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“The History and Future of Island Conservation in a Snail Shell”

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“The History and Future of Island Conservation in a Snail Shell” “The History And Future Of Island Conservation In A Snail Shell” “Utilising historically formed baselines and extinction risk analysis within island ecosystems to inform risk assessment and future Partula reintroduction planning” By Sam Aberdeen September 2013 “A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science and the Diploma of Imperial College London” Declaration of own work I declare that this thesis “The history and future of island conservation in a snail shell” is entirely my own work and that where material could be construed as the work of others, it is fully cited and referenced and or with acknowledgement given. Signature: Name of Student: Sam Aberdeen Name of Supervisor: Dr Ben Collen Name of Supervisor: Dr John Fa - 1 - S. Aberdeen CONTENTS I. Acronyms and Definitions………………………………………………………………………………………………………………..4 II. Abstract (With word count)…………………………………………………………………………………………………..…………5 III. Acknowledgements……………………………………………………………………………………………………………….…………5 1. INTRODUCTION………………………………………………………………………………………………………………............………6 1.1 Isolation and extinction……………………………………………………………………………..………………...……………...6 1.2 Creating an island baseline to analyse extinction risk…………………………………………………….……………..7 1.3 Population Viability Analysis (PVA) in estimating extinction and management risk………………….……9 1.4 Partula as a model island taxon…………………………………………………………………………………………….…....11 1.5 Developing PVA model to inform Partulid reintroductions……………………….…………..…….……….……..12 2. SUMMARY………………………………………………………………………………………………………………………….…………....14 3. METHODS…………………………………………………………………………………………………………………………………………15 3.1 Data collection…………………………………………………………………………………………………..………………….…….15 3.1.1 For Red List Assessments……………………………………………………………………………..…………………15 3.1.2 Reasons for decline………………………………………………………………………………………………..….……17 3.1.3 For PVA……………………………………………………………………………………………………………………...…..18 3.2 Analysis…………………………………………………………………………………………..…………………………………..….…..19 3.2.1 Reasons for decline – modelling Partulid range reduction ………………………………..………...…19 3.2.2 Calculating the RLI……………………………………………………………………………………………...........….20 3.2.3 RAMAS Meta-population Models using Stage Matrix………………………………….……………….…21 4. RESULTS………………………………………………………………………………………………………………….………………………..24 4.1 How has extinction risk varied for Partula since 1975?...................................................................24 4.2 What are the factors causing the observed decline and how do the factors interact?...................25 4.3 Can the current re-introduction and management strategies provide a secure long term option for in-situ Partulid populations?.......................................................................................................26 5. DISCUSSION………………………………………………………………………………………………………………………………………33 5.1 How has extinction risk varied for Partula since 1975?...................................................................33 5.1.1 The island baseline formation and populations pre 1970……………………………..…………….....33 5.2 What are the factors causing the observed decline and how do the factors interact?...................34 5.2.1 Agricultural expansion…………………………………………………………………………………………..……....34 5.2.2 Invasive species………………………………………………………………………………………………............…..34 5.2.3 Human invasive interaction………………………………………………………………………………………...….35 5.2.4 Key elements of Partulid extinction……………………………………………………………………………..…36 5.3 Can the current re-introduction and management strategies provide a secure long term option for in-situ Partulid populations?.......................................................................................................37 5.3.1 The state of the islands…………………………………………………………………………………………………..37 5.3.2 Predation on the Society Islands…………………………………………………………………………………….37 5.3.3 Predation in classic reserves…………………………………………………………………………………………..37 5.3.4 Arboreal reserves and predation………………………….…………………………………………………………37 5.3.5 Comparative outcomes for models…………………………………………………………………………………39 5.3.6 Carrying capacity In all reserves…………………………………….…………………………………………….…40 5.3.7 Density dependence…………………………………………………………………………………………………….…40 5.3.8 Getting the first population right……………………………………………………..…………………………….41 6. CONCLUSIONS………………………………………………………………………………………………………………………………….41 7. REFERENCES…………………………………………………………………………………………………………………..………………..45 8. APPENDICIES…………………………………………………………………………………………………………………………………….49 - 2 - S. Aberdeen Appendix 1 – Partulid extent of occurrence maps and E.rosea dispersal maps. Appendix 2 – Modelled Partulid Red List assessments due to E.rosea range expansion. Appendix 3 – Descriptions of range and biology of Partula and Samoana species from early literature. Appendix 4 – Political and social context of land use change in French Polynesia. Appendix 5 – PVA model summaries. Appendix 6 – Parameters for modelled populations in questions 3a and 3b. Appendix 7 – Euglandina survey data supplied by Dr Trevor Coote . Appendix 8 – Land use map and Euglandina life history table from Gerlach (1992). Appendix 9 – IUCN Red List Assessments for Partula as assessed by Dr Trevor Coote. Appendix 10 – R code for multiple regression analysis of census data. - 3 - S. Aberdeen I. ACRONYMS AND DEFINITIONS EOO - Extent Of Occurrence RLI - Red List Index PVA - Population Viability Analysis IUCN - International Union for the Conservation of Nature CEPF - Critical Ecosystem Partnership Fund GDEM - Global Digital Elevation Model QGIS - Quantum Geographic Information System PSMS - Partula Species Management System ZSL, B.U.G.S. Department - Zoological Society London, Biodiversity Underpinning Global Survival Department. Quazi Extinction - A measure of extinction risk based on the number of population replications that result in extinction as a proportion of the total number of replications. Trajectory Summary - A measure of the population size achieved throughout the timeframe modelled. - 4 - S. Aberdeen II. ABSTRACT Over the course of the last 12,000 years island ecosystems have been confronted by an increasing suite of threats. Direct human persecution, urban and agricultural expansion, invasive species and increasingly more turbulent environmental conditions, mean that even the most abundant and ecologically robust species are being put at risk of extinction. New waves of island extinctions are continuing to occur world- wide, and although impacts on vertebrates tend to be most widely studied, increasingly, the building blocks of ecosystems - invertebrate and plant species - are being affected. There is an urgent need to determine how recent changes in island species relate to historic baselines and how present levels of extinction risk can be better managed. Here I create an index of changing extinction risk over a four decade period for Society island snails of the genus Partula. I use this as a baseline against which to evaluate change in extinction risk using the Red List Index method, and examine the causes and effects of different factors on island species extinction risk. Using PVA, I then evaluate how more detailed information on the pressures that have contributed to high extinction risk, can be used to identify future management options that reduce extinction risk for this taxonomic group. I find that interactions between humans and invasive species post the first island invasion, can have a great effect on the rate of spread and the final impact of the introduction. Further management strategies designed to reduce risk to the entire island populations, also promise viable outcomes because of changes in invasive predation pressure. However, the numbers of animals within starter populations are key to reducing risk. Word Count: 14,878 III. ACKNOWLEDGEMENTS I must firstly acknowledge the input of my supervisors Dr Ben Collen, Dr Monika Bohm and Dr John Fa of University College London , Zoological Society London and Jersey Zoo respectively for their support and tutelage throughout this study. I must also thank the Biodiversity monitoring specialist group at UCL for additional funding to enable the PVA element of this study. I have been dependant on the support and advice given from the entirety of the Pacific Islands Snail Conservation group, with particular reference to Dr Trevor Coote who has answered many Partulid based emails, and the ZSL BUGS department including Don Mcfarlane, Paul Pearce Kelly and David Clarke who enabled the access of the PSMS data base for this study. Dr Justin Gerlach has throughout this study analysed carefully the placement of each Partulid population and discussed the many pitfalls and possibilities in the further study of Partula. The Natural History Museum London, for access to their collections as well as the other museum sources listed in the text. Finally this is dedicated to the unbending support of my parents and the enthusiastic support of my wife who is continuing to enjoy every second of my conchological exploits. - 5 - S. Aberdeen 1. INTRODUCTION 1.1 Isolation and extinction Islands have been a focal point for extinction events for over one thousand years. Monotypic geology, restricted size and geographic isolation create unique evolutionary environments that can be extremely vulnerable to external interference or rapid internal change. This vulnerability is likely to account for a significant proportion of the first waves of extinction during the Holocene (Steffen, Crutzen and McNeill, 2007) as Homo sapiens began to move into isolated regions, placing new pressures
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