Abstract
Habitat modification is one of the largest threats to amphibians worldwide, yet research investigating habitat modification impacts and management responses is often limited. Consequently, there is a necessity to address such issues, particularly for rare Hochstetter’s frog (Leiopelma hochstetteri) populations that inhabit mature pine plantations in New Zealand. Fortunately, small populations at Torere Forest (Bay of Plenty, North Island) have received conservation attention following concerns over future pine harvesting. Possible management options are still in their infancy, but it is likely that a mitigation translocation via assisted colonisation will be required, even though a large-scale translocation for Hochstetter’s frogs has not occurred before. Orokonui Ecosanctuary (Dunedin, South Island) was selected as a potential translocation site primarily because future global warming scenarios suggest that southern regions may become more favourable for Hochstetter’s frogs than in their northern current distribution. However, the current cool climate at Orokonui Ecosanctuary is a concern as studies have concluded that Hochstetter’s frog populations are strongly associated with warm climates that frequently reach 20˚C or more. Therefore, the aims of this thesis were to investigate how Hochstetter’s frog populations and individuals are influenced by a modified environment and to assess whether a translocation to Orokonui Ecosanctuary is indeed feasible regarding identifying suitable areas of habitat and the effect of a cool climate on frogs.
In order to address these aims, this study examined population parameters and individual fitness, and the resource selection of Hochstetter’s frogs between mature pine plantations and native forests, followed by identifying suitable areas of habitat in Orokonui Ecosanctuary. The quality of the thermal environment at Torere Forest and Orokonui Ecosanctuary was also measured, along with the thermal preference and physiology of captive frogs exposed to cool temperatures. Overall, there were no differences in population parameters and individual body condition between the habitats, which suggested that mature pine plantations may not negatively affect populations and might even provide essential habitat. As for resource selection, the most important resources used by Hochstetter’s frogs were cobble habitat and logs, particularly in pine plantations. These resources were available in Orokonui Ecosanctuary, thus suitable areas of habitat were predicted to be present. However, results from the lab suggested that the thermal environment at Orokonui Ecosanctuary may be thermally challenging for Hochstetter’s frogs, particularly considering captive frogs mainly preferred temperatures between 15.3 - 20.9 ˚C (central 50%) and were unable to digest slaters in cool conditions. Digestion of crickets and locusts did occur however, whilst temperatures were reduced during the acclimation period. Furthermore, gut retention times and weights increased in cool conditions, which highlighted that temperature largely influences these physiological responses. Nevertheless, studies have shown that Hochstetter’s frogs may exhibit thermoregulatory behaviour to optimise the thermal environment. Such behavioural responses are useful as Hochstetter’s frogs often inhabit shallow substrata where thermal conditions are possibly near or at equilibrium with cold temperatures during winter. Moreover, given their generalist diet and often low proportions of slaters ingested, results from this study suggest that energy uptake may occur during winter and that digestion of major dietary components might not be largely affected by cold temperatures.
A translocation to Orokonui Ecosanctuary therefore seems feasible, but further investigations are necessary. Further, management tools such as long-term monitoring, trial transfers, and continued stakeholder support are essential for conserving the Hochstetter’s frog populations in Torere Forest. In doing so, the management of these populations will provide a foundation for the future conservation of this threatened species, especially regarding translocations that are yet to occur.