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Abstract

the spiders of rapa nui have not been assessed in over two decades. During this time, additional nonnative alien species introductions would be expected due to increased tourism visitation and the steady influx of commercial goods imported from mainland Chile. Prior to our work, only one endemic species (Tetragnatha paschae Berland, 1924) was known to occur on the island. We conducted multiple research trips (from 2008–2012) and examined 15 different study sites on rapa nui to search for both this species and other endemic ground-dwelling arthropod species including spiders. Tetragnatha paschae was not detected during our survey. We suggest this spider is probably extinct. our sampling yielded 26 unique spider morphospecies (representing 15 families and at least 20 genera). Based on our research and previous work, we complied a list of 47 morphospecies known to rapa nui – including six new island records. nearly half of these alien morphospecies (n = 23) have cosmopolitan or pantropical distributions. importantly, we detected one potentially endemic and possibly undescribed spider, Tetragnatha sp., which is probably restricted to the native vegetation within one crater lake. the areas with highest spider diversity are likely due to high habitat heterogeneity. We also provide recommendations to expand the search for endemic spider species on rapa nui.
NUMBER 120, 17 pages 25 May 2017
BISHOP MUSEUM PRESS
HONOLULU
BISHOP MUSEUM
OCCASIONAL PAPERS
THE SPIDERS OF RAPA NUI
(EASTER ISLAND) REVISITED
DARKO D. COTORAS, J. JUDSON WYNNE,
LUIS FLORES-PRADO & CRISTIAN VILLAGRA
Cover image: The potentially endemic and undescribed Tetragnatha sp., believed restricted to the totora reeds lin-
ing the shores of Rano Raraku crater lake. Photo: Darko Cortoras.
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BERNICE PAUAHI BISHOP MUSEUM
The State Museum of Natural and Cultural History
1525 Bernice Street
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RESEARCH
PUBLICATIONS OF
BISHOP MUSEUM
The Spiders of Rapa Nui (Easter Island) Revisited
DARKO D. COTORAS1,2
Department of Integrative Biology, University of California, 3060 Valley Life Sciences Building,
Berkeley, California 94720-3140, USA; darkocotoras@gmail.com
J. JUDSON WYNNE2
Department of Biological Sciences, Merriam-Powell Center for Environmental Research, Northern
Arizona University, Flagstaff Arizona 86011, USA; email: jut.wynne@nau.edu
LUIS FLORES-PRADO and CRISTIAN VILLAGRA
Instituto de Entomología, Universidad Metropolitana de Ciencias de la Educación, Santiago, Chile
Abstract. The spiders of Rapa Nui have not been assessed in over two decades. During
this time, additional nonnative alien species introductions would be expected due to
increased tourism visitation and the steady influx of commercial goods imported from
mainland Chile. Prior to our work, only one endemic species (Tetragnatha paschae
Berland, 1924) was known to occur on the island. We conducted multiple research trips
(from 2008–2012) and examined 15 different study sites on Rapa Nui to search for both
this species and other endemic ground-dwelling arthropod species including spiders.
Tetragnatha paschae was not detected during our survey. We suggest this spider is prob-
ably extinct. Our sampling yielded 26 unique spider morphospecies (representing 15
families and at least 20 genera). Based on our research and previous work, we complied
a list of 47 morphospecies known to Rapa Nui – including six new island records. Nearly
half of these alien morphospecies (n = 23) have cosmopolitan or pantropical distribu-
tions. Importantly, we detected one potentially endemic and possibly undescribed spider,
Tetragnatha sp., which is probably restricted to the native vegetation within one crater
lake. The areas with highest spider diversity are likely due to high habitat heterogeneity.
We also provide recommendations to expand the search for endemic spider species on
Rapa Nui.
INTRODUCTION
Rapa Nui (or Easter Island) underwent a catastrophic ecological shift (Wynne et al. 2014)
between Polynesian colonization (800–1200 CE; Martinsson-Wallin & Crockford 2001;
Hunt & Lipo 2006; Shepardson et al. 2008; Wilmshurst et al. 2011) and European contact
(1722; McCall 1990). The palm-dominated shrubland blanketing most of the island ulti-
mately shifted to a grassland system. Geographic isolation, small island size, low topograph-
ic relief (Rolett & Diamond 2004), fire-intolerance (Mann et al. 2008) and limited coloniza-
tion events of biota from South America and other Polynesian islands hastened this dramatic
change. By the mid-nineteenth century, most of the island was converted to a century-long
sheep-grazing operation (Fischer 2005), which exacerbated environmental degradation and
biotic homogenization. In aggregate, these factors resulted in the loss of most stands of
Spiders of Rapa Nui (Easter Island) Revisted. Cotoras et al. Bishop
Museum Occasional Papers 120: 1–17 (2017)
Published online: 25 May 2017 ISSN (online): 2376-3191
1. Current affiliation: Department of Entomology / Center for Comparative Genomics, California Academy of
Sciences, 55 Music Concourse Drive, San Francisco, CA 94118, USA; Department of Ecology & Evolutionary
Biology, University of California, 1156 High St, Santa Cruz, CA 95064, USA.
2. Shared senior authorship.
native vegetation and the extinction of all known land vertebrates (Wynne et al. 2014).
Today, the terrestrial ecosystems of Rapa Nui is characterized by a preponderance of alien
plant and vertebrate species.
The island arthropod community has been equally transformed. Of the nearly 400
arthropod species cataloged, only 31 species (~8%) are endemic or indigenous (Wynne et
al. 2014); the remaining were intentionally or accidentally introduced (Wynne, unpub-
lished data; CONAMA 2008). Ten of these species (one psocopteran, Mockford & Wynne
2013; seven collembolans, Jordana & Baquero 2008; Bernard et al. 2015; and, two
isopods, Taiti & Wynne 2015) are endemic and believed restricted to caves (Wynne et al.
2014). Most of the remaining 21 endemic species have not been observed since their ini-
tial descriptions, and are either probably extinct or occur in such low numbers as to have
evaded detection.
Rapa Nui spiders have not been examined in nearly two decades. The first document-
ed arthropod study identified three spider morphospecies (Fuentes 1914). Later, Berland
(1924) identified nine spider morphospecies including the discovery of the island’s only
known endemic spider, Tetragnatha paschae Berland 1924 (Berland 1924). Interestingly,
this species has been observed only once since its initial discovery nearly a century ago.
Using a combination of existing museum collections and field data, Baert et al. (1997)
compiled a list of 36 spider morphospecies known to occur on the island, which included
Berland’s (1924) work. With the exception of two morphospecies identified by Baert et
al. (1997), T. paschae and “Orchestininae gen. n., sp. n.” (Family Oonopidae), all spiders
likely represented nonnative alien species. This possible new genus and species was part
of Lehtinen’s (1988) unpublished collection and has yet to be formally described (P.
Lehtinen, in litt.).
Our objectives were to rediscover T. paschae, identify additional endemic spider
species on the island, and summarize the current knowledge of spiders on Rapa Nui.
Specifically, we conducted an island-wide baseline survey including the first inventories
of cave ecosystems and Motu Nui (a small islet off the southwestern coast of the island).
We also developed an annotated list of spider species known to occur on Rapa Nui and
outlined a strategy for future research and monitoring.
METHODS
Study Area. Located 3,512 km west of South American coast and 3,400 km south by
southeast of the Pitcairn Islands, Rapa Nui, a Polynesian island under the administration
of Chile, is approximately 164 km2. Rapa Nui and its islets are volcanic and have a mar-
itime subtropical climate. Today, the vegetation of Rapa Nui is primarily grassland with
nonnative stands of Eucalyptus spp. trees with some native and indigenous vegetation pri-
marily within and surrounding the three crater lakes.
We sampled 15 different locations across the island including both agrarian and
undeveloped landscapes (Fig. 1). The Appendix provides study site place names, individ-
ual study site locations with their associated coordinates, and a description of the methods
applied per study site. With the exception of Motu Nui and the Roiho lava tube caves, the
general localities of our study areas overlap with Baert et al. (1997).
BISHOP MUSEUM OCCASIONAL PAPERS: No. 120, 2017
2
Study Sites
Ahu Akivi: Two separate areas adjacent to Ahu Akivi were sampled. One (Aki 1) was
within invasive guava trees and shrubs, while the second (Aki 2) was within a mono-
culture stand of Eucalyptus sp.
Akahanga: We sampled an open grassland area heavily grazed by horses and cattle.
Anakena: We sampled one area north of Anakena beach along the rocky coast. This grass-
land consisted primarily of invasive milkweed Asclepias curassavica L., was frequently
used by humans, and appeared heavily grazed by horses and cattle.
Ava Ranga Uka (an intermittent stream): We searched for spiders in two areas along the
banks of the small intermittent stream channel (Ava 1 and 2) and one area within the
entrance of a cave (Ava 3). Standing water was present within the channel during our sam-
pling effort. The banks of this intermittent stream were characterized with grasses includ-
ing Cyperus eragrostris Lam. and Melinis minutiflora P. Beauv.
Cotoras et al.—Spiders of Rapa Nui 3
Figure 1. Fifteen study sites sampled across Rapa Nui from 2008 through 2012: Ahu Akivi [A],
Akahanga [B], Anakena [C], Ava Ranga Uka [D], Greenhouse at CONAF [E], Motu Nui [F], Ovahe
[G], Poike [H], Rano Aroi [I], Rano Kau [J], Rano Raraku [K], Roiho Lava Tube Caves [L], Te Ara
O Te Ao [M], Terevaka [N], and Vinapu [O]. Base map is a NASA ASTER DEM, courtesy of Jeff
Jenness.
Greenhouse, Corporación Nacional Forestal (CONAF) Headquarters: We sampled one
location near the greenhouse buildings of Oficina Provincial Parque Nacional Rapa Nui,
CONAF. Within this area, there were several Polynesian endemic tree species (including
Hibiscus rosa-sinensis L. and the functionally extinct Sophora toromiro (Philippi)
Skottsberg) adjacent to a landscaped area of manicured grasses and ornamental plants.
Motu Nui: This islet is located off the southwestern coast of Rapa Nui. We randomly
searched Motu Nui for spiders. Primary grassland association was Paspalum fosterianum
Flüggé and Cyperus polystachyos Rottb. with other less dominant grass species including
Sporobolus indicus (L.) R. Br., Bromus catharticus Vahl, Cyperus eragrostris Lam.,
Portulaca oleracea L., Tetragonia tethragonoides (Pallos) Kuntze, and Chamaesyce ser-
pens Kunth (P. Lazo Hucke, in litt.).
Ovahe: We sampled two areas near Ovahe beach. One area (Ova 1) was along the rocky
shoreline within both rocks and grassland, while the second area (Ova 2) occurred within
grassland and shrubs heavily grazed by livestock.
Poike: Poike (370 m elevation) is the second highest mountain and demarcates the south-
eastern corner of the Rapa Nui island triangle. We collected within three areas. Two areas
(Poike 1 and 2) were located within monoculture stands of Eucalyptus spp. adjacent to the
highly eroded area in the southeastern most extent of Poike. Our third site (Poike 3) was
located on the southern slopes of Maunga Vai a Heva, one of the three volcanic domes of
Poike. Grassland vegetation around the base of Maunga Vai a Heva includes Sporobolus
indicus (L.) R. Br.
Rano Aroi: We sampled one area within this crater. Vegetation was a Schoenoplectus cal-
ifornicus C.A. Mey. Steud. and Persicaria acuminate (Kunth) M. Gómez association.
Rano Kau: This volcano and its associated crater lake encompass the southwestern corner
of the Rapa Nui island triangle. Rano Kau crater supports the highest diversity of island
and Polynesian endemic plant species on the island (Dubois et al. 2012; Wynne 2016).
This area is largely isolated from human use and livestock grazing (Skottsberg 1953;
Wynne 2016), representing one of the most biologically important areas on the island
(Wynne 2016). We sampled three sites (Rkau 1 through 3) along the western slope of the
crater between the Rano Kau tourist overlook and the crater floor. Vegetation within these
areas consisted of a closed canopy of miro tahiti (Melia azedarach L.) with a fern under-
story including Microsorum parksii Copel. and Microlepia strigosa (Thunb.) C. Presl.
Rano Raraku: We sampled two areas (Rrar 1 and 2) along the edge of the crater lake.
Vegetation was primarily the indigenous reed (S. californicus) with the western boundary
supporting a distinct S. californicus – P. acuminate association.
Roiho Lava Tube Caves: Ten caves were sampled ~5 km north of the village of Hanga
Roa. The study area is characterized by gently rolling hills (i.e., extinct scoria cones) with
coastal cliff faces flanking the western-most boundary. Vegetation was grassland and
guava (Psidium guajava L.) shrub. Within the collapse pit and skylight entrances of most
4 BISHOP MUSEUM OCCASIONAL PAPERS: No. 120, 2017
caves, several alien and Polynesian tree species were present including fig (Ficus sp.),
avocado (Persea americana Mill.), apple banana (Musa ×paradisiaca L.), and roseapple
(Syzygium jambos (L.) Alston). Additionally, fern-moss gardens, an important relict habi-
tat (Wynne et al. 2014), occurred within several cave entrances and beneath cave sky-
lights. This habitat is characterized by a presumed cave-restricted endemic fern
(Blechnum paschale; DuBois et al. 2013) and several species of moss including at least
one endemic species (Fissidens pascuanus; Ireland & Bellolio 2002). Wynne et al. (2014)
suggests this habitat may have been somewhat insulated from intensive environmental
changes that occurred on the surface.
Te Ara O Te Ao: We sampled one area along the Te Ara O Te O trail between CONAF
headquarters and Rano Kau on the northern slope of the caldera. The site is situated within
an area intensively grazed by horses and cattle. Vegetation includes various grass species
and the invasive legume Crotalaria grahamiana Wight & Arn.
Terevaka: At 511 meters elevation, Terevaka is the highest mountain peak of the island,
demarcating the northern corner of the Rapa Nui island triangle. Grassland vegetation
included Axonopus paschalis (Stapf) Pilger, Dichelachne micrantha (Cav.) Domin,
Dichelachne crinita (L.f.) Hook. f., and Sporobolus indicus (L.) R. Br.
Vinapu: We sampled an area within a forest patch north of the paved road leading to Ahu
Vinapu trailhead. The forest patch consisted primarily of Casuarina equisetifolia L., M.
azedarach and P. guajava with the latter two species as dominant.
Sampling
Surface Sampling: Surface collecting was conducted by DC, CV and LF between 12
August and 02 September 2012. Sampling techniques included beating sheet, sifting leaf
litter, sticky paper traps, and opportunistic hand collecting. We used a 71 cm2canvas beat-
ing sheet (Bioquip Catalog #2840C) to extract spiders from plants. We held the beating
sheet below selected trees and scrubs, and then hit the plant several times. As the spiders
fell off the plant onto the sheet, they were collected. Leaf-litter was collected from select-
ed trees and scrubs (regardless of whether the plants were native or alien). We extracted
spiders and other insects from leaf litter using a Berlese funnel. At one study site, we
deployed one Olson Products Inc.®yellow sticky strip (13 × 7.5 cm) for six days. The spe-
cific methods applied at each site are provided in the Appendix.
Cave Sampling: Three research teams (led by JW) systematically sampled 10 caves for all
arthropods during three research trips (16–21 August 2008; 28 June–17 July 2009; and
01–07 August 2011). Four methods (pitfall traps, time-constrained searches, opportunistic
collecting, and timed direct intuitive searches) were applied. Pitfall traps consisted of two
946-ml stacked plastic containers (13.5 cm high, 10.8-cm-diameter rim and 8.9-cm base).
A teaspoon of peanut butter placed in the bottom of the exte rior container was used as bait.
The bottom of the interior container had several dozen holes to allow the bait to “breathe”
to attract arthropods. Traps were deployed for three to four days. Although pitfall traps are
not specifically designed to attract spiders, arachnids were occasionally attracted to other
arthropods ensnared in the pitfall traps and were also collected.
5
Cotoras et al.—Spiders of Rapa Nui
Time-constrained searches involved estimating a one-meter radius around each pit-
fall trap sampling station and then conducting a timed search. Searches were con ducted
for one to three minutes (one minute if no arthropods were observed, three if arthropods
were detected) before pitfall trap deployment and prior to trap removal.
Opportunistic collection involved collecting arthropods as encountered – while
deploying and removing pitfall traps, and before and after timed searches. Personnel also
searched the ground, walls and ceilings as they walked the length of each cave. In five
caves (where all the collecting methodologies were applied), we also conducted timed
direct intuitive searches (DIS) of fern-moss gardens by gently combing through the fern
and moss and looking beneath rocks for 40 search-minutes per garden (two observers ×
20 minutes per observer). In four additional caves, we limited sampling to DIS within
fern-moss gardens only (two observers ×20 minutes per observer). In 2011, the deep
zones of four caves were further sampled via bait sampling and DIS. Three types of baits
were placed directly on the ground and within cracks and fissures on cave walls, ceilings
and floors: sweet potato (Ipomoea batatas), chicken and fish entrails, and small branches
of hibiscus (Hibiscus rosa-sinensis) and Ngaoho (Caesalpinia major) shrubs. Two to three
stations of each bait type were deployed, for four to five days, within the deep zone(s) of
each cave. At proximity to bait sampling arrays, we also conducted one DIS by searching
the cave floor for 10 minutes within a 1m2area.
Collection,Curation and Taxonomy
Spiders collected during the surface sampling effort were preserved in 95% ethanol.
Specimens were identified to the lowest taxonomic level possible using Baert et al.
(1997), Ubick et al. (2009), and Bradley (2012). Voucher specimens will be deposited at
Museo Nacional de Historia Natural, Santiago, Chile.
Cave specimens were preserved in 75 to 95% ethanol. Cave-dwelling spiders were
identified using a combination of voucher specimens from the Bishop Museum, Honolulu,
HI and species’ lists. Voucher specimens for most species are deposited at the Bishop
Museum and Museo Antropológico P. Sebastian Englert on Rapa Nui.
We applied the following rules to summarize our results and develop an island-wide
annotated species list. For our results, when comparing species and family richness across
study sites, coarse level identifications (i.e., at family and genus level) were retained. For the
annotated species list, coarse identifications (i.e., family and genus level) were included only
if they represented a unique family or genus for the island. If the coarse identification within
a given family or genus contained more than one species, it is possible the coarse level iden-
tification represents an existing species and was removed. However, if there was only one
morphospecies identified within a given family or genus, the record was retained and pre-
sumed to be unique. The World Spider Catalog (WSC 2016) was used to confirm validity
of taxonomy.
RESULTS
We detected 26 unique morphospecies (representing 15 families and at least 20 genera;
Table 1) contributing to the total of 47 spider morphospecies known for Rapa Nui (Table
2). At least six new island records were identified including Coras sp. (Amaurobiidae),
Lepthyphantes sp. (Linyphiidae), Sanogasta maculatipes (Keyserling, 1878), Scytodes
globula Nicolet, 1849, Scytodes fusca Walckenaer, 1837, and Steatoda cf. erigoniformis
(Pickard-Cambridge, 1872).
6 BISHOP MUSEUM OCCASIONAL PAPERS: No. 120, 2017
7
Cotoras et al.—Spiders of Rapa Nui
Table 1. Spider morphospecies detected during this study per study site.
Family Morphospecies Study Sites*
A B C D E F G H I J K L M N O
AGELENIDAE Tegenaria domestica (Clerck, 1757) X X X X X X X
AMAUROBIIDAE Coras sp. X
ANYPHAENIDAE Sanogasta maculatipes (Keyserling, 1878) X X
ARANEIDAE Araneidae sp. X
CORINNIDAE Creugas gulosus Thorell, 1878 X
GNAPHOSIDAE Gnaphosidae sp. X X X
LINYPHIIDAE Lepthyphantes sp. X
Tenuiphantes tenuis (Blackwall, 1852) X X
OECOBIIDAE Oecobius navus Blackwall, 1859 X X
OONOPIDAE Oonopidae sp. X X X
PHOLCIDAE Holocnemus cf. piritarsis Berland, 1942 X X
Smeringopus pallidus Moenkhaus, 1898 X X
SALTICIDAE Salticidae sp. X
Habronattus coecatus (Hentz, 1846) X
Hasarius adansoni (Audouin, 1827) X X X X X
Opisthoncus cf. mordax Koch, 1880 X
Plexippus paykulli (Audouin, 1826) X
Phidippus regius Koch, 1846 X X
SCYTODIDAE Scytodes fusca Walckenaer, 1837 X
Scytodes globula Nicolet, 1849 X X
Scytodes longipes Lucas, 1844 X X X
TETRAGNATHIDAE Tetragnatha sp. X
THERIDIIDAE Thereidiidae sp. X
Latrodectus geometricus Koch, 1841 X X X X X X X
Parasteatoda tepidariorum (Koch, 1841) X X X X X X X
Steatoda grossa (Koch, 1838) X X X
Steatoda cf. erigoniformis
(Pickard-Cambridge, 1872) X
TRACHELIDAE Meriola arcifera (Simon, 1886) X
*Ahu Akivi [A], Akahanga [B], Anakena [C], Ava Ranga Uka [D], Headquarters at CONAF [E], Motu Nui [F], Ovahe [G], Poike [H], Rano Aroi [I], Rano Kau [J],
Rano Raraku [K], Roiho Lava Tube Caves [L], Te Ara O Te Ao [M], Terevaka [N], and Vinapu [O]. An “X” corresponds to the presence of a morphospecies at a
study site.
BISHOP MUSEUM OCCASIONAL PAPERS: No. 120, 2017
8
Table 2. Annotated list of spider morphospecies known from Rapa Nui.
Family,
Genus species Status Distribution Detections Taxonomy
Agelenidae
Tegenaria domestica
(Clerck, 1757) Alien Cosmopolitan 2
Amaurobiidae
Coras sp. Unk. Unknown 4
Anyphaenidae
*Gayenna maculatipes
(Keyserling, 1878) — 2 see S. maculatipes
Sanogasta maculatipes . Peru, Bolivia, Brazil,
(Keyserling, 1878) Alien Uruguay, Argentina, 4
Chile
Araneidae
Araneidae gen. sp. Unk. Unknown 3, 4
Araneus sp. Unk. Unknown
*Epeira sp. — 3 see Araneus sp.
Zygiella sp.? Unk. Unknown 2
Corinnidae
*Corinna cetrata (Simon, 1888) — 1 see Creugas gulosus
Creugas gulosus Alien Cosmopolitan 2, 4
Thorell, 1878
Gnaphosidae
Drassodes sp.? Unk. Unknown 1
Odontodrassus javanus Alien Myanmar to Japan, 2
(Kulczynski, 1911) Seychelles, New
Caledonia, Jamaica
Urozelotes rusticus
(Koch, 1872) Alien Cosmopolitan 2
Linyphiidae
Lepthyphantes sp. Unk. Unknown 2, 4
Ostearius melanopygius
(Pickard-Cambridge, 1879) Alien Cosmopolitan 2
Tenuiphantes tenuis Palearctic (elsewhere,
(Blackwall, 1852) Alien introduced) 2, 4
Ochyroceratidae
Theotima minutissima
(Petrunkevitch, 1929) Alien Pantropical 2
Oecobiidae
Oecobius navus
Blackwall, 1859 Alien Cosmopolitan 2, 4
Oonopidae
*Gamasomorpha loricata
(Koch, 1873) — 2 see X. loricata
Opopaea silhouettei
(Benoit, 1979) Alien Seychelles 2
Orchestininae sp. End? Rapa Nui? 2
Xestaspis loricata Alien China, Taiwan, Laos,
(Koch, 1873) Micronesia, Australian
Pholcidae
Pholcus phalangioides
(Fuesslin, 1775) Alien Cosmopolitan 1, 2, 4
Smeringopus pallidus
Moenkhaus, 1898 Alien Cosmopolitan 2, 4
Holocneminus piritarsis
Berland 1942 Unk. Samoa, Austral Is.,
Henderson I., Marshall Is. 2, 4
Cotoras et al.—Spiders of Rapa Nui 9
Table 2. (continued)
Family,
Genus species Status Distribution Detections Taxonomy
Salticidae
Dendryphantes mordax Chile, Argentina,
(Koch, 1846) Unk. Uruguay 2
Habronattus coecatus USA, Mexico, 2, 4
(Hentz, 1846) Alien Bermuda
Hasarius adansoni
(Audouin, 1827) Alien Cosmopolitan 1, 2, 4
Menemerus bivittatus
(Dufour, 1831) Alien Pantropical 2
Plexippus paykulli
(Audouin, 1826) Alien Cosmopolitan 1, 2, 3, 4
Phidippus regius Koch, 1846 Alien USA, West Indies 2, 4
Scytodidae
Dictis striatipes Koch, 1872 Alien China to Australia 2
Scytodes fusca
Walckenaer, 1837 Alien Pantropical 4
Scytodes globula Bolivia, Brazil, 4
Nicolet, 1849 Alien Argentina, Uruguay, Chile
Scytodes longipes
Lucas, 1844 Alien Pantropical 2, 4
Scytodes lugubris
(Thorell, 1887) Alien Pantropical 1
Sicariidae
Loxosceles laeta Alien America, Finland,
(Nicolet, 1849) Australia 2
Tetragnathidae
Tetragnatha sp. End.? Rapa Nui? 4
Tetragnatha mandibulata West Africa, India to 3
Walckenaer, 1842 Alien Philippines, Australia
Tetragnatha nitens
(Audouin, 1825) Alien Pantropical 1, 2
Tetragnatha paschae
Berland, 1924 End. Rapa Nui 1
Theridiidae
*Coleosoma adamsoni
Berland, 1934 — 2 see P. mneon
Coleosoma floridanum
Banks, 1900 Alien Pantropical 2
Cryptachaea blattea
(Urquhart, 1886) Alien Cosmopolitan
Latrodectus geometricus
Koch, 1841 Alien Cosmopolitan 2, 4
Nesticodes rufipes
(Lucas, 1846) Alien Pantropical 2
*Parasteatoda acoreensis
(Berland, 1932)? — 2 see C. blattea
Parasteatoda tepidariorum
(Koch, 1841) Alien Cosmopolitan 2, 4
Platnickina mneon
(Bösenberg & Strand, 1906) Alien Pantropical
Steatoda grossa (Koch, 1838) Alien Cosmopolitan 4
*Stearodea grossa
(Koch, 1838) — 2 see S. grossa
We did not find Tetragnatha paschae during our study. However, we did collect spec-
imens of a potentially undescribed Tetragnatha species within the S. californicus reeds
along the lake shore of Rano Raraku. This Tetragnatha sp. was not found in other study
sites, nor was it reported in earlier studies. The Tetragnatha sp. specimens were morpholog-
ically distinct from T. paschae Berland, 1924, T. nitens (Audouin, 1826), and T. mandibula-
ta Walckenaer, 1842. For the comparison with T. paschae, we used the original description
and voucher specimens from the Natural History Museum of London. Our specimens did
not represent any known Chilean Tetragnatha species (Nicolet 1849; Keyserling 1865), nor
did they resemble Tetragnatha species described from other Pacific Islands (R. Gillespie,
pers. comm. 2013).
Distributional patterns of Rapa Nui spider species included three likely endemic
morphospecies with the remaining spider morphospecies introduced to the island from
other parts of the world (Table 3). Nearly half of the spiders known to Rapa Nui have
either a cosmopolitan or pantropical (13 and 10 species, respectively) distribution. Two
species were identified as distributed across Polynesia and four species are known from
South America.
BISHOP MUSEUM OCCASIONAL PAPERS: No. 120, 2017
10
Table 2. (continued)
Family,
Genus species Status Distribution Detections Taxonomy
Theridiidae (continued)
Steatoda cf. erigoniformis
(Pickard-Cambridge, 1872) Alien Pantropical 4
Theridion buxtoni
Berland, 1929 Unk. Samoa, Henderson Is.,
Tuamotu Arch. 2
*Theridion tepidariorum
(Koch, 1841) — 1 see P. tepidariorum
Trachelidae
Meriola arcifera (Simon, 1886) Unk. Chile, Bolivia, Argentina, 2, 4
USA (introduced),
Hawaii
Family- and genus-level identifications were included if they represented a unique detection for a given family or
genus; if there were multiple species within a given family or genus, these records were removed. Status is endemic
(End.), alien (Alien), or unknown (Unk.). “Endemic” is for morphospecies believed to occur only on Rapa Nui,
while “alien” is used for species introduced to the island intentionally or accidentally by humans. We use
”unknown” when there was not enough information to confidently place the morphospecies in one of the other two
categories. Taxonomy was validated using WSC (2016). Taxonomy contains changes to the scientific names. When
an asterisk (*) appears before a species name, go to the taxonomy column for direction to the valid taxonomic name.
Distribution refers to the spider’s known geographic distribution, and when available, we used distribution infor-
mation from WSC (2016). Detections represent the studies during which the morphospecies was detected: [1]
Berland, 1924; [2] Baert et al., 1997; [3] Fuentes, 1914; and, [4] this study. Baert et al. (1997) presented a list of
morphospecies, which included those detected by Berland (1924); however, we listed species identified by Baert et
al. (1997) and Berland (1924) independently. Specimens from Araneidae gen. sp. were identified by Fuentes (1914)
and in this study; in keeping with our decision rules, we listed it as the same morphospecies. Baert et al. (1997)
misspelled Steatoda grossa as “Stearodea grossa”; we made the correction in this list.
There was one endemic species (T. paschae) and two potentially endemic species
(Orchestininae sp. and Tetragnatha sp.), 33 morphospecies believed to represent alien
species, and 11 morphospecies identified as “unknown”. For six of these species (two
species known from greater Polynesia and four species from South America), we were
uncertain whether their occurrence represents recent human introductions or natural col-
onization events. If the former, these species would be considered alien, while if the latter
they would be categorized as indigenous. The remaining five morphospecies with
“unknown” distributions were placed in this category because they could not be identified
beyond family or genus level. Plexippus paykulli (Audouin, 1826) was introduced over
100 years ago (Fuentes 1914) and represents a well-established alien species as it has
been documented in all subsequent spider studies (Berland 1924; Baert et al. 1997; this
study).
Study sites with the highest species richness were Roiho lava tube caves (n = 10),
Rano Kau (n = 9), and Poike (n = 7). Lowest richness was recorded at Akahanga and
Anakena with one morphospecies each, while Ahu Akivi, Motu Nui, Rano Aroi, and
Terevaka yielded two morphospecies each. Richness per study site at the species and fam-
ily level is provided in Table 4. Images of select spider species are presented in Fig. 2.
We detected three spider species in nearly half of our study areas. One agelenid spi-
der, Tegenaria domestica (Clerck, 1757) and two theridiid spiders, Latrodectus geometri-
cus Koch, 1841 and Parasteatoda tepidariorum (Koch, 1841), were detected across seven
study sites.
DISCUSSION
With the exception of three morphospecies (Tetragnatha sp., the potentially extinct T.
paschae, and Orchestininae gen. n., sp. n.?), the remaining 47 morphospecies are probably
alien species. Our work also yielded 14 species previously identified species by Baert et
al. (1997) and contributed at least six new island records. The latter represents an impor-
tant contribution for monitoring the influx of nonnative alien species, as well as providing
a more complete picture of the island’s arthropod community.
11
Cotoras et al.—Spiders of Rapa Nui
Table 3. Number of morphospecies by geographic distribution based on the anno-
tated list of known spider morphospecies of Rapa Nui.
Distribution
Number of Morphospecies 3 13 10 2 4 2 2 5 6
*Both endemic and possible endemic species were considered “endemic” in this table.
Endemic*
Cosmopolitan
Pantropical
North America/
Caribbean
South America
Polynesia
Asia
Other
Unknown
BISHOP MUSEUM OCCASIONAL PAPERS: No. 120, 2017
12
Table 4. Number of spider families and morphospecies detected per study site.
Study Sites*
Taxonomic Groups A B C D E F G H I J K L M N O
Family 2 1 1 4 3 2 5 4 2 6 5 6 6 2 3
Morphospecies 2 1 1 4 3 2 6 6 2 9 6 10 7 2 3
Figure 2. Examples of the spiders of Rapa Nui: [A] Smeringopus pallidus (♀) with egg sac from a
cave in Roiho (alien species); [B] Tetragnatha sp. (♀; possibly an undescribed endemic species); [C]
Steatoda grossa (♀; alien species); and, [D] ventral view of Latrodectus geometricus (♀; alien
species). Specimens in B through D may be slightly discolored due to being curated in 70% isopropyl
alcohol. Images courtesy Dan Ruby (A), Sebastian Yancovic Pakarati (B), and Byron Yeager (C, D).
*Ahu Akivi [A], Akahanga [B], Anakena [C], Ava Ranga Uka [D], Greenhouse at CONAF [E], Motu Nui [F], Ovahe
[G], Poike [H], Rano Aroi [I], Rano Kau [J], Rano Raraku [K], Roiho Lava Tube Caves [L], Te Ara O Te Ao [M],
Terevaka [N], and Vinapu [O].
The Tetragnatha sp. identified from Rano Raraku appears undescribed and may rep-
resent a new endemic species. Upon examination of Berlands (1924) description of T.
paschaeand specimens from the Natural History Museum of London, we found the
Tetragnatha sp. specimens collected from Rano Raraku do not fit the morphological
descriptions of T. paschae and is distinct from other known Tetragnathaspecies from
Chile and other Pacific islands. Lehtinen (1995) identified Tetragnathidae as one of the
first families to colonize Polynesia originating from South America or Hawaii.
Gillespie (2002) found no phylogenetic evidence of an adaptive radiation event involving
a single common ancestor diversifying across Polynesia. Additional taxonomic and
genomic work will be required to describe this species, as well as to more fully address
these biogeographical uncertainties.
The study sites with the highest spider diversity warrant further examination. Roiho
lava tube caves (n = 10) exhibited the highest diversity across all study areas. We offer
two possible explanations. Firstly, sampling intensity was much higher in Roiho than at
all the other study sites. Thus, our conclusion that Roiho caves contained the highest
diversity may be due to sampling intensity. However, it may also be a result of higher spa-
tial heterogeneity when compared to our other study sites. Rapa Nui caves support numer-
ous microhabitats including: fern-moss gardens within cave entrances and beneath cave
skylights (Wynne et al.2014); cracks, crevices and pore spaces within rock piles, cave
walls and ceilings; mud covered floors; and, plant roots infiltrating the deepest portion of
some cave passages. The occurrence of these microhabitats combined with the environ-
mental zonal gradient common to the largest caves (i.e., photosynthetic zone to cave deep
zone; Howarth 1980, 1982) results in a comparatively higher level of habitat heterogene-
ity. Because high habitat heterogeneity is an important variable driving high species rich-
ness of various arthropod groups (Gardner et al.1995; Humphrey et al.1999;Hansen
2000), we suggest, high spider diversity observed in Roiho caves may also be a product
of high habitat heterogeneity at these sites.
Rano Kau (n = 9) supported the second highest spider diversity. This result may also
be attributed to high habitat heterogeneity associated with higher habitat complexity and
plant species diversity. Extending at least 172 m from the floor to rim, the crater walls
receive varying degrees of insolation given aspect, time of day and season, and the interior
is characterized by large boulder fields, vertical cliff faces, and dense vegetation ranging
from thick grassland to forest with a Schoenoplectus californicus Persicaria acuminate
plant association within and surrounding the crater lake (Wynne 2016). Dubois et al.
(2013) has listed at least 12 endemic or indigenous plants and at least five Polynesian-
introduced plant species known to occur within Rano Kau. Vegetation in the other surface
study sites were comparatively depauperate.
Three widely dispersed alien species on Rapa Nui, T. domestica, L. geometricus, and
P. tepidariorum are associated with human activities and structures. Also, T. domestica
and L. geometricus have cosmopolitan distributions globally, while P. tepidariorum is
widely distributed across North America and Europe (WSC 2016). Thus, we are not sur-
prised by the distributions of these species. Comparatively, Steatoda grossa (Koch, 1838)
was detected in three of 14 study areas. This species has a cosmopolitan distribution
(WSC 2016) and is also associated with human structures.
There are several environments that have been sampled minimally or remain unex-
amined. Wynne (2016) completed a baseline inventory of ground-dwelling arthropods on
Cotoras et al.—Spiders of Rapa Nui 13
cliffs, caves, and crater lakes of Rapa Nui. Although the most extensive effort to date, only
a fraction of these environments were sampled. Cliff habitats likely support one of the
most important relict habitats on the island. As evidenced from other islands, these envi-
ronments could be relictual sites for endemic plant (Wood 2012) and arthropod (Priddel
et al. 2003) species. On Rapa Nui, cliffs remain largely inaccessible to humans, most live-
stock, and certain sections may be even inaccessible to rats. Regarding caves, only 30 of
the at least 800 known caves have been sampled (Wynne et al. 2014; Wynne 2016). Thus,
this work is far from complete. Additional surveys should be conducted in the crater lakes.
Wynne (2016) suggests the interior of Rano Kau represents another high priority site for
inventory, conservation and management of endemic arthropods. Finally, the neighboring
islets of Rapa Nui may hold great promise for additional new endemic species discoveries
(Wynne 2016). Motu Nui was not intensively sampled during this study, and the remain-
ing islets have not been examined.
Additional work within these environments will be required to further guide conser-
vation and management decisions, better define distributional ranges of target species, and
provide critical monitoring information of arachnids likely predating upon endemic
species. Data collected during such an effort will provide natural resource managers with
some of the information required to develop management plans for protection and moni-
toring of endemic arthropod species’ populations.
Additional research efforts will also serve to better define the distribution of
Tetragnatha sp. as we suggest this spider may prove to be an important management
species. Wynne et al. (2014) suggested the 10 endemic presumed cave-restricted species
may be endangered due to a number of factors including an arthropod community domi-
nated by alien species, and the subsequent predation and competition with alien species.
Thus, further research may also serve to monitor alien arachnid species that may directly
threatened Rapa Nui’s limited endemic arthropods, as well as provide information on the
distribution and autecology of the only possible extant endemic spider (Tetragnatha sp.).
An intensive island-wide survey in the areas mentioned will likely reveal additional new
endemic species including arachnids, and broaden our understanding of the natural history
of the most isolated island in Polynesia.
ACKNOWLEDGMENTS
We thank Graciela Campbell, Ninoska Cuadros, Omar Durán Veriveri, Pedro Hito, Pedro
Lazo Hucke, Sergio Manuheuroroa, Raúl Palomino Matta, Hotu Paté, Carlos Salinas, John
Tucki, and Enrique Tucki of CONAF-Parque Nacional Rapa Nui, and the Armada de Chile.
Anthony Dubois also facilitated the field collections. Permits for surface sampling were
secured through Lynne Hollyer (UC Berkeley Industry Alliances Office), Enrique Tucki
(Parque Nacional Rapa Nui, CONAF) and Javiera Mesa (CONAF V Región). Taxonomic
guidance was provided by Abel Bustamante, Rosemary Gillespie, Charles Griswold, and
Darrell Ubick. Frank Howarth, Bishop Museum, assisted with identifications of spiders
from caves. Léon Baert provided guidance with expedition planning of surface sampling.
Pedro Lazo Hucke and Sebastián Yancovic Pakarati kindly provided information regarding
plant associations for several of the study sites. Pedro Lazo Hucke insured the correct
spellings of Rapa Nui plant names. Christina Colpitts, Lynn Hicks, Bruce Higgins, Alicia
Ika, Talina Konotchick, Scott Nicolay, Knutt Petersen, Lázero Pakarati, Victoria Pakarati
BISHOP MUSEUM OCCASIONAL PAPERS: No. 120, 2017
14
Hotus, Pete Polsgrove, Dan Ruby, and Liz Ruther provided field support to JW. We thank
Jan Beccaloni and the Natural History Museum of London for loaning us specimens of T.
paschae. Jeff Jenness, Jenness Enterprises, provided the ASTER-derived DEM base map
used in Figure 1. Gustavo Hormiga and an anonymous reviewer contributed to the improve-
ment of this manuscript. This work was partially supported by Tinker Grant (Center for
Latin American Studies, UC Berkeley) and Fulbright/CONICYT fellowship to DC and
Projecto CONICYT grant number 79100013 to CV and LF. The Explorers Club Expedition
Fund and the National Speleological Society’s International Exploration Fund partially sup-
ported the work of JW.
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APPENDIX. Study sites, sampling areas, coordinates, and methods applied during
spider sampling conducted on Rapa Nui.
Cotoras et al.—Spiders of Rapa Nui 17
Study Sites Sampling Coordinates Methods
Areas
Akahanga 27°09’58.26”S, 109°24’02.77”W BS, OPP
Anakena 27°03’50.81”S, 109°20’36.12”W OPP
Ahu Akivi Aki 1 27°07’56.27”S, 109°24’09.95”W BS, OPP
Aki 2 27°07’24.37”S, 109°23’55.19”W BS, OPP
Ava Ranga Uka Ava 1 27°05’56.57”S, 109°22’15.45”W OPP
Ava 2 27°05’50.22”S, 109°22’21.64”W OPP
Ava 3 27°06’06.81”S, 109°22’13.09”W OPP
Greenhouse,
CONAF Hdqrtrs 27°09’55.98”S, 109°26’23.12”W BS, OPP, LS
Motu Nui 27°12’00.79”S, 109°27’11.13”W OPP
Poike Poike 1 27°06’46.45”S, 109°14’20.62”W BS, OPP
Poike 2 27°06’49.66”S, 109°14’20.95”W BS, OPP
Poike 3 27°05’58.61”S, 109°15’09.02”W BS, OPP
Ovahe Ova 1 27°04’15.29”S, 109°18’57.17”W OPP
Ova 2 27°04’36.37”S, 109°19’07.21”W BS, OPP
Rano Aroi Raroi 1 27°05’35.52”S, 109°22’29.09”W BS, OPP, LS
Rano Kau Rkau 1 27°10’50.46”S, 109°26’21.29”W BS, OPP
Rkau 2 27°10’53.68”S, 109°26’16.56”W BS, OPP
Rkau 3 27°10’55.14”S, 109°26’16.35”W BS, OPP
Rano Raraku Rrar 1 27°07’23.80”S, 109°17’24.57”W OPP, LS
Rrar 2 27°07’15.47”S, 109°17’16.00”W OPP, LS
Roiho Lava Tube
Caves 27°6'25.81''S, 109°24'42.786''W DIS, Bait, OPP,
PT
Te Ara O Te Ao 27°10’26.30”S, 109°26’29.71”W BS, OPP, SP
Teravaka 27°05’21.23”S, 109°22’26.89”W OPP
Vinapu 27°10’10.27”S, 109°23’01.22”W BS, OPP
We applied several techniques including beating sheets (BS), leaf litter sifting (LS), and sticky paper
(SP) for surface environments; and bait sampling (Bait), pitfall trapping (PT), and direct intuitive search-
es (DIS) for caves. We opportunistically searched (OPP) at all study sites.
... Based on the body measurements that are reported in this description [9], Baert placed it among the largest species of the genus [8]. The third Tetragnatha species on Rapa Nui has only recently been observed in a survey of spiders in 2012 by Cotoras et al. [14]. The species is morphologically distinct from Tetragnatha species that are known to inhabit other Pacific Islands and Chile (the two most likely sources of human introduction), and it has therefore been hypothesized that it may represent a second endemic Tetragnatha species on Rapa Nui [14]. ...
... The third Tetragnatha species on Rapa Nui has only recently been observed in a survey of spiders in 2012 by Cotoras et al. [14]. The species is morphologically distinct from Tetragnatha species that are known to inhabit other Pacific Islands and Chile (the two most likely sources of human introduction), and it has therefore been hypothesized that it may represent a second endemic Tetragnatha species on Rapa Nui [14]. The 2012 survey also found no evidence of T. paschae or T. nitens, despite covering a wide range of environments and geographic locations. ...
... The 2012 survey also found no evidence of T. paschae or T. nitens, despite covering a wide range of environments and geographic locations. Since the 1993 survey by Baert et al. also found no evidence of T. paschae [9], it has been hypothesized that T. paschae is now extinct [9,14]. ...
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... Also due to its remoteness, it has received relatively little attention in terms of documentation of its terrestrial biodiversity. It is only in the last few years that there has been a series of publications describing new species Wynne 2013, Taiti andWynne 2015) and on resurveying of the island (Cotoras et al. 2017) and developing habitat restoration projects (Dubois et al. 2013). That research has provided better evidence of the critical state of the island flora and fauna but has also presented unexpected discoveries ( Wynne et al. 2014). ...
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