A comparison of site occupancy and morphology between Litoria raniformis in Central Otago, New Zealand and Victoria, Australia
Many amphibian species across the globe are at high risk of extinction. Alien species, overexploitation, land-use change, climate change, chemicals, and infectious diseases are all having devastating effects on amphibians. Land-use changes, in particular, are responsible for the declines of many frog species in Australia. However, the Australian frog Litoria raniformis was introduced to New Zealand over 150 years ago and has subsequently colonised the country. This success in a foreign country contrasts the Endangered status of L. raniformis in Australia, but it presents unique opportunities for research and management in New Zealand, which can aid in the conservation of the species in Australia. The overarching goal of this research was to investigate whether L. raniformis in Central Otago, New Zealand have experienced any changes in habitat occupancy or morphology since their move from Australia. I used two groups of L. raniformis in this comparison including populations in Victoria, Australia and populations in Central Otago, New Zealand. The first aim of this research was to investigate which habitat features determine occupancy of L. raniformis and how habitat differs in Central Otago compared to Victoria. Answering this question required examining occupancy patterns of L. raniformis, and the availability of habitat features. This aim was achieved by conducting habitat assessments on sites in Central Otago and comparing them to habitat assessments already done in Victoria using the same methods. New Zealand and Australia are very different countries regarding both biotic and abiotic features, thus we would expect to see differences in the indigenous and introduced range of L. raniformis. However, amphibians are particularly susceptible to habitat alterations and the presence of habitat features similar to those in the native range has been found to support introduced species. Although, some species have been found to thrive when introduced to sites containing novel habitat features. Therefore, I predicted that similar habitat features across Central Otago and Victoria would predict occupancy of sites; but I also predicted that some difference in sites might be contributing to the abundant population of L. raniformis in New Zealand. There was a trend that L. raniformis preferentially occupied sites that had a higher percentage cover of submerged vegetation over those with low to no cover, in both Central Otago and Victoria. Additionally, Central Otago had significantly more submerged vegetation than Victoria. This finding may contribute to the relative success of L. raniformis in New Zealand compared to Australia. Submerged vegetation is an important habitat feature for L. raniformis reproduction; a higher percentage of submerged vegetation in ponds may enhance breeding success. The second aim of this study was to investigate whether any shifts in body size had occurred in Central Otago L. raniformis compared to those in Victoria. Answering this question required populations of Central Otago L. raniformis to be weighed and measured, and then compared to the same data already collected in Australia. Litoria raniformis has been in New Zealand for over 150 years and may have experienced changes in morphology in order to adapt to New Zealand’s conditions. Furthermore, Central Otago reaches lower minimum temperatures than Victoria and is on average cooler. According to Bergmann’s Rule, this would suggest that L. raniformis may be larger in Central Otago than in Victoria as a larger body size is more efficient at maintaining heat due to the increased body size: surface ratio. Moreover, insular shifts are known to affect morphology through changes in biotic interactions, of which there would be many in the move from Australia to New Zealand. Therefore, I predicted that L. raniformis in Central Otago would be on average larger than conspecifics in Victoria. This prediction was incorrect as female L. raniformis in New Zealand were smaller, while males were very similarly sized. Competition, food availability, predation, or differing growth periods may have contributed to this effect. However, this requires further research. The present study demonstrated that L. raniformis in New Zealand exhibit slight differences in site occupancy and morphology. This study has also provided a start to utilising the populations of L. raniformis in New Zealand for research and management techniques that can be applied in Australia.
Advisor: Bishop, Phil; Tingley, Reid
Degree Name: Master of Science
Degree Discipline: Zoology
Publisher: University of Otago
Keywords: New Zealand; southern bell frog; ranoidea raniformis; Australia; ecology; biology; morphology; habitat occupancy; litoria raniformis; growling grass frog
Research Type: Thesis