Hemidactylus frenatus has demonstrated a high propensity for competitive displacement of similar-sized and urban-adapted geckos. The ability of H. frenatus to replace locally native gecko species seems most pronounced in urban areas. H. frenatus is very well adapted to predation on concentrations of insects that gather along building walls near artificial lighting, seemingly more so than most endemic gecko species. H. frenatus also tends to be more aggressive and territorial, as well as, more tolerant of interspecific cohabitation and competition than endemic geckos. Such features allow it to successfully outcompete native species and exclude them from concentrated food sources. Studies have demonstrated aggressive, dominant behavior in H. frenatus over native geckos Nactus spp. on the Mascarene Islands and Lepidodactylus lugubris throughout Pacific islands. H. frenatus was frequently observed stalking, lunging towards and biting at other geckos. In some instances H. frenatus bit off their tails or ate them entirely. H. frenatus was also found to aggressively exclude endemic geckos from daytime refugia, making these native species more vulnerable to predation and adverse climatic conditions (Cole et al. 2005; Newberry & Jones, 2008). H. frenatus are also known to predate upon other small, usually juvenile lizards, such as Cryptoblepharus boutonii (Cole et al. 2005b).
There are many records of H. frenatus displacing or causing decline in native geckos throughout its introduced range ostensibly by competitive displacement. H. frenatus displaces endemic and 'Vulnerable (VU)' lesser night gecko (see Nactus coindemirensis in IUCN Red List of Threatened Species) and the endemic night gecko Nactus durrelli in the Mascarene Islands. It displaces both Nactus spp. from favored environments increasing their risk of predation and has proven to be a major cause in the decline of, the once thought extinct in the wild, N. coindemirensis (Cole et al, 2005; Jones & Cole, 2004). H. frenatus displaces Pacific island native Lepidodactylus lugubris in many locations and has demonstrated superior predation abilities. Experiments have demonstrated that H. frenatus consumes a disproportionately higher amount of insect prey than L. lugubris, thereby leaving it with less potential prey which decreases its body condition, fecundity, and ability to survive (Hanley et al 1995; Harvey et al 1998; Petren & Case, 1996). A similar predation study with Australian gecko Gehyra dubia also found H. frenatus to be a more formidable forager (Canyon & Hill, 1997). The displacement of Hemidactylus garnotii by H. frenatus throughout the Pacific basin has been attributed to behavioral interference from aggressive males. Furthermore, H. frenatus was also found to hybridize with H. garnotti in laboratory experiments (Dame & Petren, 2006).
Location Specific Impacts:
Competition: Hemidactylus frenatus competes with native geckos in Australia. It is said to have displaced natives Gehyra australis and Oedura rhombifer from the house gecko niche in some areas of northern Australia. O. rhombifer which was once abundant in Darwin, Queensland was reported completely absent in 2002 and is believed to have been displaced by H. frenatus (Couper etal,2007; Csurhes & Markula, 2009).
Disease transmission: Hemidactylus frenatus was found to host adult and nymphal forms of pentasome parasites Raillietiella frenatus and Waddycephalus sp. Infected specimens were collected from the Northern Territory and its surrounding islands but were not found in Northern Queensland. This is the first reported Australian occurence of R. frenatus which commonly occurs in H. frenatus in Southeast Asia and the Pacific (Barton, 2007).
The red gecko mite (Geckobia bataviensis) has also been found on H. frenatus in the Northern Territory and at Wynnum, south-east Queensland (Csurhes & Markula, 2009).
Christmas Island (Indian Ocean)
Competition: Although not evaluated, researchers believe Hemidactylus frenatus may adversely affect the endemic Christmas Island gecko (Lepidocatylus listeri) (Csurhes & Markula, 2009).
Competition: Hemidactylus frenatus competes with native geckos and other insectivores for insect prey species. Its abundance depletes insect prey for predators and can have significant impact on local ecology (Barquero & Hilje, 2005).
Competition: Hemidactylus frenatus competes with native geckos in Guam and has been implicated as a cause of their decline (Couper etal,2007).
Competition: Through the exploitation of food resources Hemidactylus frenatus has an indirect impact upon the endemic ornate day gecko (Phelsuma ornate) where the two species co-exist (Cole, 2005).v
Threat to endangered species: Hemidactylus frenatus displaces endemic and threatened lesser night gecko Nactus coindemirensis and the endemic night gecko Nactus durrelli in Mauritius and is thought to have contributed to the extinction of endemic night geckos in Reunion and Rodrigues. H. frenatus displaces Nactus spp. from favored environments increasing their risk of predation and has proven to be a major cause in the decline of, the once thought extinct in the wild, N. coindemirensis (Cole et al., 2005; Jones & Cole, 2004).
Competition: Hemidactylus frenatus is thought to be a potential threat to native gecko Christinus guentheri (Cogger etal,2005).
Reunion (La Réunion)
Threat to endangered species: Hemidactylus frenatus displaces endemic and threatened lesser night gecko Nactus coindemirensis and the endemic night gecko Nactus durrelli in Mauritius and is thought to have contributed to the extinction of endemic night geckos in Reunion and Rodrigues. H. frenatus displaces both Nactus sp. from favored environments increasing their risk of predation and has proven to be a major cause in the decline of, the once thought extinct in the wild, N. coindemirensis (Cole et al., 2005; Jones & Cole, 2004). Through the exploitation of food resources H. frenatus has an indirect impact upon the endemic ornate day gecko (Phelsuma ornate) where the two species co-exist in Mauritius and may have a similar impact upon endangered Phelsuma populations in Reunion (Cole, 2005).
Reduction in native biodiversity: Hemidactylus frenatus is known to predate on invertebrates (Ashmole and Ashmole, 2000 in Varnham, 2006).
Hawaii (United States (USA))
Competition: Hemidactylus frenatus is believed to cause a decline of Polynesian-introduced gecko Lepidodactylus lugubris in Hawaii. Specific declines were found to occur around artificial lighting which both species use to attract prey at night. The larger H. frenatus appears to outcompete L. lugubris for prey species. Researchers also found that L. lugubris tended to avoid proximity to H. frenatus and have lower fecundity in its presence. Finally, H. frenatus is known to prey on L. lugubris juveniles (Brown etal,2002).
Similar competitive exclusion in urban and suburban environments has occurred between H. dactylus two other Polynesian-introduced geckos (Hemidactylus garnotii) and (Gehyra mutilata) (Case & Bolger, 1991).