Understanding range expansion of Asian house geckos (Hemidactylus frenatus) in natural environments

Barnett, Louise Katherine (2017) Understanding range expansion of Asian house geckos (Hemidactylus frenatus) in natural environments. PhD thesis, James Cook University.

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Over the past 50 years accidental introductions of invasive species have accelerated due to globalisation and increased transit efficiency. Once established, invasive species may affect biodiversity through predation, competition or hybridisation with native taxa, or through the introduction of novel parasites. The impacts of invasive species are mediated by their distribution within the introduced range, and it is important to understand the processes controlling range expansion of invasive species. Human-associated invasive species are often overlooked as potential threats to native species in natural environments, due to their perceived restriction to anthropogenic habitats. It is, nonetheless, likely that some of these species will eventually spread into natural habitats due to their broad global distributions, propensity to establish large populations in urban areas and the ever-expanding reach of human infrastructure. Human-associated species also present ideal systems to assess the factors driving range expansion across abrupt ecological boundaries because of the stark differences between urban areas and surrounding natural environments, and because urban areas often provide multiple semi-independent invasion fronts to compare within the same geographic region.

This thesis investigates the factors that facilitate range expansion of a human-associated invasive species, the Asian house gecko, Hemidactylus frenatus, into natural habitats in the Townsville region of northern Australia. It outlines how demographic factors, environmental factors, morphological divergence and parasitism affect range expansion, touches on the potential impacts of H. frenatus in these environments and establishes an effective method for H. frenatus detection.

Chapter 2 investigates whether there are established populations of H. frenatus in natural environments, and assesses whether environmental or demographic factors affect expansion into natural habitats. This was achieved by surveying ten transects in the Townsville region of north Queensland every month for a year. Each transect was made up of five sites positioned every 500 m from the urban edge up to 2 km into surrounding woodland. This work revealed that the most important factors facilitating expansion into woodland environments are propagule pressure (i.e., relative abundance of H. frenatus at the urban edge) and the number of years since H. frenatus established in the urban area. Environmental factors, such as coarse habitat structure and size of the urban area did not affect range expansion.

Chapter 3 examines whether morphological divergence occurs during expansion of H. frenatus into natural environments across multiple semi-independent invasion fronts. Hemidactylus frenatus were collected from paired urban and woodland sites for assessment of body and toe morphology. Results indicate that H. frenatus have morphologically diverged in natural environments, but the direction of some trait shifts differed between the three semi-independent invasion fronts studied.

Chapter 4 investigates the potential impact of parasites during range expansion of H. frenatus into natural environments, as well as the potential for parasite transmission between H. frenatus and co-occurring native geckos. There was no evidence for transmission of native or invasive Geckobia mites between H. frenatus and native geckos; however, in this system H. frenatus can host native Australian pentastomes of the Waddycephalus genus. The relatively high density of H. frenatus in natural habitats makes parasite spillback of Waddycephalus to native host species a concern.

Having demonstrated that H. frenatus can establish large populations in natural environments, it is important to understand the most effective technique for early detection of this species. Chapter 5 uses data collected over multiple site visits to investigate which abiotic factors affect individual-level detection probability of H. frenatus. Binomial mixture models are used to assess the optimal conditions for detecting H. frenatus in natural environments and to compare the efficiency of listening and visual surveys. I found that multiple site visits are necessary for detection of this species. However, detection probability can be maximised by choosing to survey in appropriate conditions, and through pairing five-minute listening surveys and 15-minute visual searches.

This thesis assesses a number of factors known to affect range expansion of invasive species and investigates their importance in relation to the establishment of Asian house geckos in natural environments. It highlights the complex nature of range expansion across abrupt habitat boundaries and demonstrates that human-associated species can provide ideal systems to investigate range expansion and rapid adaptive responses.

Item ID: 51755
Item Type: Thesis (PhD)
Keywords: detection, Geckobia, Hemidactylus frenatus, house geckos, invasive species, invasive, lag period, parasites, range expansion, seasonal, survey effort, Townsville region, urbanization, Waddycephalus, woodlands
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Additional Information:

Chapter 2 (publication) is not available through this repository.

Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Barnett, Louise K., Phillips, Ben L., and Hoskin, Conrad J. (2017) Going feral: time and propagule pressure determine range expansion of Asian house geckos into natural environments. Austral Ecology, 42 (2). pp. 165-175.

Date Deposited: 13 Dec 2017 02:05
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060208 Terrestrial Ecology @ 25%
05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050103 Invasive Species Ecology @ 50%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050202 Conservation and Biodiversity @ 25%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960806 Forest and Woodlands Flora, Fauna and Biodiversity @ 50%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 50%
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