Cayot, Linda J.

Olmedo, Janeth

English

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April 1994 NOTICIAS DE GALAPAGOS
INTRODUCED GECKOS IN THE TOWNS OF SANTA CRUZ' SAN
CRISTOBAL AND ISABELA
By: Janeth Olmedo and Linda J. CaYot
INTRODUCTION
Introduced organisms often negatively affect is-
land ecosystems (MacDonald et al. 1989, Loope and
Mueller-Dombois 1989). While most examples of
these negative effects involve organisms other than
reptiles, there are cases where introduced reptiles,
such as the brown tree snake(Boigairregularis),have
had disastrous effects on native fauna (Marshall 1985).
The impact of introduced organisms in Galápagos is
well documented (Hamann 1984, Hoeck 1984).
However, little is known about the impact of the in-
troduced reptiles.
The only introduced reptiles that have established
reproductive populations in Galápagos are in the fam-
ily Gekkonidae. The status of introduced gecko
species was reviewed in 19 89 Qloogmoed 1 989). The
large introduced gecko in Puerto Ayora, Santa Cruz,
Phytlodacrylus reissi,was seen frrstin the mid 1970s
and was probably brought to the Islands via the reg-
ular cargo boat service from Guayaquil.
LepidodacryIus lugubris was also introduced to San-
ta Cruz (Wright 1983a, 1983b). Gonatodes
caudiscutatus, the third introduced species of gecko
in Galápagos, is found only on S an Cristóbal and was
fkst recorded there in 1 892 (Van Denburgh 19 12). ln
addition, Phyllodacrylus leei, a species endemic to
San Cristóbal, was reported in Puerto Villamil on
Isabela (Wood 1939), but no further observations of
this species on Isabela have been made. Hoogmoed
(1939) recommended regular monitoring of the in-
troduced gecko populations and that a decision be
made as soon as possible whether the eradication of
the introduced geckos is of high priority.
In Galápagos there are six endemic species of
geckos, all of the genas PhyllodacryIus. All are rel-
atively small and are generally restricted to the Arid
Zone. Of the introduced species, only P. r¿issi has
habitat requirements similar to the endemic species,
restricted to arid coastal areas. Gonatodes caudiscu-
tatus requires relatively wet areas; it is found in the
wet highlands of San Cristóbal and in artifrcially wet
gardens in the coastal town of Puerto Baquerizo
Moreno (Hoogmoed 1989). Lepidodacrylus lugu-
bris is generally associated with humans throughout
the coastal areas of the southern and central Pacific.
In Galápagos it appears to be restricted to coastal
areas. All of the endemic species lay only one egg,
except for P. darwini, which can lay 1-2 eggs, while
all of the introduced species lay two eggs. In addi-
tion, Lepidodøctylus lugubris is parthenogenic.
ln1992-93,a study of the introduced andendemic
species of geckos in the populated areas of the five
inhabited islands was completed. The primary ob-
jective was todetermine the distribution of thevarious
species and the impact and potential threat of the
introduced species on the endemic species.
METHODS
This study was carried out on Santa Cruz, San
Cristóbal, Isabela,FloreanaandBaltra. Lowlanda¡eas
with human habitations were monitored on all is-
lands, while highland areas were monitored only on
the first three. Monitoring was done in both the hot
and garua seasons (Table 1). Each inhabited areawas
divided into sectors. Amonitoring period consisted
of observations in one sector per night (15 houses
randomly selected per sector), on consecutive nights
until all sectoß had been completed. In addition, in
each of the three main ports (Puerto Ayora, Puerto
Baquerizo Moreno and Puerto Villamil), eight 50-m
transects into the natural habitat surrounding the
developed areas wete checked (two transects in each
NOTICIAS DE GALÁPAGOS No.53
Table 1. Dates of sampling periods in each of the five populated islands.
SANTA SAN
SEASON MONTTI CRUZ CRISTÓBAL ISABELA BALTRA FLOREANA
HOT Mayl92
June/92
GARUA July/92
Aug/92
Sept/92
Oct/92
Nov/92
X
X
X
GARUA
DecD2
Janl93
Feb/93
Ma¡chr93
AprilÆ3
May/93
June/93
July/93
Aug/93
Sepl93
Octl93
X
X
X
X
X
X
of the cardinal directions).
When possible, geckos were captured, measured
and their sex and age group determined. Total num-
ber of observations include both captured and
non-captured animals.
RESULTS
Gecko disribution on rhe inhabited islands is as
follow s : S anta Cruz -- P hy llo dac ry lus g al ap a g o e ns is(endemic), P hyllodacrylus reissi (introduced), Lepi-
dodacryIus lugubris (inroduced); San Cristóbal --
P hyllo dac tylus darwi ni (endemic), p hy llo dac ry lus
leei (endemic), Gonatodes caudiscuta¡ts (int¡o-
duced), Lepido døcry lus lugubris (introduced); Isa-
bela -- Phyllodactylus galapagoensís (endemic),
Lep ido dac rylus lugubris (introduced); Floreana --
P þ llodactylus bauri (endemic); Baltra 
- 
p hyllodac -
ry lus g alap ag o e ns is (endemic).
The introduced species Lepidodactylus lugubris
was reporred fo¡ the first time on both San Cristóbal
and Isabela. Both Floreana and Baltra a¡e apparentþ
still free of introduced geckos.
P. darwini, one of the endemic species on San
Cristóbal, andP. reissi,one of the introduced species
on Santa Cruz, ale the largest ofthe geckos studied
(Table 2).
In Sanø Cruz, introduced geckos were foundonly
April 1994 NOTICIAS DE GALÁPAGOS
in PuertoAyora, not in the highlands. In the six sam-
plingperiods, the totalnumberof observations of the
endemic species (n = 2950) was more than three times
greater than the total number of observations of the
two introduced geckos (P. re i s s, n = 657 ; L. lu gubri s,
n = 193). P. reissi was observed in nearly all sectors
of town, but, based on numbers of observations, it is
dominant only in the three sectors surrounding the
dock (Fig. I). Lepidodacrylus lugubrís was only
observed in four coastal sectors, generally in a¡eas
with mangroves. Only one observation of an intro-
duced gecko (P. reissi) was made in the natural habitat
transects surrounding PuertoAyora, while there were
34 observations of the endemic species. The one
obsewation of P. reissi was in a transect adjacent to
theNinfas neighborhood, which had the secondhigh-
est number of observations of that species.
In San Cristóbal, the two endemic species were
found in all sectors of Puerto B aquerizo Moreno (Fi g.
2). Both of the introduced species, G. caudiscutatus
andL.lugubri.r, wete present in few sectors, genelal-
ly close to the town dock. Both appear to be restricted
to fairly humid habitats. Only the endemic species,
P. leei, was observed in the natural habitat transects
(n = 4). G. caudiscutatus was much more abundant
in the highlands andwas found notonly in the village
El Progreso (Fig. 2), but also in the farmlands (5
observations in a sample of two houses and 29 in the
farm area surrounding the houses) and in the Galápa-
gos National Park (GNP) (1 observation).
In Isabela, the endemic species was observed in
all sectors of Puerto Villamil, while the introduced
species, Lepídodacrylus lugubris, was observed in
only two sectors (Fig. 3). Only the endemic species
was observed in the natural habitat transects (n = 4).
Table 2. Snout-vent length (SVL, mean and standard deviation) of gecko species in the populated is-
lands.
MALE FEMALE
SPECIES
Endemic
P. galapagoensis
P. bauri
P.leei
P. darwiní
Introduced
P. reissi
L.lugubris
G. caudiscutatus
ISLAND N SVL
Santa Cruz
Isabela
Baltra
Floreana
San Cristóbal
San Cristóbal
Santa Cruz
Santa Cruz
Isabela
San Cristóbal
San Cristóbal
N SVL
41.4 + 4.7
43.1+ 4.4
43.5 + 3.5
46.6 + 5.8
41.9 + 3.2
65.6 + 9.0
103 62.2 + 14.3
2 40.1+ 4_.1
7 40.1 + 2.1
700 40.9 + 5.5
130 42.4 + 5.4
19 44.7 + 4.4
38 43.4 + 5.8
43 42.0 + 3.8
39 58.7 + 10.7
139 56.3 + 13.8
53 39.4 + 4.1
6 41.2 + 2.5
21 41.5 + 2.5
24 38.4 + 3.2
611
89
t7
27
39
22
10 NOTICIAS DE GALÁPAGOS No.53
$ enfløaacrytus gatapagoensis
@ enttbaactyfus reissi
@ teniaoAacgtus lugubris
Figure 1' Total number o{^obryrv4¡_o¡¡-gf gecko species in the 23 sectors of Puerto Ayora, Santa Cruz; includes data from six
sampling periods (May 1992 - April 1993).
$gufç ?. Total number of observations.of gecko.species in the 14 sectors of Puerto Baquerizo Moreno and in El hogreso, SanCristóbal; includes data from two samplingþeriods (August 1992 utd.March 1t93).
.:::¡:::r El PfogfeSO
.:ii .ft r
-f- i!)
$ enlrca.ctytus teei
$¡ enytøa"ctytus darwini
@ tepiaoaactytus lugubr¡s
@ Gon^rod.s caudiscutatus
April 1994 NOTICIAS DE GALAPAGOS 11
$ e nrrcaacltus gatapagoensis
@ Lepidodactytus lugubris
Figure 3. Total number of obse¡vations of gecko species in the 10 sectors of Puerto Villamil, Isabela; includes data from two
sampling periods (October 1992 and June 993).
DISCUSSION
In summary, results from this study indicate that
introduced geckos have resident populations on the
three islands with greater human populations (Santa
Cruz, San Cristóbal and Isabela), but not on Floreana
or Baltra. The dispersion of the introduced species
appears to be from the dock ofeach port, where cargo
arrives from ships, presumably carrying the inno-
duced organisms. Since the distribution of each
species depends not only on the point of a¡rival, but
also on their preferred habitat, the potential threat of
the introduced geckos to the endemic geckos depends
primarily on the preferred habiøt of each species.
The dispersi on of P hyllodactylus reissi in Puerto
Ayora appears to be from the dock area towards the
center of the town. Where it exists in greater num-
bers, it appears to have displaced the endemic species.
In only a few cases are both species seen together on
the same wall. While the distribution of P. reissi
remains limited to the town, it does not present a
major threat to the endemic species in the GNP.
However, it could become a threat if it spreads into
the GNP (Hoogmoed 1989). A campaign to reduce
numbers or eliminate P. r¿issi in Puerto Ayora, espe-
cially in the areas close to the GNP boundary, would
be warranted, possibly enlisting the aid of high school
students in coordination with educational programs
on the problems of introduced species.
Lepidodacrylus lugubris is apparently restricted
to the coastal zone where there is adequate humidity,
often areas with mangroves. It therefore does not
present a major threat to the endemic geckos, which
are restricted to the Arid Zone. However, it is more
likely to successfully disperse throughout the Archi
pelago than the other species due to its disribution
along the coast and the fact that it is parthenogenic.
Of the three species, G. c audiscutatuswas theonly
one found outside the inhabited areas. Individuals
were observed primarily in the highlands (in El Pro-
greso, in farmlands and in the GNP). The generally
humid habitat of this species does not support the
endemic geckos, which occur only in xeric habitats.
Therefore, the direct impact of G. caudiscutatus on
the endemic species of gecko in San Cristóbal is
minimal.
T2 NOTICIAS DE GALÁPAGOS No.53
Unlike the impact of many other organisms intro-
duced to the Galápagos Islands (including plants,
insects, mammals, etc.), the introduced geckos do not
present a serious threat to the endemic species. We
consider that conservation efforts, which depend on
limited funds and personnel, should be directed at the
more aggressive and dangerous introduced species
rather than the geckos. However, periodic monitor-
ing of all introduced species and low-cost control
efforts of P. reissi in PuertoAyora should be ca¡ried
out.
ACKNOWLEDGMENTS
Thank you to Heidi Snell for the graphics.
LITERATURE CITED
Hamann, O. 1984. Changes and th¡eats ro the veg-
etation. in Perty, R., ed. Galápagos. Pergamon
Press, Oxford. Pp. 115-131.
Hoeck, H.N. 1984. Introduced fauna. in Perry, R.,
ed. Galápagos. Pergamon Press, Oxford. h.
233-245.
Hoogmoed, M.S. 1989. Introduced geckos in Puerro
Ayora, Santa Cruz, with remarks on other areas.
Noticias de Galápagos 47:12-16.
Loope, L.L. and D. Mueller-Dombois. 1989. Char-
acteristics of invaded islands, with special reference
to Hawaii. in Drake, J.4., H.A. Mooney, F. di
Castri, R.H. Groves, F.J. Kruger, M. Rejmnek and
M. Williamson, eds. Biological invasions: a glo-
bal perspective. John Wiley & Sons, Chichester.
Pp.257-280.
MacDonald, I.A.W., L.L. Loope, M.B. Usher and O.
Hamann. 1989. V/ildlife conservation and the
invasion ofnature reserves by introduced species:
a global perspective. in Drake,J.A., H.A. Moon-
ey, F. di Castri, R.H. Groves, F.J. Kruger, M.
Rejmnek and M. Williamson, eds. Biological in-
vasions: a global perspective. John Wiley & Sons,
Chichester. Pp. 215-255.
Ma¡shall, J.T. 1985. Guam: a problem in avian con-
servation. Wilson Bulletin 97 :259-262.
Van Denburgh,J. 1912. Expedition of the Califomia
Academy of Sciences to the Galápagos Islands,
1905-06. VI. The geckos of the GalápagosArchi-
pelago. Proceedings of the Califomia Academy
of Sciences, Fourth Series, l:405-430.
Wood, G.C. 1939. Results of the Pinchot Sourh Sea
Expedition. III. Galápagos repriles. Notulae
Naturae 75:l-4.
Wright, J.W. 1 983a (revised May 1984). Reptiles of
the Galápagos Archipelago. Unpublished report.
1p.
Wright, J.W. 1983b (revised 1984, 1988). Reptiles
of the Galápagos Archipelago. Unpublished re-
port. 2 pp.
Janeth Olmedo and Linda J. Cayot, Charles Dar-
win Research Station,Isla Santa Cruz, Galápagos,
Ecuador.
r-


Introduced geckos in the towns of Santa Cruz, San Cristóbal and Isabela

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Introduced geckos in the towns of Santa Cruz, San Cristóbal and Isabela

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