School of Botany - Theses
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ItemEvaluating scientific approaches to the conservation of threatened trees : the monkey puzzle tree in South America(University of Melbourne, 2002)As the loss and fragmentation of habitat suitable for many species continues, understanding the processes that threaten small or fragmented populations and improving methods to conserve them IS becoming increasingly important. This thesis investigated two key scientific approaches currently used in the conservation of threatened trees: conservation genetics and population viability analysis. The benefits and drawbacks of these approaches to conserving threatened species were evaluated using a case study of the monkey puzzle tree (Araucaria araucana), a vulnerable South American species of exceptional ecological, economic and cultural importance. Two techniques were used to characterise genetic heterogeneity within and among populations of monkey puzzle: neutral DNA markers (RAPDs) and quantitative traits (carbon isotope discrimination and root mass ratio). Both the level and pattern of genetic variation estimated using the different techniques were essentially uncorrelated. Neutral markers failed to detect an important quantitative genetic divergence across the Andean Range relating to drought tolerance. The potential problems associated with making recommendations for conserving the genetic resource of threatened species based solely on neutral marker studies were discussed. Fragmented populations of monkey puzzle were investigated for the negative effects of genetic erosion and associated deleterious demographic consequences. This was achieved through a glasshouse experiment and further RAPD analysis. A trend was detected that indicated reduced survivorship of seedlings from small populations of monkey puzzle, although no trend was detected for neutral marker diversity. Two advances in the statistical analysis of genetic data were employed to determine these trends: bootstrapping to adjust for sample size bias and power analysis. It was demonstrated that failure to analyse genetic data correctly has reduced the ability of previous studies to determine the real genetic consequences of habitat fragmentation. A stage-based population model was constructed to examine the likelihood that populations of monkey puzzle will persist and recover given the present level of seed harvesting and other human impacts, in the presence of catastrophic events such as volcanic activity and fire. The model indicated that the probability of a 10% increase over the next ICQ years is very low given the current seed harvesting and burning regime. It was demonstrated that the risk of fire and volcanic activity and their potential effect on population trends should be considered in the conservation management of monkey puzzle, particularly in reserve design. A population model can potentially be of great value in the case of a long-lived, slow-growing species such as the monkey puzzle tree, as It is otherwise difficult to foresee the long-term consequences of current management practices. Finally, environmental, demographic and genetic information were combined in a population model to determine the relative importance of these factors and their interactions for the persistence of monkey puzzle. An empirical approach was used to incorporate genetic effects in the model, rather than a standard mechanistic genetic model, because the mechanisms of genetic erosion in wild populations of plants are poorly understood and the subsequent effect on population fitness is otherwise complex and difficult to quantify. Recommendations were made regarding future attempts to synthesise genetic and demographic influences on fragmented populations to inform conservation management.