Presence of Asian House Gecko Hemidactylus frenatus across an urban gradient in Brisbane: influence of habitat and potential for impact on native gecko species Author Newbery, Brock, Jones, Darryl Published 2007 Book Title Pest or Guest: The Zoology of Overabundance Copyright Statement © 2007 Royal Zoological Society of NSW. The attached file is reproduced here in accordance with the copyright policy of the publisher. Please refer to the book link for access to the definitive, published version. Downloaded from http://hdl.handle.net/10072/18554 Link to published version http://www.rzsnsw.org.au/ Griffith Research Online https://research-repository.griffith.edu.au Presence of Asian House Gecko Hemidactylus frenatus across an urban gradient in Brisbane: influence of habitat and potential for impact on native gecko species Brock Newbery1 and Darryl N. Jones1,2 1Suburban Wildlife Research Group, Australian School of Environmental Studies, Griffith University, Nathan, Qld. 4111, Australia. 2Corresponding author: Darryl Jones, [email protected] The Asian House Gecko Hemidactylus frenatus is an internationally significant invasive reptile which T has spread rapidly though the Pacific and elsewhere and has been implicated in the decline and extinction of a number of native gecko species. Although present in Darwin for some time, the C species has only recently become widespread in the Brisbane region. We investigated the density A and distribution of this and two native house-dwelling geckos in urban, suburban and bushland R environments within Brisbane. The spatially clumped insect resources associated with external light T sources were effectively utilised by both urban and suburban populations of Asian House Geckos, S suggesting likely competitive interactions between the species on structures where the species co-existed. At this time, there is no evidence of the introduced species living away from buildings B in the Brisbane region. A Key words: Asian House Gecko, invasive species, urban ecology Introduction displacement of other human-associated geckos (Greer 1989, Case et al. 1994, Petren and Case 1996, Brown Native to Asia and the Indo-pacific, the Asian House et al. 2002, Cole et al. 2005). Perhaps the most studied Gecko Hemidactylus frenatus is rapidly becoming a interaction is that which occurs between the Asian House cosmopolitan species (Worthington-Wilmer et al. 2003, Gecko and the Mourning Gecko Lepidodactylus lugubris Vences et al. 2004) with a distribution closely associated on islands throughout the Pacific (Case et al. 1994). with human habitation (Greer 1989). In the last 60 years Many forms of competition have been experimentally it has successfully colonised island habitats throughout demonstrated to exist between these species. Behavioural the Pacific region and the Americas, where it has been dominance is evidenced by the exclusion of the Mourning implicated in the decline and extinction of numerous Gecko from concentrated food resources found around other gecko species (Case et al. 1994, Hanley et al. 1998, electric lights. This dominance is not displayed as overt Brown et al. 2002, Worthington-Wilmer et al. 2003, Cole interspecific aggression, but rather, by an avoidance et al. 2005). response resulting in the Mourning Gecko occupying less The Asian House Gecko is highly synanthropic, regularly favourable foraging positions (Petren et al. 1993). The colonising human settlements and foraging on insects reduced resource acquisition in the Mourning Gecko attracted to external lights. It is thought that the species’ translates into a reduction in body condition, fecundity global distribution has increased since about the 1950s and survivorship (Case et al. 1994, Petren and Case 1996). due to increases in international shipping and cargo Significantly, in the absence of Asian House Geckos, movement (Greer 1989). Microscopic setae on the Mourning Geckos on some Pacific islands were eight sub-digital lamellae increase the climbing ability of the times more abundant on buildings than on neighbouring species (Russell 2002, Pianka and Sweet 2005), allowing islands where the two species were present together (Case it to move and forage freely on the large, structurally et al. 1994). simple, vertical and inverted surfaces (such as walls and In Australia, Asian House Geckos were first recorded in windows) often illuminated by external light sources. This 1845 at the now abandoned settlement of Port Essington superior clinging ability also affords the species access to in the Northern Territory (Greer 2004). Thereafter the high crevice spaces for egg deposition and refuge from species apparently went unrecorded until the 1960s predators. These characteristics increase its potential to when a population was discovered in suburban Darwin pass undetected in transit on shipping containers and (Swanson 1990). The first record in Brisbane was made cargo. Furthermore, the female’s capacity for functional in 1983, when customs and quarantine staff observed sperm retention facilitates successful establishment upon an apparently breeding population around the Brisbane introduction to an new location due to a reduced necessity wharves (Covacevich 2001). After an initial period of for mate acquisition (Murphy-Walker and Haley 1996). patchy distribution limited to suburbs adjacent to the During the Asian House Geckos numerous colonisation Brisbane Port, the species expanded dramatically during events, it has shown a propensity for competitive the 1990s and is now the most frequently observed house- Pp 59 - 65 in Pest or Guest: the zoology of overabundance, edited by Daniel Lunney, Peggy Eby, Pat Hutchings and Shelley Burgin. 2007. Royal Zoological Society of New South Wales, Mosman, NSW, Australia. Newbery and Jones dwelling gecko in Brisbane (Newbery et al. 2005). It is also sites (most represented by an individual single-storey widely distributed through coastal regions of Queensland dwelling) were selected from these four habitat types. (Wilson and Swan 2003). Due to a limited number of bushland areas containing Studies of the invasive nature of the Asian House Gecko structures similar in size to a residential dwelling, only and potential competitive impacts on native geckos in three bushlands were surveyed. Australia have only recently been undertaken. Keim Sites were located in the following locations or Brisbane (2002) compared the responses of Asian House Gecko suburbs: Urban (Logan Central, Auchenflower, Spring populations to habitat edges on suburban and bushland Hill, Newstead); Suburban (Carole Park, Wynnum, sites in Brisbane and Darwin (Darwin’s Asian House Tarragindi, Easton’s Hills); Rural (Carbrook, Waterford Gecko population being at least 20 years older than West, Pallara, Closeburn); and bushland (Brisbane Forest Brisbane’s). Although it is often suggested that Asian Park, Karawatha, Daisy Hill). House Geckos are confined to anthropogenic habitats, Sites were visited during the warmer months of January- in Darwin Keim (2002) found ‘significant densities’ of April; geckos remained active throughout this period Asian House Geckos up to 150 m into bushland. In in Brisbane. The number of all house-dwelling geckos contrast, Brisbane’s Asian House Geckos tended to be at found at each site was determined using auditory and lower numbers on houses approaching suburban bushland visual sampling techniques. The external surfaces of reserves and to be absent within bushland itself. During each structure (walls, eves, verandas, foundations etc, her Brisbane surveys, Keim (2002) also recorded the but excluding under-houses where applicable) were Asian House Gecko, Dubious Dtella Gehyra dubia and systematically searched for evidence of geckos using a Robust Velvet Gecko Oedura robusta present together on suburban sites when in close proximity to bushland. hand-held torch and small binoculars (Case et al. 1994, Keim 2002, Newbery et al. 2005). Each site was surveyed Information on the density and distributions of Australian for an average of 15 minutes starting no earlier than 6.30 populations of the Asian House Gecko remains pm and finishing no later than 9.00 pm. Surveys were fragmentary. A preliminary investigation in Brisbane not conducted on nights with rain or when the ambient (Newbery et al. 2005) showed that significantly greater temperature was below 20°C. numbers were present on residential dwellings within the highly urbanised inner city suburbs compared to houses Species identification was confirmed by observation of in the less structurally dense outer suburbs. Keim (2002) phenotypic characteristics of each species. For the Asian suggested that the densities of Brisbane’s population may House Geckos (Figure 1), confirmation was based on be restricted due a comparatively cooler climate than the presence of transverse blunt tail tubercles (Wilson Darwin and / or due to the negative effects of interactions and Swan 2003) and detection of one of the three with native arboreal geckos. characteristic vocalisations of the species (Greer 1989), the most common and easily identifiable being the ‘chuck, The invasive nature of the Asian House Gecko in human chuck, chuck’ call. As the Dubious Dtella (Figure 2) bears habitats throughout the warmer regions of the world is some resemblance to the Asian House Gecko in size and now well recognised (Greer 1989, Meshaka et al. 1994, colouring (B. Newbery, pers. obs.), visual confirmation Petren and Case 1996, Hanley et al. 1998, Vences et al. was based on the lack of the blunt