School of BioSciences - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemOptimal management of metapopulations across space and time( 2016)Many threatened and invasive species occupy collections of spatially separated populations subject to local extinction and colonisation, known as metapopulations. Although they occur naturally, metapopulations are becoming increasingly prevalent throughout the world due to habitat loss and fragmentation. To increase the persistence of threatened metapopulations, or decrease the persistence of invasive ones, managers must decide how, where and when to spend limited resources across space and time. In this thesis, I integrate quantitative models with decision theory to predict the persistence of metapopulations in response to management alternatives. This thesis is divided into six chapters. The first chapter provides a general introduction to metapopulations and decision theory. The second chapter explores when, where and how to manage threatened metapopulations when the dynamics of these networks are poorly understood. Adaptive management has been applied to ecological problems containing considerable uncertainty, but is yet to guide the restoration of metapopulations. I develop a framework to optimally manage metapopulations using adaptive management when there is uncertainty in the rate of colonisation between patches. I develop a case study for the threatened bay checkerspot butterfly (Euphydryas editha bayensis) and demonstrate how best to manage the population while learning about its dynamics over time. The third chapter examines when to add a patch to a threatened metapopulation to compensate for destruction of another due to urbanisation or agricultural development. I develop spatially explicit metapopulation models for two threatened Australian species – the growling grass frog (Litoria raniformis) and the southern emu-wren (Spititurus malachurus intermedius) – and determine when it is optimal to add a patch to each metapopulation if the budget available to managers accrues interest over time. I find that there are many occupancy states of each metapopulation where it is optimal to delay habitat creation until well-after habitat destruction has occurred. The second half of this thesis focuses on invasive metapopulations. Chapter 4 develops a rule for determining when to increase the colonisation rate of metapopulations susceptible to three types of threat – an abiotic threat (i.e. fire, flood or drought), a generalist threat, and a specialist threat (i.e. predators, pathogens or disease). When considering habitat corridors as a management strategy, I show that managers must consider not only the type of threat acting on a metapopulation, but also how a threat might also respond to increased colonisation of a focal species. In some instances, increasing the colonisation rate can be detrimental to metapopulation persistence because of increased exposure to threats occupying the same habitat. The fifth chapter examines which patches of suitable habitat should be managed to contain the spread of one of the worst invasive species in Australia, the cane toad (Rhinella marina). A previously published model predicts the spread of toads can be contained by managing as few as 100 artificial water bodies (such as dams) in north-west Australia. I revise this model to address concerns raised by potential end-users, and find the most cost-effective location for a barrier to contain toad spread. In all of the scenarios tested cane toads could be contained from moving west from Northern Australia, at a cost of approximately $4.5 million over the next 50 years. Finally, Chapter 6 summarises the main findings of this thesis and discusses important areas of future research.