Research Priorities

• Polymer systems - can we model degradation and thermal fragmentation kinetics?
• Control of population networks - how should we optimally trade off returns from protection versus creation of habitat?

Researchers

• Chief Investigator: Phil Pollett
• Research Fellow: Ross McVinish
• PhD student : Fionnuala Buckley
• PhD student : Thomas Taimre
• 2008-2009 Vacation Scholar: Chung Kai Chan

Collaborating Researchers

• Dr Mark Flegg, Queensland University of Technology
• Dr Dmitri Gramotnev, Queensland University of Technology
• Prof Hugh Possingham, University of Queensland
• Dr Joshua Ross, University of Cambridge
• Dr David Sirl, University of Nottingham

Research Projects Completed

• Modelling degradation and thermal fragmentation kinetics in polymer-like systems

  Project leader: Phil Pollett
  Researchers: Mark Flegg (Queensland University of Technology), Dmitri Gramotnev (Queensland University of Technology)

  We have developed an explicit theory of degradation and thermal fragmentation kinetics for polymer-like systems and aggregates with multiple bonds in the presence of evaporation and condensation (restoration) of bonds. The analysis was conducted on the basis of the determining an explicit expression for the distribution of first passage time to state zero (fragmented state) in the Ehrenfest diffusion model in continuous time. We assumed that multiple bonds in any link between primary elements in the aggregate do not interact and that the coagulation rate after thermal fragmentation of the aggregates was negligible. We demonstrated that even small condensation rates (of order 10 times smaller than the rates of bond evaporation) may have a significant effect on typical evolution times for the degrading aggregates and can result in a strong accumulation of nanoaggregates in the intermediate fragmentation modes. The simple asymptotic (predominantly exponential) behaviour of the obtained solution at large evolution times was analyzed. It is expected that our results will proved to be important for the investigation of degradation kinetics in a variety of polymer-like systems with multiple bonds, including self-arranged structures, polymer networks, different types of nanoclusters and their thermal fragmentation, et cetera.

  Research outputs

  Flegg, M.B., Pollett, P.K. and D.K. Gramotnev (2008) Ehrenfest model for the condensation and evaporation processes in degrading aggregates with multiple bonds. Physical Review E 78, 031117. [Also appeared in Volume 18, Issue 12 of the Virtual Journal of Nanoscale Science & Technology.]

• Optimal control in population networks

  Project leader: Phil Pollett
  Researchers: Hugh Possingham (UQ), Joshua Ross (University of Cambridge), David Sirl (University of Nottingham)

  Habitat loss and fragmentation has created population networks (metapopulations) where there were once continuous populations. Ecologists and conservation biologists have become interested in the optimal way to manage and conserve these populations. Several researchers have considered the effect of patch disturbance and recovery on metapopulation persistence, but almost all such studies assume that every patch is equally susceptible to disturbance. We investigated the influence of protecting patches from disturbance on population persistence, and used a stochastic metapopulation model to explain how to optimally trade off returns from protection of patches versus creation of new patches. We considered the problem of finding, under budgetary constraints, the optimal combination of increasing the number of patches versus increasing the number of protected patches. We discovered that the optimal trade-off depends on all properties of the system: species dynamics, dynamics of the landscape, and the relative costs of each action. A stochastic model and accompanying methodology were developed that allows a manager to determine the optimal policy for small populations. We also provided two approximations, including a rule of thumb, for determining the optimal policy for larger metapopulations. Our method was applied to a population the greater bilby (Macrotis lagotis) that inhabits southwestern Queensland. We found that, given realistic costs for each action, protection of patches should be prioritized over patch creation for improving the persistence of the greater bilby over the next 20 years.

  Research outputs

  Ross, J.V., Sirl, D.J., Pollett, P.K. and H.P. Possingham (2008) Metapopulation persistence in a dynamic landscape: more habitat or better stewardship? Ecological Applications 18, 590-598.

Awards and Achievements

• Phil Pollett (with Hugh Possingham, The Ecology Centre, The University of Queensland) was awarded $71,346 from the Australian Centre of Excellence for Risk Analysis (ACERA) for a project titled "Strategies for managing invasive species in space: deciding whether to eradicate, contain or control" (2008-2009)