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31 August 2019 Population Density of a Clonal Gecko Species in Its Northernmost Range, the Ryukyus in Japan
Osamu Sakai
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Many species of organisms are known to have expanded their distributional ranges and established highly dense populations in their nonnative areas due to human activities. Several gecko species have been introduced from tropics to seasonal subtropics with the aid of artificial transportations. However, it has not yet been well-documented as to whether invasive tropical geckos flourish in extra-tropical cooler areas outside their native range. Here, I report demographic information of the mourning gecko, Lepidodactylus lugubris, in its northernmost distribution, the Ryukyu Archipelago in Japan. I conducted a mark-recapture survey of mourning geckos inhabiting a coastal vegetation habitat and estimated their population size using the Jolly-Seber open population model. An estimated 94–284 individuals lived in a small beachfront forest. The population showed a high density (880–2,656 geckos/ha), which is comparable to that of other invasive gecko populations in tropical areas. The results imply a successful colonization of clonal geckos at their northernmost invasion front.


Many animal species are introduced outside their native range because of intentional or accidental artificial transportations by humans (Sakai et al., 2001; Parker et al., 2013). In some cases, invasive reptiles and amphibians flourish in non-native ranges, causing serious impacts on local ecosystems (Bomford et al., 2009; Kraus, 2009). Several gecko species frequently invade new areas in association with human activities and colonize both urban and natural habitats (Rödder et al., 2008; Rödder and Lötters, 2009; Hoskin, 2011). For example, the Mediterranean house gecko, Hemidactylus turcicus, invaded the United States where it has established dense populations in Florida (479–1,476 geckos/ha; Punzo, 2001) and in Oklahoma (478 geckos/ha; Locey and Stone, 2006). In the case of H. turcicus, its climatic environments are similar between the native and non-native temperate zones (Rödder and Lötters, 2009; but see Wessels et al., 2018). In other cases, invasions are also observed across different climatic environments (e.g., from wet tropics to seasonal subtropics). However, it remains unclear whether introduced geckos from tropics can flourish in non-native, cooler, subtropical areas.

The mourning gecko, Lepidodactylus lugubris (Duméril and Bibron, 1836), is one of the most widely distributed terrestrial reptile species, commonly occurring on most tropical and subtropical Pacific and Indian Ocean islands (Ineich, 1999). The success of L. lugubris is partially due to parthenogenetic reproduction: an all-female population produces clones (genetically uniform individuals) without mating. Because parthenogenetic reproduction allows establishment of a sustainable population from only a single individual, L. lugubris is a successful colonizer, particularly in island ecosystems where competition is reduced and food is abundant (Ineich, 2010). The geographical origin of unisexual L. lugubris is assumed to be tropical islands in Micronesia (Radtkey et al., 1995). In addition, further clonal diversity has been generated in other areas, and several endemic clonal types are reported in small isolated islands (e.g., the Daito Islands, Japan: Yamashiro et al., 2000; Murakami and Hayashi, 2019). Recently, several additional populations have been introduced and established in South and Central America, Australia, and Asia (Bauer and Henle, 1994; Hoogmoed and Avila-Pires, 2015; Lapwong and Juthong, 2018).

The Ryukyu Archipelago of Japan represents the northernmost distributional range of L. lugubris, where the species experiences a cold winter season compared to the tropics (Ota, 1994; Ineich, 1999; Sakai, 2016). In this area, populations of L. lugubris are divided into two groups based on their different ende-micity and occurrence. In the Daito Islands, populations consist of several clones endemic to this isolated island group (Yamashiro et al., 2000; Murakami and Hayashi, 2019). They are considered to be native in these small islands, and their occurrence there was already recognized by the mid-1930s (Okada, 1936; Ota and Toyama, 1992). In other island groups in the Ryukyu Archipelago, L. lugubris was first recorded in the early 1970s and has been reported from most islands belonging to Okinawa Prefecture since then (Shibata et al., 1972; Maenosono and Toda, 2007). These non-Daito Ryukyu populations, reportedly predominated by the widely distributed triploid Clone C, are considered to have originated from recent accidental artificial transportations (Ota et al., 2004). In spite of several distributional reports of L. lugubris in the Ryukyu Archipelago, there is no demographic information of the invasive populations. During an ecological survey of L. lugubris on Okinawa-jima Island, I found a dense population in a coastal vegetation habitat where I conducted a mark-recapture survey and estimated their population density.

Materials and Methods

Field survey

I conducted a field survey at a small, elongated beachfront forest (100 m length, 6–11 m width, 1,068 m2 area) on Okinawa-jima Island, Japan (26°44′34″N, 128°10′31″E) (see figure in Sakai, 2019). This forest mainly consists of sea hibiscus (Hibiscus tiliaceus: 8 m mean height), tropical almond (Terminalia catappa: 11 m mean height), screw pine (Pandanus odorifer: 8 m mean height), and beach cabbage (Scaevola taccada: 1 m mean height). The forest boundaries faced two types of environments: a beach 60–80 m width from the shore line, and a town area where pedestrians and cars pass both day and night. The nearlest street lamps were located over 50 m away and the study area had less than 3 lx of ambient light at night.

A total of four mark-recapture surveys were conducted over three years (September 2013, June and September 2014, and September 2015). In each survey period, I usually conducted five to six sampling efforts at three-day intervals. However, I sometimes conducted sampling efforts for two consecutive days while keeping previously collected geckos in captivity (28% of all sampling efforts), which I refer to as “consecutive samples” in the following analysis. I found three gecko species (Lepidodactylus lugubris, Gekko hokouensis, and Hemidactylus frenatus) in the habitat but collected only L. lugubris during the field survey. In each sampling day, I searched for geckos from sunset to midnight (for approximately five hours) by walking along the outer edge of the forest. I collected geckos by hand and placed them in small Ziploc bags (10×7 cm), that were punctured with several small holes to allow air exchange. I immediately transported geckos to an indoor field-laboratory close to the field site (<1 km). In the day following capture, I measured their snout-vent length and weighed them. I marked them with a toe clipping method and then photographed each gecko for complementary individual identification. After the measurements and manipulations, each gecko was released at its precise capture point.

Population analysis

I applied capture and recapture data to the Jolly-Seber open population model (White and Burnham, 1999). I used the formulation POPAN of the software MARK Version 8.0. The formulation POPAN allows the estimation of four demographic parameters: apparent survival rate (Phi), capture rate (P), probability of entrance (Pent), and population size (N). Considering numerical features of these demographic parameters, the following link functions were used in all models: logit for Phi and P, multinominal logit for Pent, and identity for N (see details in White and Burnham, 1999). The parameter Pent was considered to be time dependent (given parameter was changing during a survey period). On the other hand, the parameters Phi and P were considered as either time dependent or constant (given parameters were stable during a survey period). Therefore, I built four models with different combinations of demographic parameters (time dependent or constant) and selected the best ones in each survey period. Model selection was carried out based on the lowest Akaike Information Criterion corrected for small samples (AICc).

Time intervals between separate sampling efforts were set on a daily basis. In the case of consecutive samples, I started the next sampling effort while keeping previously collected geckos in captivity. Such consecutive samples were pooled as “one sampling occasion” that was regarded to be conducted on the intermediate day (Schwarz and Arnason, 2009). For example, if I conducted sampling efforts on days 3, 4, and 9, I pooled days 3 and 4 as one sampling event that was conducted on day 3.5 (intermediate between days 3 and 4). Then, I calculated the time interval between separate sampling efforts as 5.5 days (the interval between days 3.5 and 9).


I collected 369 individuals in a total of 626 captures during four survey periods (the number of captures: 223 in September 2013 [6 sampling days], 91 in June 2014 [5 sampling days], 156 in September 2014 [5 sampling days], and 156 in September 2015 [6 sampling days]). Out of these 369 geckos, 131 individuals (35.5%) were captured multiple times; the mean number of captures per individual was 1.70±1.17 (1–10) (mean±SD, range). The mean time interval between capture and recapture was 6.9±4.4 (4–23) days within each survey period (n=207) and 278.5±129.7 (71–477) days across survey periods (n=50).

The best models had different combinations of demographic parameters among survey periods (Table 1). In September 2013 and June 2014, the models with constant survival rate (Phi) and constant capture rate (P) showed the lowest AICc. On the other hand, in September 2014 and September 2015, the models with constant survival rate (Phi) and time dependent capture rate (P) showed the lowest AICc. According to the best models in each survey period, total population size was estimated as 94–284 individuals (Table 2). Given that the beachfront forest is approximately 1,068 m2, the density of the focal population was calculated as 880–2,656 geckos/ha (i.e., 0.09–0.27 geckos/m2).

Table 1.

Results of model selection in population analyses. Models with different combinations of demographic parameters (Phi: apparent survival rate, P: capture rate, Pent: probability of entrance) were compared by AICc. Parameters Phi and P were considered as either time dependent (changing during a survey period) or constant (stable during a survey period). “t” indicates time dependent parameters, and “c” indicates constant parameters.


Table 2.

Population size and density of mourning geckos. Population size was estimated by the best models in each survey period (see details in Table 1). Population density was calculated as the number of individuals divided by the field area (1,068 m2).



The population analysis demonstrates that L. lugubris established a dense population on subtropical Okinawa-jima Island. Conspecifics in tropical areas show population densities of 8,600 geckos/ha in Oahu, Hawaii (Jarecki and Lazell, 1987), 7,600 geckos/ha in Moorea, French Polynesia (Ineich, 1988), and 1,000–2,700 geckos/ha in Suva, Fiji (Case et al., 1994). Another invasive gecko species, Hemidactylus frenatus, established a dense population of 1,000–3,000 geckos/ha in Suva, Fiji (Case et al., 1994). It should be noted that these population densities were estimated by different survey efforts and methods. However, the density of the focal subtropical population of L. lugubris seems to be as high as that of many tropical populations. This result implies a successful colonization of invasive L. lugubris in a cooler non-native subtropical area.

However, considering spatial ecological features of L. lugubris, the population size of the present survey may possibly be underestimated. Mourning geckos in the focal population show a high level of site fidelity and a small home range (Sakai, 2019). If some geckos inhabit areas where they are difficult to be captured (e.g., dense bushes or high perch site), sampling would be biased to individuals inhabiting areas where they are easily captured. In this case, the survey area is only a part of the actual occupied area by the geckos. It should be noted that the Jolly-Seber open population model assumes no sampling bias between marked and unmarked individuals (Pledger and Efford, 1998). Given that unidentified individuals of L. lugubris were also observed in areas where they were impossible to capture, it is most likely that the actual population size of L. lugubris could be much larger than the present estimation.

In conclusion, this study shows that L. lugubris flourishes at the northernmost extremity of its range at similar densities as those observed in tropical populations. This is the first report that quantifies the population density of a tropical gecko species that invaded the seasonal subtropics. Further demographic investigation in other non-native populations, as well as native Daito populations, of L. lugubris would help to understand why and how highly dense clonal populations occur in cooler areas. In addition, the occurrence of dense populations of a non-native predator may impact potential prey species, such as native small insects, and create competition with native insectivorous lizards. However, the potential threat of L. lugubris to local ecosystem is still unclear in the Ryukyu Archipelago. In the future, comparative ecological surveys between areas with and without invasive L. lugubris would be informative.


I am grateful to A. Mori for reviewing the manuscript and providing accommodation near the field site. I also express my appreciation to I. Ineich and an anonymous reviewer for providing insightful comments and to R. Noelikanto for translating French language documents. The present study was carried out in compliance with the guideline of the Animal Care and Use Committee of Kyoto University. The field survey was conducted under the permission of the Department of Agriculture, Forestry and Fisheries of Okinawa Prefecture. The sampling procedures were designed to minimize stress and harm to the subjects.

Literature Cited


Bauer, A. M. and Henle, K. 1994. Gekkonidae (Reptilia, Sauria). Part 1: Australia and Oceania. Das Tierreich 109 . Walter de Gruyter, Berlin. Google Scholar


Bomford, M., Kraus, F., Barry, S. C., and Lawrence, E. 2009. Predicting establishment success for alien reptiles and amphibians: A role for climate matching. Biological Invasions 11: 713–724. Google Scholar


Case, T. J., Bolger, D. T., and Petren, K. 1994. Invasions and competitive displacement among house geckos in the tropical Pacific. Ecology 75: 464–477. Google Scholar


Hoogmoed, M. S. and Avila-Pires, T. C. 2015. Lepidodactylus lugubris (Duméril & Bibron 1836) (Reptilia: Gekkonidae), an introduced lizard new for Brazil, with remarks on and correction of its distribution in the New World. Zootaxa 4000: 90–110. Google Scholar


Hoskin, C. J. 2011. The invasion and potential impact of the Asian house gecko (Hemidactylus frenatus) in Australia. Austral Ecology 36: 240–251. Google Scholar


Ineich, I. 1988. Estimation expérimentale de la densité d'une population anthropophile de Lepidodactylus lugubris (Sauria: Gekkonidae) sur l'île de Moorea, Polynésie française. Bulletin de la Société Herpétologique de France 48: 22–29. Google Scholar


Ineich, I. 1999. Spatio-temporal analysis of the unisexual-bisexual Lepidodactylus lugubris complex (Reptilia, Gekkonidae). p. 199–228. In: H. Ota (ed.), Tropical Island Herpetofauna: Origin, Current Diversity, and Conservation. Elsevier Science, Amsterdam. Google Scholar


Ineich, I. 2010. How habitat disturbance benefits geckos: Conservation implications. Comptes Rendus - Biolgies 333: 76–82. Google Scholar


Jarecki, L. and Lazell, J. D. 1987. Zur Grösse und Dichte einer Population von Lepidodactylus lugubris (Duméril & Bibron, 1836) in Aiea, Hawaii (Sauria: Gekkonidae). Salamandra 23: 176–178. Google Scholar


Kraus, F. 2009. Alien Reptiles and Amphibians: A Scientific Compendium and Analysis. Springer Science & Business Media B. V., Dor-drecht. Google Scholar


Lapwong, Y. and Juthong, W. 2018. New records of Lepidodactylus lugubris (Duméril and Bibron, 1836) (Squamata, Gekkonidae) from Thailand and a brief revision of its clonal composition in southeast Asia. Current Herpetology 37: 143–150. Google Scholar


Locey, K. J. and Stone, P. A. 2006. Factors affecting range expansion in the introduced Mediterranean gecko, Hemidactylus turcicus. Journal of Herpetology 40: 526–530. Google Scholar


Maenosono, T. and Toda, M. 2007. Distributions of amphibians and terrestrial reptiles in the Ryukyu Archipelago: A review of published records. Akamata (18): 28–46. Google Scholar


Murakami, Y. and Hayashi, F. 2019. Molecular discrimination and phylogeographic patterns of clones of the parthenogenetic gecko Lepidodactylus lugubris in the Japanese Archipelago. Population Ecology 61: 315–324. Google Scholar


Okada, Y. 1936. Studies of the lizards of Japan 1. Gekkonidae. Science Report in Tokyo Bunrika Daigaku 2: 233–289. Google Scholar


Ota, H. 1994. Female reproductive cycles in the northernmost populations of the two gekkonid lizards, Hemidactylus frenatus and Lepidodactylus lugubris. Ecological Research 9: 121–130. Google Scholar


Ota, H., Toda, M., Masunaga, G., Kikukawa, A., and Toda, M. 2004. Feral populations of amphibians and reptiles in the Ryukyu Archipelago, Japan. Global Environmental Research 8: 133–143. Google Scholar


Ota, H. and Toyama, M. 1992. Reptiles and amphibians of Minami- and Kita-Daitojima Islands of the Ryukyu Archipelago, Japan. p. 63–72. In: M. Nishihara (ed.), Daito Flying Fox. Survey Reports on Natural Monuments of Okinawa Prefecture, No. 31 . Okinawa Prefec-tural Board of Education, Naha. Google Scholar


Parker, J. D., Torchin, M. E., Hufbauer, R. A., Lemoine, N. P., Alba, C., Blumenthal, D. M., Bossdorf, O., Byers, J. E., Dunn, A. M., Heckman, R. W., Hejda, M., Jarošík, V., Kanarek, A. R., Martin, L. B., Perkins, S. E., Pyšek, P., Schierenbeck, K., Schlöder, C., Van Klinken, R., Vaughn, K. J., Williams, W., and Wolfe, L. M. 2013. Do invasive species perform better in their new ranges? Ecology 94: 985–994. Google Scholar


Pledger, S. and Efford, M. 1998. Correction of populations capture probability in capture-recapture studies of open populations. Biometrics 54: 888–898. Google Scholar


Punzo, F. 2001. The Mediterranean gecko, Hemidactylus turcicus: Life in an urban landscape. Florida Scientist 64: 56–66. Google Scholar


Radtkey, R. R., Donnellan, S. C., Fisher, R. N., Moritz, C., Hanley, K. A., and Case, T. J. 1995. When species collide: The origin and spread of an asexual species of gecko. Proceedings of the Royal Society B 259: 145–152. Google Scholar


Rödder, D. and Lötters, S. 2009. Niche shift versus niche conservatism? Climatic characteristics of the native and invasive ranges of the Mediterranean house gecko (Hemidactylus turcicus). Global Ecology and Biogeogrphy 18: 674–687. Google Scholar


Rödder, D., Solé, M., and Böhme, W. 2008. Predicting the potential distributions of two alien invasive house geckos (Gekkonidae: Hemidactylus frenatus, Hemidactylus mabouia). NorthWestern Journal of Zoology 4: 236–246. Google Scholar


Sakai, O. 2016. Size distribution suggests a seasonal effect on reproduction of Lepidodactylus lugubris on Okinawajima Island, Japan, the northernmost distributional area. Current Herpetology 35: 59–63. Google Scholar


Sakai, O. 2019. Behavioural tendencies associated with microhabitat use in a clonal gecko species living in the wild. Behavioral Ecology and Sociobiology 73: 64. Google Scholar


Sakai, A. K., Allendorf, F. W., Holt, J. S., Lodge, M., Molofsky, J., With, K. A., Cabin, R. J., Cohen, J. E., Norman, C., Mccauley, D. E., Neil, P. O., Parker, M., Thompson, J. N., and Weller, S. G. 2001. The population biology of invasive species. Annual Review of Ecology and Systematics 32: 305–332. Google Scholar


Schwarz, C. J. and Arnason, A. N. 2009. Jolly-Seber models in MARK. p. 1–52. In: E. Cooch and G. White (eds.), MARK: A gentle introduction. Available via Scholar


Shibata, Y., Kubota, M., and Ishimura, M. 1972. Mourning gecko (Lepidodactylus lugubris) from Okinawa and Yonaguni, Ryukyu Archipelago. Japanese Journal of Herpetology 5: 11–12. Google Scholar


Wessels, J. L., Carter, E. T., Hively, C. L., Hayter, L. E., and Fitzpatrick, B. M. 2018. Population viability of nonnative Mediterranean house geckos (Hemidactylus turcicus) at an urban site near the northern invasion front. Journal of Herpetology 52: 215–222. Google Scholar


White, G. C. and Burnham, K. P. 1999. Program mark: Survival estimation from populations of marked animals. Bird Study 46: S120–S139. Google Scholar


Yamashiro, S., Toda, M., and Ota, H. 2000. Clonal composition of the parthenogenetic gecko, Lepidodactylus lugubris, at the northernmost extremity of its range. Zoological Science 17: 1013–1020. Google Scholar
© 2019 by The Herpetological Society of Japan
Osamu Sakai "Population Density of a Clonal Gecko Species in Its Northernmost Range, the Ryukyus in Japan," Current Herpetology 38(2), 180-186, (31 August 2019).
Accepted: 4 July 2019; Published: 31 August 2019
Climate shift
invasive species
Lepidodactylus lugubris
population abundance
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