japanese)
Muranaka, T. and I. Washitani (2003) The population
expansion predicted by a simulation model of an invasive
alien species, Eragrosits curvula, in a middle-reachfloodplain. Japanese Journal of Conservation Ecology,
8:51-62. (in Japanese)
NACS-J (2004) Nationwide turtle survey.
Nagata, Y. (1980) Rhodeus ocellatus ocellatus. In: T. Kawai,ed., Japanese Fresh-Aquatic Organisms: Biology of Invasion
and Disturbance, Tokai University Publishing, Hadano,
pp.147-153. (in Japanese)
Nakagoshi, N. (1981) Notes on the buried viable seeds in soils
of forest communities on Mt. Futatabi, Kobe. Studies on
Vegetation and Soil of the Permanent Nature Reserve Area in
Mt. Futatabi, Kobe. Report of the Second Investigation, pp.
69-94. (in Japanese)
Nakai, K. (2000) Background and present status of alien
species problems among freshwater fishes in Japan: toward
the future management. Japanese Journal of Conservation
Ecology, 5:171-180. (in Japanese)
Nakai, K. (2002a) Bluegill. In: The Ecological Society of Japan,
ed., Handbook of Alien Species in Japan, Chijin-Shokan,
Tokyo, 119 p. (in Japanese)
Nakai, K. (2002b) Lake Biwa. In: The Ecological Society ofJapan, ed., Handbook of Alien Species in Japan,
Chijin-Shokan, Tokyo, pp.265-268. (in Japanese)
Nakakita, H. (2002) Exotic weevils. In: The Ecological Societyof Japan, ed., Handbook of Alien Species in Japan,
Chijin-Shokan, Tokyo, p.134. (in Japanese)
Nakatsubo, T. (1997) Colonization of invasive grasses in a riverfloodplain: its impact on the riparian plant community.
Japanese Journal of Conservation Ecology, 2: 179-187. (inJapanese)
Nakaya, J. and S. Maekawa (2002) Macaca cyclopis. In: The
Ecological Society of Japan, ed., Handbook of Alien Species
in Japan, Chijin-Shokan, Tokyo, 64 p. (in Japanese)
Nishi, E. (2002) Hydroides ezoensis. In: The EcologicalSociety of Japan, ed., Handbook of Alien Species in Japan,
Chijin-Shokan, Tokyo, p.180. (in Japanese)

Nogami, M., T. Koaze and M. Fukuda (1980) Periglacial
environment in Japan: Present and past. GeoJournal, 4:125-132.
Nonindigenous Species Committee (2002) On the Measures for
Nonindigenous Species. Nature Conservation Bureau, Tokyo.
(in Japanese)
Numata, M., I. Aoki and I. Hayashi (1964) Secondary
succession of abandoned fields. Japanese Journal of Ecology,
14: 224-227. (in Japanese)
Parent Group Learning on Grass Pollinosis (1999) Grass
Pollinosis and River Banks of Edo River. Parent Group
Learning on Grass Pollinosis. (in Japanese)
Saito, Y. (1996) Pollinosis by introduced plants. Iden, 40:42-46.
(in Japanese)
Saito, Y. and T. Ide (1994) Science of Pollinosis. Kagaku-dojin,
Tokyo. (in Japanese)
Seino, H. (2002) Import status of alien species. In: The
Ecological Society of Japan, ed., Handbook of Alien Species
in Japan, Chijin-Shokan, Tokyo, pp.9-11. (in Japanese)
Schmitz, D.C., D. Simberloff, R. H. Hofstetter, W. Haller and D.
Sutton (1997) The ecological impact of nonindigenous plants.
In: T.C. Brown, D.C. Schmitz and D. Simberloff, eds.,
Strangers in Paradise: Impact and Management of
Nonindigenous Species in Florida, Island Press, Washington
DC, pp.39-61.
Shimizu, N. (1998) Recent situation of invasion and diffusionof alien weeds and its control. Japanese Journal of Ecology,
48:79-85. (in Japanese)
Shimizu, N. (2002) Harmful weed invasion through feed cereal
import. In: The Ecological Society of Japan, ed., Handbookof Alien Species in Japan, Chijin-Shokan, Tokyo, pp.48-49.
(in Japanese)
Sickels, F.A. and R. L. Simpson (1985) Growth and survival ofgiant ragweed (Ambrosia trifida L.) in a Delaware River
freshwater tidal wetland. Bulliten of Torrey Botanical Club,112: 368-375.
Suda, S. (2002) Large-mouth bass eating dragonflies. In: The
Ecological Society of Japan, ed., Handbook of Alien Species
in Japan, Chijin-Shokan, Tokyo, 121 p. (in Japanese)
Suzuki, A. and M. Nagoshi (1999) Habitat utilization of thenative lizard, Cryptoblepharus boutonii nirgopunctatus inarea with or without the introduced lizard, Anolis caroliensis,
on Hahajima, the Ogasawara Islands, Japan. In: J. Ota, ed.
Tropical Island Herpetofauna: Origin, Current Diversity,
and Conservation, Elsevier Science, Amsterdam,
pp.155-168.
Tachikawa, K. (2002) Asian grass carp. In: The EcologicalSociety of Japan, ed., Handbook of Alien Species in Japan,
Chijin-Shokan, Tokyo, 111 p. (in Japanese)
Tanahara, N. (2002) Measures against mongoose in Amami
Island. In: The Ecological Society of Japan, ed., Handbookof Alien Species in Japan, Chijin-Shokan, Tokyo, pp.20-21.
(in Japanese)
Tanaka, K. (1972) Remodeling the Japanese Archipelago.
Nikkankogyo, Tokyo. (in Japanese)
Thompson, K. (2000) The functional ecology of soil seed banks.
In: M. Fenner, ed., Seeds: the ecology of regeneration inplant communities. 2nd ed., CABI Publishing, London,
pp.215-235.
Thompson, K. and J. P. Grime (1979) Seasonal variation in theseed banks of herbaceous species in ten contrasted habitats.
Journal of Ecology, 67:893-921.
Tokita, K. (2002) Goat: destroyer of island vegetation. In: The
Ecological Society of Japan, ed., Handbook of Alien Species
in Japan, Chijin-Shokan, Tokyo, pp.80-81. (in Japanese)
Togashi, K. (2002) Bursaphelenchus xylophilus. In: The
Ecological Society of Japan, ed., Handbook of Alien Species
in Japan, Chijin-Shokan, Tokyo, 153 p. (in Japanese)
Totman, C. (2000) A History of Japan. Blackwell Publishers,Invasive Alien Species Problems in Japan: an Introductory Ecological Essay
Massachusetts.
Traffic Japan (2002) Status of Animal Import into Japan.
Traffic Japan. (in Japanese)
Tsuyuzaki, S. and F. Kanda (1996) Revegetation patterns andseedbank structure on abandoned pastures in northern Japan.
American Journal of Botany, 83:1422-1428.
Urabe, M. (2002) Parabucephalopsis spp. In: The EcologicalSociety of Japan, ed., Handbook of Alien Species in Japan,
Chijin-Shokan, Tokyo, 216 p. (in Japanese)
Wakayama Prefecture (2000) Reports on the status of Macaca
cyclopis in Wakayama Prefecture. Wakayama Prefecture. (inJapanese)
Washitani, I. (1998) Problems caused by the invasion of
Bombus terrestris from the conservation biological viewpoint.
Japanese Journal of Ecology, 43: 73-78 (in Japanese)
Washitani, I. (2001) Restoring Ecosystems. NHK Publishing,Tokyo. (in Japanese)
Washitani, I. (2002) Age of irreversible changes in ecosystems.
Kagaku, 72:77-83 (in Japanese)
Washitani, I. and N. Morimoto (1993) Alien Plants andAnimals Naturalized in Japan. Hoikusya, Tokyo. (inJapanese).

11

WWF-Japan (1999) Investigation on the Trend of the Trade of
CITES Animals. Tokyo. (in Japanese)
Yamada, F. (2001) Mistake introduction of Harpestes javanicus.
Animals and Zoo, 53:10-13. (in Japanese)
Yamada, F. (2002) Harpestes javanicus. In: The EcologicalSociety of Japan, ed., Handbook of Alien Species in Japan,
Chijin-Shokan, Tokyo, 75 p. (in Japanese)
Yamada F. and K. Sugimura (2004) Negative impact of aninvasive small Indian mongoose Herpestes javanicus on
native wildlife species and evaluation of a control project inAmami-Ohshima and Okinawa Islands, Japan. Global
Environmental Research, 8(2). (in press)
Yasukawa, Y. (2002) Chrysemys scripta elegans. In: The
Ecological Society of Japan, ed., Handbook of Alien Species
in Japan, Chijin-Shokan, Tokyo, p.97. (in Japanese)
Yodo, T. (2002) Large mouth bass. In: The Ecological Societyof Japan, ed., Handbook of Alien Species in Japan,
Chijin-Shokan, Tokyo, 117 p. (in Japanese)
Yonekura, R., K. Nakai and M. Yuma (2002) Trophic
polymorphism in introduced bluegill in Japan. EcologicalResearch, 17: 49-58.

(Received 24 February 2004, Accepted 26 April 2004)