The conservation biology of Pittosporum obcordatum: conservation genetics and habitat specificity
Thesis DisciplinePlant Biology
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Pittosporum obcordatum (Pittosporaceae) is a threatened lowland shrub, primarily found in alluvial sites with widely separated populations throughout the North and South Islands of New Zealand. Threats to P. obcordatum include small population size, habitat loss, competition with exotic plants and grazing from introduced mammals. The primary goal of this thesis was to was to better understand genetic and ecological factors that could assist with the conservation of P. obcordatum. I used Inter\Simple Sequence Repeat (ISSR) markers to study the genetic diversity of 128 individuals from 10 populations of P. obcordatum from Kaitaia to Fiordland. Populations of P. obcordatum had low to moderate genetic diversity, and smaller populations contained less genetic diversity than larger populations. A high degree of geographic genetic structure was found, suggesting little or no recent gene flow between populations. Small population sizes and geographic isolation of the populations likely have an effect on this. Based on this data, recommendations are made for site\specific restoration planting designed to maximise population size and genetic diversity, accompanied by conservation strategies targeting threats from land use. Further, a newly discovered population of P. obcordatum on Banks Peninsula has been found growing on a hillside, and this thesis investigated why the species was growing in an unexpected habitat. When pot\grown seedlings from Banks Peninsula and a Fiordland alluvial flat population were subjected to drought, mortality was lower for Banks Peninsula seedlings than for Fiordland but not significantly so. When radishes (Raphanus sativus) were used as a phytometer, Banks Peninsula soil produced significantly less biomass than soil from three alluvial flats. Taken together, these findings indicate that slope and soil fertility have less of an impact on the success of P. obdorcatum than would previously have been assumed based on its alluvial sites, indicating that further populations may yet be found on other hillsides or in less fertile areas. Search and further genetic study of such populations are therefore recommended in order to elaborate on the habitat and genetic profile advanced by this research, allowing for a well\ rounded approach to conservation planning.