The impact of invasive species on reptile communities

A completed 3 year PhD study by Nik Cole

a gecko
© Mammal Research Unit
Male Phelsuma ornata, Round Island.
Photo by Nik Cole

My research interests are in the field of invasive biology, in particular the impact of introduced predators and competitors on native and endemic reptile communities. The devastating effect of invasive species on global biodiversity is currently of enormous scientific and public concern. In recent times, most recorded extinctions have occurred on oceanic islands, mainly as a result of introduced predatory mammals. The role of introduced competitors, however, is poorly understood.

From 2002-2005, I investigated the impact of the competitive house gecko, Hemidactylus frenatus, which had been implicated in the decline of the endemic day gecko, Phelsuma ornata, and localised extinctions of endemic night geckos, Nactus spp., in Mauritius, Indian Ocean. During my research I compared patterns of niche utilisation and interaction between these species to determine the competitive mechanisms potentially responsible for present gecko abundances and distributions throughout the Mauritian islands.

I found that in synergy with habitat destruction, exploitative competition for food resources has been a likely determinant in the decline of P. ornata. The impact of this competitive interaction on P. ornata was two-fold: (i) increased intraspecific aggression through environment- and H. frenatus-related food limitation, and (ii) enhanced parasite-mediated apparent competition in the presence of H. frenatus.

Past competitive interactions between the Nactus species and H. frenatus were most likely along the space and, for some, food niche axes. In experimental enclosures, the Nactus species had no effect upon one another, but were excluded from refugia through aggressive and predatory interactions with H. frenatus. The increased risk to shared enemies would likely have caused Nactus extinction from islands invaded by H. frenatus.

Substrates with crumbly surfaces were shown to exclude H. frenatus from habitats utilised by Nactus species on the basis of toe morphology, and have enabled a newly discovered Nactus population to survive in the presence of H. frenatus. These findings, in conjunction with the competitive role of H. frenatus have important implications for the conservation of Mauritian gecko populations.

This research was conducted in association with the Mauritian Wildlife Foundation, supported by the Natural Environment Research Council and part funded by the Zoological Society of Wales and the Amphibian Reptile & Insect Association.

Part of this research has been published:

Cole, N.C., Jones, C.G. & Harris, S. (2005) The need for enemy-free space: the impact of an invasive gecko on island endemics. Biological Conservation 125: 467-474.
doi: 10.1016/j.biocon.2005.04.017

Leinwand, I., Kilpatrick, A.M., Cole, N., Jones, C.G., & Daszak, P. (2005) Drivers of coccidial prevalence in endemic and introduced lizards of Mauritius. Journal of Parasitology 91: 1103-1108.

Cole, N.C. (2004) A novel technique for capturing arboreal geckos. Herpetological Review 35: 358-359.

Contact details

Dr Nik Cole
Mammal Research Unit
School of Biological Sciences
University of Bristol
Woodland Road
Bristol BS8 1UG, U.K.

Telephone: 0117 9287593
Email: Dr Nik Cole