Amphibians are suffering extinctions and range contractions globally. This is caused by numerous factors and most of them are related to human activities. The overall aim of this thesis was to make a significant contribution to the conservation of the endemic amphibian Leiopelma hochstetteri through research. This was achieved by focusing in two of the main conservation issues for this species, the need for standardised and robust monitoring techniques to detect trends and changes in populations, and the determination of the prevalence of chytridiomycosis, caused by the amphibian chytrid fungus (Batrachochytrium dendrobatidis). Two populations of the Auckland Region were selected for this study, one on the mainland (Waitakere Ranges) and the only known offshore island population of this species (Great Barrier Island). For both study sites different monitoring methods were used to obtain some population parameters. Site occupancy models of MacKenzie et al. (2002) gave reliable site-specific estimations of occupancy and detection probability using covariate information and presence-absence data collected from 50 sites in the Waitakere Ranges and four repeated visits during 2008. Elevation and distance searched were found to have an important effect on occupancy levels, while time taken to search the site was important variable determining detection probabilities. Also, parameters were estimated for three age classes separately. Statistical models were used to infer abundance from occupancy analysis, and results were compared with the distribution of relative abundances obtained from repeated transect counts and an established sight/re-sight criterion. In addition, the use of surrogate measures for relative abundance was explored. Detection probability and the distance to first frog found were found to have a significant correlation with relative abundance. These measures can be used to infer relative abundance in future site occupancy surveys. Two surveys and a pilot site occupancy survey were conducted on Great Barrier Island, and presence of frogs was confirmed atthe northern block, and in a small seepage in the central block. No new locations were found. Waitakere Ranges and Great Barrier Is. populations were tested for the presence of chytridiomycosis, and all frogs sampled tested negative (n = 124) which means that if present chytridiomycosis prevalence is lower than 5% with a 95% confidence interval. This and previous evidence suggests that L. hochstetteri may be resistant or immune to the disease. However, to confirm this additional studies are needed.
| Identifer | oai:union.ndltd.org:ADTP/269449 |
| Date | January 2009 |
| Creators | Puig, Virginia Moreno |
| Publisher | Massey University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
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