Roque, Lázaro

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April 1998 NOTICIAS DE GALÁP AGOS 9
THE MONARCH BUTTERFLY IN THE GALÁPAGOS ISLANDS:
IS IT A NATIVE OR AN INTRODUCED SPECIES?
By: Lázaro Roque
When I returned to the water party I saw two
monarch butterflies flying slowly about, and we
stopped work for a moment, but lacking a net, found
it impossible to capture them. There was not the
remotest chance of being mistaken in the species,
and therefore Oanais (sic) p/exippus (or Oanais
archippllSas Iknew it when a boy) is definitely added
to the fauna of the Galápagos Archipelago. On
several islands I had seen a milkweed in blossom,
so this wide-ranging butterfly should ha ve no dif-
ficulty in establishing itself.
William Beebe, 1924, Ga/apagas: War/d'sEnd
One of the favorite topics in the study of insular biol-
ogy is the analysis or speculation about the arrival and
establishment of a species on oceanic islands. The
Galápagos Islands, located 1000 km off the coast of Ecua-
dor, are a singular place for such biogeographic and
~
Figure 1. Adult D. plexipplls at rest, Floreana, April1996 (photo
by Lázaro Roque).
evolutionary studies. Determining if species of insects
were introduced by humans or if they have naturally
colonized the islands is not always an easy matter. For the
monarch butterfly (Danalls plexipplls), the answer to that
question remains uncertain.
Hickin (1979) mentioned that it may have been intro-
duced to San Cristóbal Island as a result of the frequent
visits of commercial ships to the island. However, Peck
(1991) wrote that the only mechanism for butterflies to
arrive at the Galápagos Islands was by air, flying actively
or passively. The only report of this species prior to this
publication was that of Beebe (1923).
Zimmerman (1948) recognized four mechanisms by
which insects could arrive at an oceanic island:
a) transported by other animals,
b) on natural rafts,
c) transported intentionally or accidentally by
human beings, and
Figure 2. Caterpillar 5thinstar in A. cllmssavica, Floreana, April
1996 (photo by Lázaro Roque).
10 NOTICIAS DE GALÁP AGOS No. 59
d) through the air, flying actively or passively.
Only the last three modes of transport are likely to
apply to diurnal butterflies.
1. Rafts: The transport of insects on natural rafts has
been documented (Palmer 1944, Heatwole and Levins
1972, Peck 1994). This mechanism is less probable for
adult butterflies. Nevertheless, it is possible that rafts,
driven by either the Humboldt Current (during the dry
sea son) or the Panama Flow (during the rainy sea son,
especially during a strong El Niño year) could arrive with
eggs,larvae, or pupae. It should be emphasized that the
probability of successful establishment of the immature
stages transported on rafts is low due to the fact that at
least one mal e and one female must survive and find a
milkweed to ensure the establishment of the species. Peck
and Kukalová-Peck (1990) pointed out that another factor
affecting the establishment of native insects after raft trans-
port is the predation pressure of native lizards and birds.
The intense activity of these insectivorous predators has
been observed along many coasts of the islands.
2. Human Beings: There are no data on the intentional
in trod uction oflepidopterans to the Archi pelago, although
the importation of plants could playa significant role in
the indirect introduction of insects (Miller 1994). Human
settlements in Galápagos are relatively recent. The first
inhabitants settled on Floreana and San Cristóbal during
the last century, bringing many plants, mainly fruits and
vegetables, but also ornamental plants (Mauchamp 1997).
Ase/epias curassavicaL., the main milkweed host plant
of D. plexippus in Galápagos, is an introduced plant and
grows mainly in the agricultural zones of Floreana, Santa
Cruz, and San Cristóbal (Lawesson et al. 1987). It was
collected for the first time by the year-Iong expedition of
the California Academy of Sciences in 1905-06 (Stewart
1911). However, the entomologist of that expedition, F. X.
Williams, a very capable lepidopterist, neither collected
nor observed the butterfly (Williams 1911). Based on this,
it is possible to suggest that the species was not intro-
duced before this date.
3. Flying: The long -distance dispersal abili ties of man y
lepidopterans are well known (Guppy 1925, Beebe 1949,
Ferguson et al. 1991, Smith 1992). D. plexippus is famous
as a long-distance migrant, because it performs spectacu-
lar annual migrations in North and Central America and
on occasions over the Pacific (Carlquist 1981).
Zwaluwenberg (1942) verified repetitive colonization by
the species on remo te Canton Island, in the central Pacific,
and at the same time detected the simultaneous establish-
ment of the host plants. It is probable that Galápagos has
had many such arrivals and failed attempts to colonize
where there are no A. curassavica plants. Peck (1994) dem-
onstrated that the winds in a strong El Niño year probably
crea te favorable circumstances for the transport of insects
between islands and from tropical America to Galápagos.
During the past two years (1995-96), 1have collected
D. plexippus on San Cristóbal, Santa Cruz, and Floreana.
1 have found eggs and early instar larvae on the plants
Ase/epias curassavica L. and Sarcostemma angustissima R.
W. Holm (Asclepiadaceae). The latter species is wide-
spread throughout Galápagos. 1have the impression that
on islands where both milkweed plants occur, when the
abundance of A. curassavica decreases as a result of herbi-
vore pressure, the frequency of ovapositions on S.
angustissima increases. Larval development, however,
appears to be incomplete on this second milkweed spe-
cies and may be why the monarch butterfly is only found
on the islands where A. curassavica grows.
Based on the current distribution and well-established
dispersal potential of this species, together with dates of
discovery ofbutterflies and their host plant, it seems most
reasonable to assume that D. plexippus arrived in the Ar-
chipelago between 1906 and 1923 through natural
dispersal mechanisms, after humans had introduced the
milkweed host planto
ACKNOWLEDGMENTS
1am grateful to the director of the Galápagos N ational
Park Service, Eliecer Cruz, and the director of the Charles
Darwin Research Station, Chantal Blanton, for permis-
sion to sample and for support in this research.
1thank Stewart B. Peck for his encouragement to write
this paper and for useful suggestions in the manuscript.
Bernard Landry, William Eberhard, Priscilla Martínez,
Rita Spadafora, Cruz Márquez, Hernán Vargas, Chantal
Blanton, Alan Tye, Howard L. Snell, and Heidi M. Snell
are thanked for making constructive comments on this
paper. Valentina Cruz was an excellent field assistant for
this study. TAME airlines of Ecuador provided air travel
at a reduced rateo
LITERA TURE CITED
Beebe, W. 1923. Notes on Galapagos lepidoptera. Zoologica
5(3): 51-59.
Beebe, W. 1949. Insect migration at Rancho Grande in North-
Central Venezuela. General account. Zoologica 34: 107-11O.
Carlquist, S. 1981. Chance dispersa1. Am. Scientist 69: 509-516.
Ferguson, D. C, D. J. Hilburn, and B. Wright. 1991. The lepi-
doptera of Bermuda: their food plants, biogeography and
means of dispersa1. Mem. Ent. SocoCanada. 158 pp.
Guppy, H. B. 1925. Dispersal of butterflies and other insects.
Nature 116: 543.
Heatwole, H. and R. Levins. 1972. Biogeography of the Puerto
Rican bank: flotsam transport of terrestrial animals. Ecol-
ogy 53: 112-117.
Hickin, N. 1979. Animallífe of the Galapagos. Ferendune
Books, Faringdon, England. 236 pp.
Lawesson, J. E., H. Adsersen, and P. Bentley. 1987. An updated
and annotated check list of the vascular plants of the
Galapagos Islands. Reports fram the Bot. Inst., Univ. of
Aarhus 16: 1-74.
Mauchamp, A. 1997. Threats from alíen plants species in the
Galápagos Islands. Conservation Biology 11(1): 260-263.
Miller, 5. E. 1994. Dispersal of plant pests into the Virgin ls-
lands. Florida Entomologist 77(4): 520-521.
Palmer, E. 1944. Die anemohydrachore austbreitung der insekten
als zoogeographischer faktor. Ann. Zoo1. Soco Zoo1. Bot.
Fenn. Vanano 10: 1-262.
April1998 NOTICIAS DE GALÁP AGOS 11
Peck, S. B. 1991. The Galapagos Archipelago, Ecuador: with an
emphasis on terrestrial invertebrates, especially insects; and
an outline for research. In E. C. Dudley, ed., The Unity of
Evolutionary Biology, Proc. 4th Internl. Congo Systematics
& Evol. Biol., pp. 319-336, Dioscoroides Press, Portland, OR.
Peck, S. B. 1994. Sea-surface (pleuston) transport of insects
between islands in the Galápagos Archipelago, Ecuador.
Ann. Ent. SocoAm. 87(5): 576-582.
Peck, S. B. and J. Kukalová-Peck. 1990. Origin and biogeogra-
phy of the beetles (Coleoptera) of the Galápagos Archipelago,
Ecuador. Can. J. Zool. 68: 1617-1638.
Smith, N. G. 1992. Reproductive behaviour and ecology of Uranía
(Lepidoptera: Uraniidae) moths and of their larval food
plants, Omphalea spp. (Euphorbiaceae). In D. Quintero and
A. Aiello, eds., Insects of Panama and Mesoamerica, selected
studies, pp. 556-593, Oxford Univ. Press.
Stewart, A. 1911. Expedition of the California Academy of
Sciences to the Galapagos Islands, 1905-1906. II. A botanical
survey of the Galapagos Islands. Prac. Cal. Acad. Sci., 4th
Ser. 1: 7-288.
Williams, F. X. 1911. Expedition of the California Academy of
Sciences to the Galapagos Islands, 1905-1906. III. The butter-
flies and hawk-moths of the Galapagos Islands. Proc. Calif.
Acad. Sci., 4th Ser. 1: 289-322.
Zimmerman, E. C. 1948. The insects of Hawai'i. 1.Introduction.
Univ. Press of Hawai'i, Honolulu. 206 pp.
Zwaluwenberg, R. H. van. 1942. Notes on the temporary estab-
lishment of insect and plant species on Canton Island.
Hawaiian Planter's Record 46: 49-52.
Lázaro Roque, Charles Oarwin Research Station,
Galápagos, Ecuador (e-mail: lazaro@fcdarwin.org.ec).
ANTS (HYMENOPTERA, FORMICIDAE) OF FLOREANA:
LOST PARADISE?
By: Boris Pezzatti, Trimurti Irzan, and Daniel Cherix
INTROOUCTION
Ecological impacts of introduced mammals and plants
on the endemic fauna and flora of Galápagos is an impor-
tant problem that has been relatively well documented
(e.g., Hoeck 1984, Hamann 1991, 1994). However, little is
known about the impact of introduced arthropods (Baert
1994, Meier 1994). Especially among ants, so-called
"tramp" species have been readily transported by hu-
manso Due to their biological characteristics, these "tramp"
species become rapidly established and can spread out
easily. Although small in size, ants are among the most
widespread and destructive invading species. Introduced
into a new area, they become real pests and can either
displace or elimina te native ant species or other
arthropods, like the imported fire ants Solenopsis invicta
Buren in the United States (see, e.g., Vinson 1994). One of
the most recent introductions, with far-reaching conse-
quences for the Galápagos ecosystem, is the little red fire
ant, Wasmannia auropunctata (Roger) (Lubin 1984).
In the late 19th and early 20th centuries, several papers
on ants were published based on material collected dur-
ing early expeditions to the Galápagos Islands (Smith 1877,
Emery 1893, Wheeler, 1919, 1924, 1933, Stitz 1932). No
further studies on ants were published untiI1972, when
problems caused by the introduction of W. auropunctata
arose (Silberglied 1972). Although a number of studies
have been conducted, particularly on W.auropunctata and
its control (Clarket al. 1982, Lubin 1984, 1985, Meier 1994,
Ulloa-Chacón and Cherix 1990, 1994), the resultingknowl-
edge is still considered fragmentary (Brandao and Paiva
1994).
The aim of this study was to determine patterns of
distribution of the ant fauna on the island of Floreana,
with special attention to introduced ants. For this pur-
pose, species richness, abundance, and frequency of the
ant fauna were studied (Pezzatti, Irzan, and Cherix, in
prep.). In addition, different collecting methods were
compared as a first step in the development of standard-
ized methods for further investigation of ants on the
Galápagos Islands (Irzan and Pezzatti 1997).
Floreana Island was selected for this research beca use
both old (Wheeler 1919, 1924, 1933) and more recent data
(Lubin 1984) on ant fauna were available. Moreover, the
history of Floreana and its present situation made it an
interesting study site. The early colonization and intro-
duction of plants and animals ha ve had an important
influence on the native fauna and flora, and we supposed
that the ant fauna would have been similarly affected.
MATERIAL ANO METHOOS
Study Site
The vegetation zones, originally described by Wiggins
and Porter (1971) are partly represented on Floreana. The
littoral zone and the transition zone are very reduced on
the lee side of the island, i.e., on the northern and western
slope (DI. Alan Tye [Head, Department of Plants and ln-
vertebrates of the Charles Darwin Research Station
(CDRS»),IvánAldaz [Botanist, CDRS] , pers. comm.;pers.
obs.).
In the humid highlands ofFloreana, two different "sub-
zones" of the Scalesia zone can be distinguished: one area


The monarch butterfly in the Galápagos Islands : is it a native or an introduced species?

http://aquaticcommons.org/7442/1/NG_59_1998_Roque_Monarch_Butterfly.pdf

The monarch butterfly in the Galápagos Islands : is it a native or an introduced species?

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