Abstract
The captive maintenance of healthy amphibian species requires an in depth knowledge of their dietary and environmental requirements. In New Zealand, only three of the four threatened native frog species within the genus Leiopelma are held in captivity. Each of these captive populations has suffered significant rates of disease and mortality, coupled with poor breeding success. To determine the suitability of current captive maintenance techniques used for Leiopelma, this thesis examined the differences between natural Leiopelma diets and environments and those provided to frogs in captivity.
Chapter 2 completes the most thorough dietary analysis of wild L. hochstetteri to date, identifying 23 different prey groups in 73 faecal pellets. Potential prey items were sampled using pitfall traps and this showed monthly variation that was significantly different to the composition of the diet. Different age classes were found to eat similar prey groups in different frequencies. The results of the faecal pellet study were used to formulate a captive diet for juvenile L. hochstetteri.
The diet analysis in Chapter 2 is followed by an investigation into the nutritional qualities of both invertebrates found in the natural diet of Leiopelmaand those fed to this genus in captivity (Chapter 3). Importantly, the diet of wild frogs was found to contain invertebrates which were rich in calcium and had positive calcium to phosphorus ratios. These attributes were lacking in all but one of the invertebrate species fed to captive frogs, meaning that current diets are likely to hinder bone growth and development and require amendment.
In order to inform dietary improvement, the efficacy of using the isopod Porcellio scaber to naturally increase calcium content in the diet of Leiopelma was assessed. This was made possible through a novel analysis of gut-retention time in L. archeyi, L. hochstetteri and L. pakeka. Calcium in P. scaber was found to be bioavailable to each Leiopelma species examined, with the highest calcium absorption occurring in L. archeyi and the lowest in L. pakeka. Porcellio scaber should thus be fed to all Leiopelma in captivity. Faecal analysis found that L. hochstetteri at Hamilton Zoo consume invertebrates which are self-introduced to their enclosures, indicating that their diet may be more nutritionally complete than previously assumed. Further recommendations on ways to improve the diets of captive Leiopelma are presented at the end of Chapter 3.
The designs of Leiopelma enclosures need to be assessed to ensure that they closely mimic the abiotic parameters of frogs’ natural habitats. Chapter 4 compared aspects of the microhabitats of wild Leioplema at Tapu, to those observed in Hamilton and Auckland Zoo enclosures. These included water and soil composition, annual changes in water and air temperature as well as relative humidity, and UV-B irradiance. The study also examined retreat site composition and age class associations within L. hochstetteri. Captive enclosures were shown to provide abiotic parameters close to those observed in natural Leiopelma habitat. Improvements that may further enhance the health and breeding success of captive Leiopelma are outlined.