Pacific Science (1984), vol. 38, no. 2
© 1984by the University of Hawaii Press. All rights reserved
The Extinction of Endemic Species by a Program of Biological Control!
BRYAN CLARKE,2 JAMES MURRAY,3 AND MICHAEL S. JOHNSON4
ABSTRACT: Land snails ofthe genus Partula, inhabiting the high islands ofthe
Pacific Ocean, have provided exceptional opportunities for studies oil the origin
and differentiation ofspecies: The endemic taxa ofMoorea, in French Polynesia,
have been particularly well studied.
In an attempt to control the numbers of the giant African snail, Achatina
fulica, which is an agricultural pest, a carnivorous snail, Euglandina rosea; has
been introduced into Moorea. It is spreading across the island at the rate ofabout
1.2 km per year, eliminating the endemic Partula. One species is aiready extinct
in the wild; and extrapolating the rate of spread of Ezigltmdina, it is expected that
all the remaining taxa (possibly excepting P. exigua) will be eliminated by
1986-1987.
Euglandina has been introduced into many other oceanic .islands, and it
appears that more than a hundred endemic species are at risk. These observations
point to a serious danger in programs of " biological control."
SINCE THE TIME OF DARWiN, the endemic
species of oceanic islands have held a special
interest for students of evolution.
Archipelagos of volcanic origin, such as the
Galapagos and Hawaiian islands, are natural
laboratories in which the phenomena ofspeciation
can be studied (Lack 1947, Carson and
Y60n 1982). The fauna and flora of such islands
are, however, unusually susceptible to
the introduction of competitors, parasites,
and predators.
In this paper we report the progressive extinction
of land sna ils (genus Partulai , endemic
to the island of Moorea in French
I Manuscript accepted 10January 1984.
2 Museum National d'Histoire Naturelle et Ecole
Pratique des Hautes Etudes en Polynesie Francaise,
Centre de l'Environnernent de Moorea, B.P. 12, Moo rea,
French Polynesia. Permanent address: University of
Nottingham, Department of Genetics, University Park ,
Nottingham NG7 2RD, England.
3 Museum National d'Histoire Naturelle et Ecole
Pratique des Hautes Etudes en Polynesie Francaise,
Centre de l'Environnement de Moorea, B.P. 12, Moorea,
French Polynesia. Permanent address: University of
Virginia, Department of Biology, Charlottesville, Virginia
22901.
4 University of Western Australia, Department of
Zoology, Nedlands, Western Australia 6009.
Polynesia, by an introduced molluscan predator
(Euglandina rosea (Ferussacj),
The classic studies of Crampton (1932) and
later investigations (Murray and Clarke 1980,
Murray, Johnson , and Clarke 1982) have
shown that these snails provide exceptional
opportunities for study of the origin and differentiation
of species. Their unique combination
of ovoviviparity, low mobility, short
generation tim e, ease of culture in the laboratory,
and extensive genetic po lymorphism
(at both the morphological and molecular
levels) make them almost idea l material for
the study of ecological and evolutionary
genetics.
Their loss is not merely a tragedy for students
ofgenetics, it is also a wattling about the
potentially devastating effects of some progra
ms in "biological control"; and it exemplifies
a threat to more than a hundred other
species. Because the Partula of Moorea ha ve
been mapped in great detail, we ar e able to
document rather precisely the progress of
extinction.
98 PACIFIC SCIENCE, Volume 38, April 1984
FIGURE I. The island of Moorea, showing the principal topographical features.
Pacific Ocean. The island isvolcanic in origin, and P. mirabilis Crampton). Their status as
and its age is approximately 1.2 million years good biological species is, however, in ques(Jackson
1976). It isabout 12km in diameter, tion because each, at some point on the island,
and its highest peak rises to 1207 m. Nine gives evidence of hybridization or intergraother
peaks exceed 700m (Figure 1). dation with another. For example, P. tohiveana
Crampton (1932) and Crampton and tohiveana and P. suturalis are the sympatric
Cooke (1953) described eleven species of terminal elements of a ring-species including
Partula, all endemic to the island. Two of P. tohiveana olympia. The pattern is such that,
these (Partula solitaria Crampton and Partula potentially at least, genes could flow from any
diaphana Crampton and Cooke) have since one "species" to any other (with the possible
been relegated to the genus Samoana (Kondo exception of P. mooreana). Nonetheless, at
1973). Of the remaining nine, one (P. den- any particular place as many as four of the
droica Crampton) is clearly a geographical taxa may coexist without interbreeding.
race of P. suturalis Pfeiffer and another (P. When they do so, they are clearly distinct in
olympia Crampton) a geographical race of P. genetics, morphology, ecology, and behavior
tohiveana Crampton (Clarke and Murray (Johnson, Clarke, and Murray 1977, Murray
1969,Murray and Clarke I980).-The number .. and ~Clarke ~1980, MurraY,Johnson, _and
of Partula "species" is thus reduced to seven Clarke 1982).
(P. taeniata Morch, P. exigua Crampton, P. The geographical ranges of the taxa prior to
suturalis Pfeiffer, P. tohiveana Crampton, P. the introduction of Euglandina are shown in
aurantia Crampton, P. mooreana Hartman, Figure 2 (pages 99 and 100).
II i ...:Z
Extinction of Endemic Species-CLARKE, MURRAY, AND JOHNSON 99
FIGURE 2. The ranges of the different species of Partu/a on Moorea prior to the introduction of Eug/andina rosea:
(A) Partu/a taeniata (N = P. taeniata nuc/eo/a, Sp = P. t. spadicea, St = P. t. strio/ata, Si = P. t. simu/ans , E = P. t.
e/ongata); (B) Partu/a exigua (E) and P. mirabi/is (M); (C) Partu/a suturalis (V = P. suturalis vexi//um, S = P. s.
strigosa, D = P. s. dendroica); (D) Partu/a mooreana (M), P. tohiveana (0), and P. aurantia (A).
Extinction of Endemic Species- CLARKE, M URRAY, AND JOHNSON 101
THE INTRODUCTION OF Achatina AND
Euglandina
The giant African snail, Achatina fulica
Bowdich, is well known as an agricultural pest
(Mead 1961, 1979). It was introduced into
Tahiti (by someone who wished to breed it for
food) in 1967 and spread rapidly to the other
islands in the archipelago. Its numbers increased
in Moorea to such an extent that the
snails invaded human dwellings, and on one
occasion two wheelbarrow-loads of snails
were taken from the walls of a single house (R.
Brosious, pers. comm.). Because Achatina,
unlike Partula , eats living plants, it caused
great damage to crops and gardens. The numbers
of A.fulica apparently reached a peak on
Moorea in 1978, and thereafter declined. The
cause of this decline is unknown (see below),
but the very large numbers of empty unbroken
shells found all over the island suggest
an epidemic disease (or perhap s predation by
land planarian s; see Mead 1979: 70). Living
Achatina are still common on Moorea, and
still cause damage to crops, but the scale of
the problem has greatly diminished.
Euglandina .rosea was introduced into
Tahiti and Moorea in an attempt at the
" biological control" of Achatina fulica.
Euglandina rosea, which is native to Florida
and centralAmerica, is a carnivorous mollusc
that preys upon other land snails. Although it
certainly eats Achatina, there is, as far as we
know, little evidence that it is an effective
agent ofcontrol (Mead 1979). Nevertheless, it
has been widely recommended for this purpose
by departments of agriculture in various
countries. It is still so recommended by the
South Pacific Commission.
Euglandina rosea was introduced into
Moorea, with the approval of the Service de
L'Economie Rurale and the Division de
Recherche Agronomique, at the orange plantation
of M. Nardi in Paopao on 16 March
1977 (J. L. Reboul, pers. comm.). It spread
into the adjoining forests, and by 1980 its
range covered approximately 4 km 2
, very
nearly a third of' the isla-rid. Its rate of spread
between 1980 and 1982 was approximately
1.2 km per year (Figure 3). If the spread continues
at the present rate , Euglandina will
occupy the whole island by 1986 or 1987.
TH E EFFECT OF Euglandina ON Achatina
The decline in the numbers of Achatina
fulica on Moorea since 1978:-1979 cannot
rigorously be ascribed to the effects of
Euglandina rosea. Living Achatina are still to
be found in the territories occupied by Euglandina,
and the decline in the number ofAchatina
has been observed in parts of the island
not yet reached by the carnivore, for example
Aareo Valley and Vaihiiaiia Valley. Furthermore,
a similar decline has occurred on the
island of Huahine, to which E. rosea has not
yet been introduced (Pointier and Blanc 1982).
THE EFFECT OF Euglandina ON Partula
Although the role of Euglandina in controlling
Achatina is doubtful, there is unfortu.nately
no doubt at all about its effects on
Partula . It consumes them with great efficiency.
Four individuals of P. taeniata were
put in a plastic lunch-box with a single E.
rosea. Within 24 hours they had all been
eaten, leaving four empty shells.
During our field studies in 1982·we were
unable, with one exception discussed below,
to find any Partula in the territories now occupied
by Euglandina rosea. Our 1982 surveys
specifically included localities (in Paparoa,
Mouaputa, Faamaariri, and Puutu Valleys)
that had yielded large samples of Partula in
1967 and 1980. Four species (P. aurantia, P.
suturalis, P. tohiveana, and P. taeniata ) seem
to have been entirely eliminated from the
northeast ofthe island. Partula aurantia, which
was restricted to this area (see Figure 2), must
now be considered extinct in the wild state
(the only living examples being tho se kept
alive by James Murray in the laboratory). The
subspecies P. taeniata striolata is also, we believe,
extinct.
The single exception is Partula exigua. This
taxon is restricted to the northeast (see Figure
2), although it is closely related to P. taeniata
and hybridizes withg(l\tlllrraL~!!cl _CJ~[ke
1980).Prior tot he introduction of Euglandina
it tend ed generally to be less common than its
sympatric relatives (P. taeniata , P. suturalis,
and P. aurantia). In 1982 we found a few
scattered individuals of P. exigua or
102 PACIFIC SCIENCE, Volume 38, April 1984
•••
••
•
••
••••••••••••
••
•••
•• •• ••
•••• •
I
t.."
FIGURE3. The spread ofEuglandina rosea on Moorea. The black circle represents the site ofits introduction in 1977.
The vertically hatched area represents its range in 1980, and the ho rizontally hatched area its range in 1982. The black
dotted line represents its expected range in 1984, and the serrated line its expected range in 1986. The star represents the
site ofa seconda ry introduction (in Fa ataai Valley) the success of which is unknown. Ifit proves successful, the spread
of Euglandina is likely to be faster than shown in this figure .
taeniatalexigua hybrids surviving where the
other Partula were extinct (in Faamaariri and
Mouaputa Valleys). We are not yet able to
give a reason for the "escape" of some P.
exigua, or to tell whether the phenomenon is
transient or lasting.
An incidental consequence of the spread of
Euglandina is the raising of Partula tohiveana
to the status of a good biological species.
Until 1980 P. tohiveana and P. suturalis
- formed a ring-species, the zone of.intergradation
being to the east of Mt. Mouaputa
(Murray and Clarke 1980). Populations from
this zone have now been eliminated, and the
remaining populations of tohiveana are sympatrie
with, and distinct from , suturalis.
The rate at which Euglandina is spreading
(Figure 3), and the known ranges of the
Partula taxa (Figure 2), allow us to make clear
predictions about the years in which the taxa
are expected to become extinct in the wild.
These are given in Table 1. The majority are
expected to die out by 1986.
THE THREAT TO Partula ON OTHER ISLANDS
H. E. Crampton, in addition to his work
on Moorea, wrote two further evolutionary
monographs, one on the Partula of Tahiti
(1916),the other on the Partula of Guam and
Saipan (1925). These snails, too, are under
.. m:z:::z::::z::: . , ., ! , :.I...!J a; 1,P. 4;
Extinction of Endemic Species- CLARKE, MURRAY, AND JOHNSON 103
ACKNOWL EDGMENTS
REMEDIAL MEASURES
TABLE I
PREDICTED Y EARS OF EXTINCTION OF Partula FROM
M OOREA
1984
1985
1985
1984
1986
1986-1 987
PREDICTED YEAR
OF EXTINCTION
already extinct
1984
1986
1986
1986-1987
uncert ain (see text)
already extinct
1983
Partula taeniata striolata
Partula taeniata spadicea
Partula taeniata elongata
Partula taeniata simulans
Partula taeniata nucleola
Partula exigua
Partula aurantia
Partula tohiveana olympia
(P. olympia Crampton)
Partula tohiveana tohiveana
Partula mirabilis
Partula mooreana
Partula suturalis dendroica
(P. dendroica Crampton)
Partula suturalis strigosa
Partula suturalis vexi/lum
TAXON
We see no hope of stopping the spread of
Euglandina on the islands where it has already
become established. There is, however, a very
good case for discouraging new introductions,
whether by governmental programs, by
private enterpriseon the part oflocal farmers ,
or by accident.
In an attempt to preserve the Moorean taxa
of Partula we have established breeding colonies
in our laboratories. Other colonies have
been set up by the Jersey Wildlife Preservation
Trust and by the Zoological Society of
London. However, even if these colonies can
successfully be maintained, a valuable genetic
resource will have been lost.
We believe that our observations on the
effects of Euglandina may be worth the attention
of the workers and governmental agencies
concerned in attempts to control
Achatina and other pest species. They show
that programs of "biological control" may
have very dangerous consequences to local
faunas.
We are very grateful to Bernard Salvat,
Rene Galzin, and Gilbert Vergonzanne for
TH E THREAT TO OTHER GENERA OF LAND
SNAILS
threat. In Tahiti Euglandina rosea was established
during 1974 and now occupies the
whole of the Temarua Valley, above the village
of Papara, and the entire plateau of
Taravao, above the village of Afaahiti. In
these areas the native Partula appear to have
been eliminated (Pointier and Blanc 1982).
Because Tahiti, with a diameter of about
30 km, is a larger island than Moorea, some of
the Tahitian Partula may survive longer than
the Moorean ones, perhaps until the 1990s.
The situation is probably worse in Guam and
Saipan. Not only is Euglandina rosea well
established on both islands, but two other
carnivorous snails (Gonaxis quadrilateralis
(Preston) and Gonaxis kib weziensis (E. A.
Smith» also have been introduced (Mead
1979).
In view of the rapid spread of Achatina
among the Society Islands, both by accidental
and by intentional transport , it seems very
probable that Euglandina will reach many
other islands within the next few years.
We have not studied the effect of Euglandina
on the two Moorean species of
Samoana (Samoana diaphana (Kondo) =
Partula diaphana Crampton and Cooke, and
Samoana attenuata (Pease) = Partula solitaria
Crampton), but if they prove to be as susceptible
to Euglandina as the other Partulidae we
can expect them to be eliminated from the
island before 1987. The same is true of the
arboreal snail Trochomorpha pallens Pease,
which seems now to be absent from the territories
occupied by Euglandina .
The introduction of Euglandina and other
carnivores has been implicated in the extinction
of many endemic snails in the Hawaiian
islands (van der Schalie 1969, Hadfield and
Mountain 1980, Kondo, pers. comm.).
Euglandina has been successfully introduced
intoMauritius, the Seychelles, La Reunion,
the New Hebrides, and New Caledonia (Mead
1979). The number of endemic speciesthat are
endangered or already extinct as a result of
the introductions must now be well over a
hundred.
104
their hospitality, and much practical help, at
the Centre de l'Environnement, Moorea; to
Jean-Pierre Pointier, Charles Blanc, and
Yoshio Kondo for allowing us to mention
their unpublished work; and to the Science
and Engineering Research Council for financial
support. We also thank the Fauna and
Flora Preservation Society, and the Onaway
Trust, for financial help in setting up breeding
colonies of Partula.
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