Abstract
The rate of biodiversity loss is not slowing despite global commitments. Conservation translocations, the intentional movement and release of organisms to restore populations, are an emerging tool to help reduce species loss, but translocation success rates can be low. Recent reviews of and guidelines for conservation translocations emphasise the use of strategic approaches to improve translocation outcomes. Tuatara (Sphenodon punctatus) are endemic reptiles from New Zealand and the last surviving member of Rhynchocephalia. The Sphenodon genus was once widespread throughout New Zealand, but, following human arrival and the introduction of mammalian predators to the mainland, tuatara now naturally inhabit only 32 offshore islands. A long-term recovery goal is to re-establish populations of tuatara on the mainland and offshore islands. The aim of this thesis is to increase the likelihood that conservation translocations of tuatara will succeed. This was addressed through two approaches: 1) I compared the post-release performance and survival of captive-reared versus wild-caught juvenile tuatara, and 2) I applied correlative- and mechanistic-models to predict climatically suitable sites for tuatara.
Post-release performance has rarely been compared between captive-reared and wild-conspecific reptiles, and results have been mixed. In Chapters 2 and 3, I compared morphometric, ecophysiological and behavioural traits, resource selection and, ultimately, survival of juveniles in three groups (wild-caught from a warmer climate, captive-reared from a warmer climate and captive-reared from the local climate) released into Orokonui Ecosanctuary in southern New Zealand. For most metrics, including survival, post release performance of captive-reared and wild-caught juveniles were similar, and captive-reared groups sometimes differed between each other as much as between captive-reared and wild. These findings highlight the species-specific nature of translocation outcomes and the need for adaptive management in the field of reintroduction biology.
Populations might fail to establish following translocation, even when the most suitable founder animals are selected, unless they are released into suitable areas of habitat. A key aspect of planning is therefore the selection of suitable release sites that match the biotic and abiotic needs of the focal species under current and future climates. In Chapter 4, I used three widely applied correlative species distribution models to predict climatically suitable sites for future translocations. Despite discrepancies for future climates, the three correlative species distribution models projected an increase in area of climatically suitable habitat for tuatara. The thermal sensitivity of physiological rates is a key characteristic of organisms. In Chapter 5, I measured metabolic rate and rates of evaporative water loss in juvenile tuatara, over a range of temperatures. These metabolic and water loss data provide a firm basis for estimating the thermodynamic niche for tuatara. In Chapter 6, I use a biophysical model fitted with the physiological data to illustrate the use of a mechanistic model for free-roaming tuatara under current and future climates. This mechanistic model is the first for a free-roaming animal species in New Zealand and provides key information for tuatara conservation.
Taken together, my thesis makes an important contribution to the conservation science of tuatara and reptiles generally. The findings from this research are applicable to a wide range of species that are translocated for conservation benefit.