tiny island rather than having having rafted directly than across tiny rather island nearly the 2,000

transport of reptiles directly to the Marianas from source islands such as New New as such islands source from Marianas the to directly reptiles of transport

with the Australasian area, prevailing oceanic currents would not promote waif waif promote not would currents oceanic prevailing area, Australasian the with

isolated relative to other island masses. Although its biogeographic affinities are are biogeographic affinities its Although masses. island other to relative isolated

the uninhabited Farallon de Pajaros Pajaros de Farallon uninhabited the

The chain extends northward approximately 800 km from Guam (13° 13' N) to to 13' N) (13° Guam from 800 km approximately northward extends chain The

Guam from larger islands in Australasia. Australasia. in larger islands from Guam

Guinea. Thus, it is likely that colonizing species have spread from tiny island to to island tiny from spread species have colonizing likely is that it Thus, Guinea.

Micronesica Micronesica

penish, penish,

The Mariana Islands are a line of small islands in the western Pacific Pacific western the Ocean. in islands of small line a are Islands Mariana The

rml rmt. oe aie pce per o ae elnd r dis­ or declined have to appear species native Some remote. tremely

o nlec seisrcns, ehp bcue l te sad ae ex­ are islands the all because perhaps richness, species influence to

the smaller northern islands. Proximity to source areas does not appear appear not does areas source to Proximity islands. northern smaller the

endemic. Species richness declines from the larger southern islands to to islands southern larger the from declines Species richness endemic.

lands. Because the islands are so isolated, all of the Marianas' reptile reptile Marianas' the of all isolated, so are islands the Because lands.

sninhv rdcd e itiuin eod frte ain Is­ Mariana the for records distribution new produced have Asuncion

Abstract-Recent Abstract-Recent

appeared as a result of the introduction of exotic snakes and lizards. lizards. and snakes exotic of introduction the of result a as appeared

species are necessarily excellent dispersers. Only Only dispersers. excellent necessarily are species

' Present address: Wildlife Resources Program, Yakima Indian Nation, P.O. Box 151, 151, Box P.O. Nation, Indian Yakima Program, Resources Wildlife address: Present '

Guam, Aguijan, Saipan, Anatahan, Guguan, Alamagan, Agrihan, and and Agrihan, Alamagan, Guguan, Anatahan, Saipan, Aguijan, Guam,

The Distributional Patterns of Reptiles and Amphibians in the the in Amphibians and Reptiles of Patterns Distributional The

WA 98948 98948 WA

24(2): 24(2): 195-210, 1991

210 Biological Sciences East, University of Arizona, Tucson, AZ 85721 85721 AZ Tucson, of Arizona, University East, Sciences Biological 210

U.S. Fish and Wildlife Service, National Ecology Research Center Center Research Ecology National Service, Wildlife and Fish U.S.

Division of Fish and Wildlife, Department of Natural Resources Resources Natural of Department Wildlife, and Fish of Division

National Museum of Natural History, Washington, DC 20560 20560 DC Washington, History, Natural of Museum National

Arizona Cooperative Fish and Wildlife Research Unit Unit Research Wildlife and Fish Cooperative Arizona

collections of reptiles and amphibians on Cocos, Cocos, on amphibians and reptiles of collections

GORDON GORDON

JAMES JAMES

THOMAS THOMAS

Mariana Islands Islands Mariana

Saipan, MP 96950 96950 MP Saipan,

Introduction Introduction

(= (=

D. D.

and and

H. H.

H. H.

REICHEL

Uracas, 21 21 Uracas,

RODDA RODDA

FRITTS FRITTS

1 1

° °

30' N). The archipelago is is archipelago The N). 30'

Emoia slevini slevini Emoia

km km

separating separating

is an an is Top­ 196 Micronesica 24(2), 1991

The biogeography of island reptiles has been critically examined with ref­ erence to islands near Indonesia (Cogger et al. 1983), Papua New Guinea (Heat­ wole 1975), and in the Caribbean (e.g., Levins & Heatwole 1963). However, little attention has been directed to remote oceanic chains such as the Marianas. The catastrophic loss of vertebrate species associated with the introduction of the Brown Tree Snake Boiga irregularis on Guam (Savidge 1987, Fritts 1988), has stimulated herpetological interest in the Mariana Islands. Elsewhere we will ana­ lyze the impacts of Boiga on the native lizards of Guam. In this work, we report a variety of new reptile records for the Marianas, summarize what is presently known about the distribution of reptiles and amphibians in the Marianas, and compare the Mariana Islands' observed distributional patterns with those that might be expected based on generalities derived from continental islands.

Methods During 1988 and 1989 we used standard herpetological collecting techniques to obtain reptile and amphibian specimens from various islands in the Marianas: Cocos, Guam, Rota, Aguijan, Tinian, Saipan, Anatahan, Guguan, Alamagan, Pagan, Agrihan, Asuncion, and Maug. Most specimens were captured by hand or with adhesive traps. All specimens were verified and deposited in the U.S. National Museum or the Museum of Southwestern Biology, University of New Mexico. A conscious effort was made to sample as many different habitats as possible on each island, but the sampling was not designed to quantify island­ wide populations. Our intent was to quantify populations at particular sites and to verify the presence of species. An island was considered well surveyed if a professional herpetologist had intensively collected the island at least once. For a collection to be considered intensive, it had to cover the full range of habitats present on the island, include both day and night sampling, and use at least one method other than visual censusing. The larger, more diverse islands required greater sampling effort. The four large southern islands of Guam, Rota, Tinian, and Saipan have been sampled repeatedly by many herpetologists.

Island Occurrences The current status of island records for reptiles and amphibians in the Mar­ ianas is shown in Table 1. Twenty-four new records verified by our specimens are indicated with an "a". The previous records are based on Crombie (unpub. data), Wiles et al. ( 1989), and Wiles et al. ( 1990). The new records for E. s/evini expand its known range from just Guam/Cocos to almost the entire Mariana chain. The other new island records are less surprising, and help solidify the distributional patterns analysed below. The nine questionable records are as fol­ lows: 1) Several Varanus indicus have been purposely translocated to Cocos by a Guam resident (M. McCoid, pers. comm.). In addition, two captive Varanus are Table 1. Summary of known occurrences. An "x" indicates an established museum record; "a" indicates a record reported here for the first time; "?" denotes a questionable report for which a specimen has not been procured (each explained in text). Island names are listed from south to north by their first four letters; full island names are given in the Appendix. No data are available for omitted islands (e.g., Farallon de Medinilla, Uracas). Species are alphabetical within groupings.

Species Coco Guam Rota Agui Tini Saip Anat Sari Gugu Alam Paga Agri Asun Maug :;i:, 0 Amphibians i:,. .,i:,. B. marinus X X X X X ? ~ L. Jal/ax X ? i:, r:- Turtles E:: C. japonica ., X X X X X .,::i. E. imbricata X .,::, u, T. scripta X ? :;i:, Snakes -g_0 B. irregu/aris X R. braminus X X X X X X a X X 9." ~ Lizards (Gekkonidae) a::i. muti/ata s G. X X X X a X X a X a 5· ::, G. oceanica X X X X X X X a a H. frenatus a X X X X a X a L. lugubris X X X X X a a X X a N. pe/agicus X X X ? P. ate/es X X X X

'°....

indicus indicus V. V.

? ?

X X X X X X X X X X X X X X ? ? ? ? X X

(Varanidae) (Varanidae)

L smaragdina smaragdina L X X X X

noctua noctua L. L. a a ? ?

E . . slevini slevini

X X X X X X

X X a a

a a

'D 'D E . . cyanura cyanura

X X ::0 ::0

? ?

E . . caeruleocauda caeruleocauda

X X a a X X X X

a a

X X X X a a X X

::- a a X X X X

N N

E . . atrocostata atrocostata

X X ~ ~ X X

N N

C. poecilopleurus poecilopleurus C.

X X a a

X X X X

X X X X X X X X X X a a a a a a

X X ~ -

C.fusca C.fusca

a a X X

X X X X

n n = =

(Scincidae) (Scincidae)

a a

carolinensis carolinensis A . .

X X X X

X X ;:; · ·

E:: E:: (lguanidae) (lguanidae)

Species Species Coco Coco Guam Rota Rota Guam Agui Agui Tini Tini Saip Anat Sari Gugu Alam Paga Agri Asun Maug Maug Asun Agri Paga Alam Gugu Sari Anat Saip

Table Table 1. 1. Continued Continued

00 00 - 'D 'D

along rocky shorelines. This species possibly still occurs at the poorly sampled sampled poorly the at occurs still possibly species This shorelines. rocky along

for for

dense coastal scrub which is its preferred habitat. Furthermore, suitable habitat habitat suitable Furthermore, habitat. preferred its is which scrub coastal dense

ered the possibility that incomplete sampling might be responsible for some of of some for responsible be might sampling incomplete that possibility the ered

biologist for the Commonwealth of the Northern Mariana Islands. Islands. Mariana Northern the of Commonwealth the for biologist

occupied by by occupied

on both Cocos and Rota strongly suggests that it was once on Guam. The habitat habitat The Guam. on once was it that suggests strongly Rota and Cocos both on

did identify both both identify did documented observation by Thomas Fritts. Fritts. Thomas by observation documented

om ct o h US Fs ad idie evc i 18 n i a iia un­ similar a in and 1985 in Service Wildlife and Fish U.S. the of Scott Norm

times unreliable, no other species in the area could be mistaken for these animals. animals. these for mistaken be could area the in species other no unreliable, times

cilopleurus, cilopleurus,

from source areas. Following Heatwole (1975), we attempted to model observed observed model to attempted we (1975), Heatwole Following areas. source from

and and

southern end of Guam. A similar caveat would apply to to apply would caveat similar A Guam. of end southern

to influence the numbers of reptile species on islands: island area and distance distance and area island islands: on species reptile of numbers the influence to

Guam even if it is now extirpated. extirpated. now is it if even Guam

believed to have escaped from a resort on the island. We have seen at least two two least at seen have We island. the on resort a from escaped have to believed uate the thoroughness of collecting efforts. Two main variables have been found found been have variables main Two efforts. collecting of thoroughness the uate

cies on Cocos would have reached that tiny islet by way of its much larger larger much its of way by islet tiny that reached have would Cocos on cies isn 97 ae peitos bu seis ihes ht a b ue t eval­ to used be can that richness species about predictions makes 1967) Wilson

Turtles of all sizes have been seen, suggesting that the population is established. established. is population the that suggesting seen, been have sizes all of Turtles

the differences among islands. The theory of island biogeography (MacArthur & & (MacArthur biogeography island of theory The islands. among differences the

with a question mark because it is not known if this population is self-sustaining. self-sustaining. is population this if known not is it because mark question a with

its occurrence was documented. It is extremely wary and difficult to see in the the in see to difficult and wary extremely is It documented. was occurrence its

Carlia Carlia Jusca.

The Geus River is among the most likely sites on Guam where where Guam on sites likely most the among is River Geus The

is unlikely that the the that unlikely is

species richnesses using island area in hectares, maximum height of the island island the of height maximum hectares, in area island using richnesses species (Kami et al. 1974). Although the collectors retained no voucher specimens, they they specimens, voucher no retained collectors the 1974). Although al. et (Kami

individuals, but do not know if the population is self sustaining. sustaining. self is population the if know not do but individuals,

neighbor, Guam. Therefore, it seems likely that that likely seems it Therefore, Guam. neighbor,

oo. utemr, nboegahcl rud oe ol epc ta ay spe­ any that expect would one grounds biogeographical on Furthermore, Cocos.

occur, as the river drains into the Cocos lagoon, and and lagoon, Cocos the into drains river the as occur,

E. atrocostata atrocostata E.

Varanus Varanus indicus

Although we have no records of of records no have we Although

Before analyzing the distributional patterns revealed by Table 1, 1, consid­ we Table by revealed patterns distributional the analyzing Before

4) The call of a a of call The 4)

2) 2)

7-9) Island residents report the establishment of of establishment the report residents Island 7-9)

6) A A 6)

3) The record of of record The 3)

5) 5)

Emoia Emoia cyanura

Trachemys Trachemys scripta

Nactus Nactus pelagicus

which has not been collected on Guam in recent years. years. recent in Guam on collected been not has which

E. E. atrocostata

Thus Thus

E. cyanura cyanura E.

occurs only in an extremely narrow and discontinuous strip strip discontinuous and narrow extremely an in only occurs

E. cyanura cyanura E.

E. atrocostata atrocostata E.

on Alamagan and Agrihan. Although local reports are some­ are reports local Although Agrihan. and Alamagan on

Litoria Litoria fallax

Lipinia noctua noctua Lipinia

was reportedly collected in the Geus River valley on Guam Guam on valley River Geus the in collected reportedly was

Rodda Rodda

have been collected on Saipan, but the record is listed listed is record the but Saipan, on collected been have

Species-Area Relationships Relationships Species-Area

on Guam has been colonized by the introduced skink skink introduced the by colonized been has Guam on

was seen by Phil Glass on Saipan. Saipan. on Glass Phil by seen was

and and

et et al.:

record is a misidentification of of misidentification a is record

E. caeruleocauda caeruleocauda E.

Marianas Reptile Distribution Distribution Reptile Marianas

may have been displaced from Guam before before Guam from displaced been have may

on Saipan was heard by Phil Glass, wildlife wildlife Glass, Phil by heard was Saipan on

Emoia atrocostata Emoia atrocostata

from Rota is based on a sight record by by record sight a on based is Rota from

E. cyanura cyanura E.

from the valley. Therefore, it it Therefore, valley. the from

E. cyanura cyanura E.

from Guam, its existence existence its Guam, from

Bufo marinus marinus Bufo

Cryptoblepharus Cryptoblepharus poe­

once occurred on on occurred once

E. caeruleocauda. caeruleocauda. E.

E. E. cyanura

is common on on common is

on Pagan Pagan on

would would 199 199

= =

= =

(island (island area),

10

0.15). Compared Compared 0.15).

~ ~

all all reptiles (except island

If If

Steadman ( 1987) have have argued 1987) Steadman (

& &

(species (species richness) on log

10

0.002; all other other all variables 0.002; P

= =

Micronesica Micronesica 24(2), 991 I

0.875, P P 0.875,

where where area is measured in hectares. The predictions of this

Fig. 1, Table Table The Fig. 2]. exponent lower 1, in the computation for

= =

; ;

, ,

2 2

198

355

·

·

0

0

area)

The species-area relationship The relationship species-area empirically determined for by Heatwole (1975)

A A species was considered native if there were no indications of its arrival

The The relationship between island area and species abundance of reptiles may

l.42(island l.42(island area)

Marianas. Marianas. They match also the predictions based on independently the regression

small small islands off the east coast of Papua New Guinea was: species richness

derived derived for the well-studied islands in the Marianas [species richness

relationship relationship match closely the richnesses species that have been observed in the

0.5l(island 0.5l(island

size and and diversity. ecological size Extinctions have undoubtedly occurred in the Mar­

among among the Mariana islands.

of of the origins of several widespread species and the mode of dispersal to and

ianas ianas and our incomplete knowledge of these events obscure our understanding

man, man, perhaps in prehistoric times. However, this is unlikely to be the case with

endemics) endemics) were introduced by man, distributional patterns would not support

species might might species have been introduced prehistorically.

biogeographic biogeographic inferences except for subsequent extinctions influenced by island that that all reptiles and amphibians on very remote islands have been introduced by

in the the in Marianas within historical times. Crombie

section). section). the island endemics, endemics, island the to exists and determine at present way nonendemic which no

reflects reflects an equilibrium condition than does the total current species richness

species species were used. We assumed that the number of native species more likely

Pagan, Agrihan, Pagan, Agrihan, and Maug). In this second data analysis, only sufficiency native

(evidence (evidence for instability due to recent species introductions given is in the next

Papua Papua New Guinea. Second, executed we a similar analysis for the well-studied

the the sizes corresponding to those of the less-studied islands (Anatahan, Sarigan

we computed we computed the species richness values that would be expected for islands of

and and Guguan). From the regression oflog

islands of the the Marianas of islands chain (Guam, Rota, Tinian, Asuncion, Alamagan, Saipan,

with with the number of species to be expected on each island based on the species­

compared compared the observed number of all terrestrial herptile species on each island

be be used to estimate undersampling of species richness in two ways. First, we

of of sampling adequacy. area area relationship derived by Heatwole (1975) for small islands off the coast of

proximity proximity to source islands, they have been excluded from the analysis following

distance distance from source area. Because Cocos and Aguijan are anomalous in their

stantially stantially richer in This species. may account for the statistical insignificance of

Marianas Marianas are at least tens of kilometers distant from another island that is sub­

Marianas; Marianas; and with the exception of the islands Cocos and Aguijan, all of the

species diversity diversity (R species

( 197 5), 5), we found 197 that ( only island area contributed significantly to explaining

nearest nearest larger island (an estimate of colonization opportunities). Like Heatwole

to to the islands Heatwole considered, habitat diversity is relatively uniform in the

200 200 in in meters (a measure of habitat diversity), and reciprocal of the distance to the

the fraction of introduced species in his study area was relatively insignificant. insignificant. relatively was area study his in species introduced of fraction the

alterations by man (some historians estimate a pre-Magellan population of over over of population pre-Magellan a estimate historians (some man by alterations

to recent extinctions, or a prehistoric reduction in species due to intensive habitat habitat intensive to due species in reduction prehistoric a or extinctions, recent to species). Heatwole did not distinguish between native and introduced species as as species introduced and native between distinguish not did Heatwole species).

number and the total number of species on Guam (i.e., including introduced introduced including (i.e., Guam on species of number total the and number

the indigenous species, a good match exists between Heatwole's expected species species expected Heatwole's between exists match good a species, indigenous the

depauperate because it is the largest island in the group, so no larger nearby island island nearby larger no so group, the in island largest is the it because depauperate

the number of extant native species. Perhaps Guam has always been relatively relatively been always has Guam Perhaps species. native extant of number the

persal). Guam's low species richness may also indicate inadequate sampling prior prior sampling inadequate indicate also may richness species low Guam's persal).

sMns 170k t te ot, ieto iaporae o ntrl af dis­ waif natural for inappropriate direction a south, the to km 1,720 Manus, is

could act as a source for additional species (the nearest island larger than Guam Guam than larger island nearest (the species additional for source a as act could

for small islands that are very distant from a source area (MacArthur & Wilson Wilson & (MacArthur area source a from distant very are that islands small for

the well-studied islands of the Marianas is consistent with expectations of theory theory of expectations with consistent is Marianas the of islands well-studied the

2). For Guam, Heatwole's regression predicts a number substantially greater than than greater substantially number a predicts regression Heatwole's Guam, For 2).

species richness predictions, with Guam showing the greatest discrepancy (Table (Table discrepancy greatest the showing Guam with predictions, richness species

100,000 people on this 54, 100-ha island). Contrasting the poor fit obtained using using obtained fit poor the Contrasting 54, island). 100-ha this on people 100,000

1967). Despite the difference in exponent, the two regressions give nearly identical identical nearly give regressions two the exponent, in difference the 1967). Despite

V) V)

Q. Q.

a, a,

u u

VI VI

a, a,

20 20

10 10

15 15

4 4

5 5

3 3

2 2

100 100

Figure I. Relationship between island area and species richness for the native rep­ native the for richness species and area island between Relationship I. Figure

well-studied island (solid (solid dots) island well-studied

tiles and amphibians of the Mariana Islands. Regression line is fitted to the the to fitted is line Regression Islands. Mariana the of amphibians and tiles

fall below the regression line regression the below fall

0 0

500 1000 5000 1QOOO 1QOOO 5000 1000 500

Rodda Rodda

0 0

et et

Island area (ha) (ha) area Island

al

.: .:

Marianas Marianas Reptile Distribution

. .

See Table 2 for specific island values. values. specific island for 2 Table See

. .

Note that the less-studied islands (open circles) circles) (open islands less-studied the that Note

0 0

50,000 50,000 201 201 s

Table 2. Adequacy of sampling based on island size and two regressions relating species richness to island size. Species totals are for terrestrial species only. Within categories, islands are listed from south to north.

Sp. present Area Heatwole This study's Other native spp. likely to be Island (ha) prediction All Native prediction found

Well studied Guam 54,100 19.6 19 II 12.4 3: Rota 8,520 10.6 14 IO 8.6 ;:;· Tinian 10,180 11.2 14 9 8.9 a= Saipan 12,290 12.0 17 9 9.2 "!!?. Guguan 420 3.9 4 4 4.7 £ N Alamagan 1,130 5.4 9 7 5.7 ~ Asuncion 730 4.6 5 5 5.3 ::-N :0 Poorly studied ~ E. s/evini, L. lugubris, G. Anatahan• 3,230 7.6 4 3 7.1 oceanica, G. muti/ata Sarigan 500 4.1 5 4 4.9 L. lugubris C. poeci/op/eurus,E. s/evini, G. Pagan• 4,830 8.7 7 4 7.7 oceanica Agrihan 4,740 8.7 7 5 7.6 G. oceanica, E. s/evini E. caeruleocauda,L. lugubris, G. Maug 210 3.1 1 1 4.1 oceanica

*These islands have undergone severe recent volcanism and may not have the full complement of species that would be expected.

it will reach the other southern Marianas. Marianas. southern other the reach will it

ported to other islands (Fritts 1987, 1988; 1988; 1987, McCoid (Fritts islands other to ported

where it was accidentally introduced shortly after World War II (Savidge 1987, 1987, (Savidge II War World after shortly introduced accidentally was it where

after a single individual floated to an island on debris set loose during typhoons. typhoons. loose during set debris on island an to floated single a individual after

others. others.

Fritts 1988, Rodda et al. 1992). However, records of it being accidentally trans­ accidentally being it of records 1992). However, al. et 1988, Rodda Fritts

places to which humans have inadvertently transported it (McDowell 1974). 1974). (McDowell it transported inadvertently have humans which to places

parthenogenetic (McDowell 1974, Nussbaum 1980) 1980) 1974, (McDowell parthenogenetic it could Nussbaum readily establish itself

impossible to distinguish the area where it originated from the numerous similar similar numerous the from originated it where area the distinguish to impossible

in the Marianas (in Paris Museum by early 1840s, 1840s, by early Museum Paris (in 1917). Marianas see in the Van Denburgh Being

It It

Despite its cryptic habits, habits, cryptic its Despite freshwater streams or ponds. ponds. or streams freshwater

(Ernst (Ernst

from man, it could spread to other islands, such as Tinian, that have adequate adequate have that Tinian, as such islands, other to spread could it man, from

virtually all all of widest areas virtually has world, range reptile the warm of the any terrestrial

Marianas by the prehistoric settlers (Brown 1956). At present, however, it is is it however, present, At 1956). (Brown settlers prehistoric the by Marianas

ably nesting on the limited numbers of suitable beaches. No terrestrial or aquatic aquatic or terrestrial No beaches. suitable of numbers limited the on ably nesting

has apparently become established on Guam and probably Saipan. With help help With Saipan. probably and Guam on established become apparently has

turtles are native, although although native, turtles are

although there is the sound record for Saipan; and the frog's preferred habitat habitat preferred frog's the and Saipan; for record sound the is there although

from Australia in 1968 (Eldredge 1988). To date, it has not spread beyond Guam Guam beyond spread 1968 not has 1988). it (Eldredge in date, Australia To from

(marshes and drainage ditches) is relatively abundant on Tinian and Saipan. Saipan. and Tinian on abundant relatively is ditches) drainage and (marshes

of the other islands as it has done throughout the world. world. the throughout done has it as islands other the of

Marianas during the Japanese period. period. Japanese the during Marianas

control in 1937 (Anon. 1940, Eldredge 1988) and to the other large islands of the the of large islands other the 1940, 1988) 1937 to Eldredge (Anon. and in control

to tropical areas throughout the world, was released on Guam for garden slug slug garden for Guam on released was world, the throughout areas tropical to

Marianas. The gigantic poisonous toad toad gigantic The poisonous Marianas.

not normally native to oceanic islands. Two species have been introduced to the the to introduced been species have Two islands. oceanic to native normally not

between the number now known and the number expected on the basis of island island of basis the on expected number the and known now number the between

ber of expected additional species was based on the approximate discrepancy discrepancy approximate the on based was species additional expected of ber

ecological generalities developed in the final section of this paper. paper. this of section final the in ecological developed generalities

be discovered with additional collecting on the poorly sampled islands. The num­ The islands. sampled collecting poorly the on with additional be discovered

size. The predicted species were selected on the basis of the biogeographic and and biogeographic the of basis the on selected were species predicted The size.

is known from every well-studied island and probably occurs on most of the the of most on occurs probably and island well-studied every from known is

The Brown Tree Snake, Snake, Tree Brown The

The worm-like snake snake worm-like The

Sea turtles were once common around the Marianas (Pritchard 1981 1981 (Pritchard ), prob­ Marianas the around were common once Sea turtles

Litoria fa/lax, fa/lax, Litoria

Amphibians do not tolerate long exposure to salt water and therefore are are therefore and water salt to exposure long tolerate not do Amphibians

The right-hand column in Table 2 lists species that we judge most likely to to likely most we judge that species lists 2 Table in column right-hand The

& &

Barbour 1989). Some herpetologists assume that it was brought to the the to brought was it that assume 1989). herpetologists Some Barbour

a small green treefrog, was accidentally introduced to Guam Guam to introduced accidentally was treefrog, green small a

Interpretation Interpretation Distributional of Patterns

Rodda Rodda

R. braminus braminus R.

Trachemys script script Trachemys a,

Ramphotyphlops braminus, braminus, Ramphotyphlops

Boiga irregularis, irregularis, Boiga

et al.: et al.:

INTRODUCED SPECIES SPECIES INTRODUCED

Marianas Reptile Distribution Distribution Reptile Marianas

It It

was among the first first collected be was to the reptiles among

Bufo marinus, marinus, Bufo

will probably eventually spread to many many to spread eventually will probably

the common turtle of of turtle trade, the pet common the

is at present confined to Guam, Guam, to confined present at is

& &

Stinson 1991) 1991) suggest that Stinson

which has been introduced introduced been has which

transported with soil to to soil with transported 203 203

is is

= =

( (

Cryp­

Varanus Varanus

the the gecko indi­

H. H. javanicus

E. E. caeruleocauda,

of of

Lampro/epis Lampro/epis smar­

from several islands. islands. from several

and and

90% 90%

Car/ia. Car/ia. A. caro/inensis

has has become established only

Fritts Fritts unpub. data) and it is

E. E. slevini

& &

Fritts Fritts unpub. data). The lizard's

and and

& &

has has become conspicuous and wide­

arrived arrived more recently and is still rare

constitutes constitutes over

An An extremely lizard, aggressive it readily

Ano/is Ano/is carolinensis

Car/ia Car/ia

Ano/is Ano/is

fusca. fusca.

frenatus frenatus

Micronesica Micronesica 24(2), 1991

C. C.

may may also affect the numbers of

was was introduced to southern Marianas in the 1960s.

a a widespread human comensal, is thought most by,

H. H.

Lampro/epis Lampro/epis smaragdina

may may have played a role in the disappearance of

Car/ia Car/ia

fusca fusca

C. C.

Car/ia fusca fusca Car/ia

does not not does This limitation from occur houses away (McCoy 1980). does

from from the Marianas, probably Guam. This would make it among the

have have expanded their ranges more slowly than

is is thought to have been introduced there, as it has been throughout the

on on the other Marianas. Its dispersal to islands new in the Marianas is not

The large green skink skink green The large

The other other The introduced two lizards,

The The skink

Hemidactylus Hemidactylus Jrenatus,

On On the basis implausibility of natural of dispersal to the Marianas,

on on Saipan and Tinian. It is locally abundant on large trunks and in the open

impeded impeded by competition from other lizards, as the Marianas have no native,

ian. ian. The California Academy of Sciences has a single specimen from Tinian,

tions tions to Tinian are likely, and the habitat appears similar to that occupied by

diurnal diurnal lizards found primarily in foliage.

intensive intensive searches (see also Wiles et al. Additional 1989). inadvertent introduc­

snake. snake. On the other major islands,

(Greg (Greg Mayer, pers. comm.), but none was evident on the island during recent

Ano/is Ano/is numbers numbers appear to have subsequently declined in areas heavily populated by the

away from from human away settlements. It apparently has not become established on Tin­

the the introduced Brown Tree Snake (Smith

places where where places water is regularly available. It spread rapidly after its introduction

an arboreal, diurnal diurnal arboreal, an insectivore around that well does human habitations other or

agdina, agdina,

to to Guam in the mid-1950s (Eldredge but 1988), it is a preferred prey item for

1990). Because it it is colonist, an it Because aggressive probably will spread 1990). throughout the

completed. completed.

spread spread on Cocos; but studies on the impact of this expansion have not been

Where Where they coexist,

tob/epharus poeci/op/eurus, poeci/op/eurus, Emoia tob/epharus atrocostata,

especially especially on the ground. Recently,

takes takes food from other small terrestrial, diurnal lizards. It does especially well

as as beach strand.

species. species. The Marianas form will probably be given a new name; for the time

along along roadsides or in suburban lawns but will also invade other habitats, such

G. Ingram (in litt.) suggests that that many the Ingram G. litt.) of (in complex suggests a nominal similar is species

being we will continue continue will being we to use

Marianas. Marianas.

not not hold for the Marianas;

widespread in disturbed in disturbed widespread but on Tinian vegetated sites and et al. 1989, Rota (Wiles

first first reptiles collected in the Marianas. On most Pacific islands where it occurs,

viduals viduals in many forested areas of Guam (Rodda

H. frenatus frenatus H.

the the chain for at least 150 years. Fitzinger 1843) reported ( a

Pacific (Brown (Brown It Pacific 1956). has been seen on every well-studied island the of chain

herpetologists herpetologists to have been introduced to the Marianas, although it has been in

indicus indicus

and and may be expected to have reached the others.

204 204 Jrenatus) Jrenatus)

the chain to the other, but may be missing on particular islands. For example, example, For islands. particular on missing be may but other, the to chain the

Boiga irregu/aris, Varanus indicus, Lampro/epis smaragdina, Rattus Rattus smaragdina, Lampro/epis indicus, Varanus irregu/aris, Boiga by the species-area relationship (Fig. 1). All five species occur from one end of of end one from occur species five 1). All (Fig. relationship species-area the by

apparently too small to support the full complement of of lizards, full as the small native suggested support to complement too apparently

in clearings, around abandoned buildings, on the forest floor, and in trees. Thus, Thus, trees. in floor, forest and the on buildings, abandoned clearings, around in

direct behavioral interference as applies to the food thefts by the large large aggressive the by thefts food the to applies as interference behavioral direct of the other skinks skinks except of other the

intensively with any other single single species. other any with intensively found on nearly all islands in the Marianas. Some of the northern islands are are islands northern the of Some Marianas. the in islands all nearly on found

it does not appear to be a habitat specialist and would not be likely to compete compete likely to be not would and specialist habitat a be to appear not does it

shrew shrew

caused habitat disruption. Being endemic, it must have been present in the chain chain the in present been have must Being it endemic, disruption. habitat caused

logically displaced by them, its large size would argue against a mechanism of of mechanism a against argue would size large its them, by logically displaced

man. man.

more recent arrivals even before the disturbances and introductions brought by by brought introductions and disturbances the before even arrivals recent more

erd rmGa, oa ad iin nhsoi times historic in Tinian and Rota, Guam, from peared

for an evolutionarily long time and may have been ecologically supplanted by by ecologically supplanted been have may and time long evolutionarily an for Carlia Carlia

distribution, although it may also indicate inadequate sampling prior to human­ to prior sampling inadequate indicate also may it although distribution,

ulations are known only from the far northern islands Asuncion and Alamagan. Alamagan. and Asuncion islands northern far the from only known are ulations

pro/epis pro/epis

of of

It It

island: island:

3). 3).

uation of human alterations to the environment, an equilibrium condition is not not is condition equilibrium an environment, the to alterations human of uation

exotics as well as the greatest loss of native species. Given the probable contin­ probable the species. Given native of loss greatest the well as as exotics

Table 3. The most affected island is Guam, which hosts the largest number of of number largest the hosts which Guam, is island affected most The 3. Table

tion of population decreases and range reductions among native species listed in in species listed native among reductions range decreases and population of tion

likely to be reestablished in the foreseeable future. future. foreseeable the in reestablished be likely to

idodactylus lugubris, Gehyra mutilata, mutilata, Gehyra lugubris, idodactylus

species does not appear to be an aggressive aggressive colonizer. an be to appear not does species

trunks, especially those with loose bark). Food and available habitat for for habitat available and Food bark). loose with those especially trunks,

has destabilized the resident herpetological communities. Note the large large propor­ the Note communities. herpetological resident the destabilized has

trunks, a habitat not used to any great extent by native skinks skinks native by extent great any to used not habitat a trunks,

dation by by dation

t o aglo um n h 16sfie Edeg 98,pras u t pre­ to due 1988), perhaps (Eldredge 1960s failed the in Guam Mangilao, to it

but it will occupy large trees in forested areas as well. An attempt to introduce introduce to attempt An well. as areas forested in trees large occupy will it but

crowns crowns of trees, especially trees are a areas. preferred habitat, in Ornamental urban uses such a habitat a little, and the crepuscular crepuscular the and little, a habitat uses a such

is present but not common on Cocos. This spotty pattern suggests suggests relictual a pattern spotty This Cocos. on common not but present is

E. slevini, slevini, E.

E. slevini slevini E.

In contrast to to contrast In

Of the 11 native lizards, six have been found on almost every well-studied well-studied every almost on found been have six lizards, 11 native the Of

The introduction to the Marianas of9-l l species ofreptiles and amphibians amphibians and species ofreptiles l of9-l Marianas the to introduction The

E. slevini slevini E.

Suncus murinus. murinus. Suncus

in encounters with the smaller smaller the with encounters in

Cryptoblepharus poeci/op/eurus, Emoia caeru/eocauda, Emoia s/evini, Lep­ s/evini, Emoia caeru/eocauda, Emoia Cryptoblepharus poeci/op/eurus,

exist throughout the Marianas; but on the basis of its slow spread, the the spread, slow its of basis the on but Marianas; the throughout exist

Boiga. Lamprolepis Lamprolepis Boiga.

the only known Marianas endemic, all are widespread species species all widespread are endemic, (Table only Marianas known the

sas nmlu i ta i paety a eoerr r disap­ or rare become has apparently it that in anomalous also is

is larger than the other native skinks. skinks. native other the than larger is

E. slevini, slevini, E.

Rodda Rodda

E. atrocostata. atrocostata. E.

et et al

the other widespread native lizards are likely to be be likely to are lizards native widespread other the

shows a strong preference for large, exposed tree tree exposed large, for preference strong a shows

NATIVE SPECIES SPECIES NATIVE

.: .:

Marianas Reptile Distribution Distribution Reptile Marianas

E. caeruleocauda. caeruleocauda. E.

and and

It It

It It

may be vulnerable to exotic exotic may to predators: be vulnerable

Gehyra oceanica. oceanica. Gehyra

will overlap to some extent with all all with extent some to overlap will

Lipinia noctua noctua Lipinia

If If

We We found£ have

. .

tpeet es pop­ dense present, At

it has or is being eco­ being is or has it

With the exception exception the With

may use use large tree may

(Emoia slevini slevini (Emoia

sp., and the the and sp.,

. .

slevini slevini

Lam­

205 205 ' '

Varanus indicus indicus Varanus X X

Hemidactylus frenatus frenatus Hemidactylus X X X X

Carlia fusca fusca Carlia X X X X

Lamprolepis smaragdina smaragdina Lamprolepis X X X X X X

Ano/is carolinensis carolinensis Ano/is X X X X

Boiga irregularis irregularis Boiga X X X X

Trachemys scripta scripta Trachemys X X X X

Litoria fallax fallax Litoria X X

Bufo marinus marinus Bufo ? ? X X

~ ~

Ramphotyphlops braminus braminus Ramphotyphlops ? ? X X

~ ~

Gehyra oceanica oceanica Gehyra X X x(Guam) x(Guam) X X

::-

Gehyra mutilata mutilata Gehyra

X X x(Guam) x(Guam) X X

...., ....,

~ ~

Lepidodactylus lugubris lugubris Lepidodactylus X X X X ...., ....,

~- Emoia slevini slevini Emoia x (Guam, Rota, Tin.) Tin.) Rota, (Guam, x X X

Emoia caeruleocauda caeruleocauda Emoia n n

X X X X

::s ::s

a a

poecilopleurus poecilopleurus C. C. X X X X x(Guam) x(Guam) X X

n· n·

Perochirus ate/es ate/es Perochirus a: a: X X X X x (Guam, Tin., Sai.) Sai.) Tin., (Guam, x X X X X

Nactus pelagicus pelagicus Nactus X X X X x (Guam, Tinian) Tinian) (Guam, x X X X X

Emoia atrocostata atrocostata Emoia ? ? X X X X X X X X

Emoia cyanura cyanura Emoia X X X X X X X X

Lipinia noctua noctua Lipinia ? ? X X X X X X X X

Species Species Wide sp Wide . . range range a. spec Hab. . . ny aie eet pop Recent Native only . . decline or range contract. contract. range or decline

n ot Mar South In . .

was chosen to emphasize relationships between ecological and distribution variables (columns), with native species appearing in the first rows. rows. first the in appearing species native with (columns), variables distribution and ecological between relationships emphasize to chosen was

Table 3. Biogeographic and ecological attributes of Mariana Islands reptiles and amphibians (established terrestrial species only). Order of species species of Order only). species terrestrial (established amphibians and reptiles Islands Mariana of attributes ecological and Biogeographic 3. Table

°' °' ~ ~

arrivals or they did not attain reproductive isolation before before genetically isolation compatible reproductive attain not or they did arrivals

of these remote oceanic islands have either been supplanted by more recent recent more by supplanted been either have islands oceanic remote these of

in the Marianas suggests that most reptile populations that evolved in in evolved the isolation that suggests in the Marianas populations reptile most that

zone marked by the shrub shrub the by marked zone

disturbances (McCoy 1980). We have never found it inland from the salt spray spray salt the from inland it found never 1980). have We (McCoy disturbances

in the Marianas are ecologically specialized forms. forms. ecologically specialized are Marianas the in

despite having wide species ranges all five native lizards having limited ranges ranges limited having lizards native five all ranges species wide having despite

understood. In the Marianas, it has been found primarily in undisturbed forests, forests, undisturbed in primarily found been has it Marianas, the In understood.

is a specialist for rocky habitats. The habits of of habits The habitats. rocky for specialist a is

omons, it reportedly forages primarily in tide pools where where pools tide in forages primarily reportedly it omons,

fte ain rpie, sfud xlsvl ln ok hrlns I te Sol­ the In shorelines. rocky along exclusively found is reptiles, Mariana the of

logically logically broader pharus. pharus.

Lipinia Lipinia

mostly on large tree trunks (Saba (Saba Thus, forests. close to buildings 1981) on large trunks on tree mostly and th

never reached the northern Marianas. Marianas. northern the reached never

due to extirpation associated with small island area, rather than their having having their than rather area, island small with associated extirpation to due

Emoia cyanura, Emoia atrocostata, Nactus pelagicus, pelagicus, Nactus atrocostata, Emoia cyanura, Emoia for waif dispersal, and their absence from the smaller Mariana islands is is islands probably Mariana smaller the from absence their for waif and dispersal,

and occurs on the remote Marcus Island. These species well species probably These adapted are Island. Marcus remote the occurs on and

bution is is bution

taod te oetdznsfeune b h mrhlgcly iia bt eco­ but similar morphologically the by frequented zones forested the avoids It

specializes in hot, dry, open areas, especially those near the coast (McCoy 1980). 1980). (McCoy coast the near those especially areas, open dry, hot, specializes in

though these five lizards are specialized in their habits compared to the six six wide­ the to compared habits their in specialized are five lizards these though

fully resolved (Moritz 1987). One species that is arguably restricted in its distri­ its in restricted arguably is that species 1987). One (Moritz fully resolved

Marianas is part of a unisexual/bisexual species complex that has not yet been been yet not has that complex species unisexual/bisexual a of part is Marianas

cies. cies.

eod a edet roeu ietfctos fmrhlgcly iia spe­ similar morphologically of identifications erroneous to due be may records

spread species, they are not geographically restricted in their species species species, spread ranges in their geographically not (Table are they restricted

southern islands and none is known to occur on all four islands: islands: four all on occur to known is none and islands southern

in the Marianas, the other five native lizards are all restricted to the four large large four the to restricted all are lizards native five other the Marianas, the in

tree trunks and areas near shorelines. Guguan has extensive areas ofloose sandy sandy ofloose areas extensive has Guguan shorelines. near areas and trunks tree

skink, a role occupied by by occupied a role skink,

its missing congener. On Guguan, Guguan, On congener. missing its

oceanica oceanica

its niche to include the unoccupied space. For example, on Asuncion, Asuncion, on example, For space. unoccupied the include to niche its

the islands where a species is missing, a similar species appears to have expanded expanded have to species species appears a where similar a islands is missing, the

Guguan; but all species were historically present on the four large islands. On On islands. large four the on present historically were species all but Guguan;

soil throughout the island, a feature which may be advantageous to to advantageous be may which feature a island, the throughout soil

3). Most are found throughout the Pacific, although some of the distributional distributional the of some although Pacific, the throughout found are Most 3).

Cryptoblepharus Cryptoblepharus

Gehyra mutilata mutilata Gehyra

Unless most species arrived with humans, the paucity of reptile endemics endemics reptile of paucity the humans, with arrived species most Unless

The five geographically restricted species all have ecological ecological specializations. have species all five geographically restricted The

Although the six widespread native lizards are found on almost every island island every almost on found are lizards native six widespread the Although

E. cyanura cyanura E.

is the only diurnal, primarily arboreal species. species. arboreal primarily diurnal, only the is

is extremely abundant and occupies the surfaces normally inhabited by by inhabited normally surfaces the occupies and abundant extremely is

Perochirus ate/es, ate/es, Perochirus

is missing from Asuncion and and Asuncion is missing from

has been confused with with confused been has

and and

E. caeruleocauda. E. atrocostata, atrocostata, E. caeruleocauda. E.

E. caeruleocauda caeruleocauda E.

Rodda Rodda

E. caeruleocauda caeruleocauda E.

Pemphis acidulus. acidulus. Pemphis

yet it is widespread in the Carolines and Marshalls Marshalls and Carolines the in widespread is it yet

et et al.:

Marianas Reptile Distribution Distribution Reptile Marianas

Cryptoblepharus Cryptoblepharus

coexist, coexist,

E. impar impar E.

on the other islands. On islands where where islands On islands. other the on

In the Marianas, Marianas, the In

E. caeruleocauda caeruleocauda E.

Cryptoblepharus Cryptoblepharus

Perochirus ate/es ate/es Perochirus

and the the and

among the most specialized specialized most the among

is the ubiquitous ground ground ubiquitous the is

and and

it it

E. cyanura cyanura E.

Perochirus ate/es. ate/es. Perochirus

will will seek refuge from

Nactus Nactus

Nactus pelagicus pelagicus Nactus

does not inhabit inhabit not does

Lipinia noctua, noctua, Lipinia

specializes on on specializes

found in the the in found

are not well well not are

reportedly reportedly

Cryptoble­

Gehyra Gehyra

Al­ 207 207

the the Marianas are in

If If

is is found nowhere else but the nearby islands

Acknowledgments Acknowledgments

Micronesica Micronesica 24(2), 1991

Glass Glass 1991) and one additional species, the White-throated Ground

& &

(Ga/licolumba (Ga/licolumba xanthonura),

The The opportunity to visit the remote northern islands of the Marianas was

The The reptiles and amphibians of the Mariana Islands are all excellent dis­

ianas. ianas. We also wish to thank the numerous people who have collected specimens

extant extant island records for reptiles and amphibians in Oceania, including the Mar­

tional tional Museum of Natural History, who examined specimens and compiled the

visit visit to the Marianas. We are greatly indebted to Ron Crombie of the U.S. Na­

Aquatic Aquatic and Wildlife Resources provided irreplaceable assistance during every

of of the U.S.C.G.S. Cape George for their friendly support. Guam's Division of

of of the U.S. Coast Guard. We thank captain Dan Cristovich and the entire crew

provided provided by Arnold Palacios, Phil Glass, and others with the Division of Fish

and and Wildlife, Department of Natural Resources, CNMI and with the cooperation

species species and a higher proportion of ecologically specialized forms. Unfortunately,

tofaunas tofaunas associated with the introduction of exotic species.

Pacific Pacific islands should vary with distance from source areas, with only the most

these these more diverse islands have all experienced declines in their native herpe­

persers. persers. Proximity to source areas does not appear to influence their distribution,

some some sense more remote for birds than reptiles, this argument may help explain

netically netically disruptive influence of repeated immigration.

although although size of island does. The larger, southern islands of the chain have more

the the differences between bird and reptile endemism in these islands.

remote remote areas having sufficient isolation for speciation to occur without the ge­

accidentally accidentally washed to sea on debris. Diamond (1984) argued that endemism in

are are almost totally incapable of propelling themselves back to land if they are

ities ities to resist unintended transport and their more limited survival time when

Their Their are eggs resistant to damage by salt spray (Brown Alcala & and 1957), they

as as the Marianas. Geckos, in contrast, can survive long periods without food.

deprived deprived of food, may not be well suited for waif dispersal to remote islands such

relative relative to its occurrence in reptiles. Land birds, with their more developed abil­

indicates indicates that successful waif dispersal of non-migratory island land birds is rare

us us to consider the other possibility: perhaps the high endemism of Marianas birds

Dove Dove

(Reichel (Reichel

with with oceanic island land birds (Brockie et al. 1988). Furthermore, it encourages

hypothesis, hypothesis, course; of but consistent it is with the general characteristics associated

logical logical displacement. This analysis is not a strong test of the competitiveness

become become established on many islands of the Marianas during the last few decades

of of Yap (Pratt et al. 1987). The ease with which introduced bird species have

in in the Marianas. Of the 21 breeding land birds of the Marianas, nine are endemics

mobile mobile birds have shown a much greater tendency to remain isolated and speciate

individuals individuals arrived to swamp the emerging local adaptations. This pattern con­

gives gives no indication that the resident bird species are especially resistant to eco­

trasts trasts strikingly with that of the Marianas' native birds. Paradoxically, the more 208 208 Rodda et al.: Marianas Reptile Distribution 209 or accompanied us in the field in the Marianas. 0. E. Maughan, K. J.Cook, and M. J. McCoid suggested many improvements to the manuscript.

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287029-33 287029-33

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APPENDIX APPENDIX

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Boiga Boiga irregularis,

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(Alam), (Alam),

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287197-215 287197-215

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287227 287227

(Agui), (Agui),

287034 287034

287051-8 287051-8

287070-94 287070-94

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301890 301890

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287059-68 287059-68

301893 301893

287069 287069

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Apr. Apr.

J. J.

not not cat. (Guam)

287175-95 287175-95

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9 9

287235-6 287235-6

C. C.

284622 284622

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mutilata: mutilata:

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poecilopleurus: poecilopleurus:

/ugub: /ugub:

frenatus: frenatus:

fusca: fusca:

C. C.

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Island names names Island

L. L.

L. L. noctua.

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H. H.

R. R. braminus:

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