Wayne Dawson (PhD)
Title: What determines species invasiveness? Testing traits with tropical trees.
Supervisors:
Dr. Phil Hulme, Centre for Ecology and Hydrology, Banchory, Scotland.
Dr. David Burslem, University of Aberdeen, Aberdeen, Scotland.
Introduction: Understanding why certain introduced plant species become invasive while others fail is a fundamental component of invasion risk assessment. To date, the search for key life history traits has been inconclusive and new evidence highlights the greater importance of extrinsic factors such as species origin and the frequency of introduction. In addition invasive traits are likely to be habitat dependent and an urgent need exists to undertake experimental rather than correlative studies of invasion success within specific habitats.
Hypotheses: Any advance in determining invasiveness will need to test the following hypotheses:
- Invasion success is a function of local population growth (r) and dispersal efficiency (D)
- Higher introduction frequency (propagule pressure) will facilitate invasion where r is limiting
- Wider spatial distribution of introductions will facilitate invasion where D is limiting
- For species where neither r nor D is limiting propagule pressure will be less important
- Trade-offs among life-history traits will determine several comparable invasion strategies
Hypotheses can only be tested by using a wide range of species over large spatio-temporal scales.
Approach: The Amani Botanical Garden (ABG) in the East Usambara Mountains (Tanzania) provides a unique opportunity to test these hypotheses. Between 1902 and 1914 about 200 ha, of the total area of 350 ha, were developed as trial plantations including close to 1,000 different indigenous and exotic species from similar ecological zones in the tropics (mainly trees, palms, and woody shrubs). These plantations (>1 plantation for many species) now form the ABG, one of the largest botanical gardens in Africa (see www.easternarc.org). Detailed inventories of the establishment and performance of the plantations were undertaken in 1934, 1960, 1980 and 1997 (data available from RBG Kew). The ABG sits within montane and lowland tropical rainforest of global importance yet a significant number of non-native species have spread into the forest from the ABG including several of the most pernicious invasive tropical plants. Due to the international significance of this global biodiversity hotspot, much of the neighbouring forest has been systematically surveyed and data are available on the distribution of many alien species. Integrating these two datasets will provide a foundation for assessing the relative success of introduced species.
Field studies will:
a) generate an updated inventory of plantations recording detailed data on performance and life-history;
b) quantify dispersal success by estimating the spatial distribution and approximate age of recruits in neighbouring forest;
c) characterise invaded habitats e.g. montane/lowland, gap/edge etc. to determine how habitat acts as a filter on species traits.
The large number of species will require a hierarchical approach where increasing detail is drawn from a representative sub-sample.
Analysis: Analyses will derive a quantitative invasion index against which life-history traits, phylogeny, propagule pressure, origin and habitat influences will be assessed. Data will be validated by examining correspondence between the quantitative invasion index and published data/checklists on the history of invasion/establishment of these species in other tropical regions. Quantitative data can be generated easily from floristic records of the abundance of the species on tropical islands.
Outcomes: This study presents a unique opportunity to generate groundbreaking results in a priority area for global biodiversity research. Not only will it provide essential information for the assessment of invasion risk but it will also further the understanding of biological invasions beyond simple case studies or correlative analyses. Although the greatest threats of invasive species are faced in the tropics the vast majority of studies on species invasiveness and risk assessment are undertaken in temperate biomes, this study will address this imbalance. The studentship will benefit from a recently funded Darwin Initiative Award (DIA) "Combating Invasive Alien Plants Threatening The East Usambara Mountains, Tanzania."
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John Richard (MSc)
Title: Status of the Panama rubber (Castilla elastica) in Amani Nature Reserve: Spread and Management options.
Supervisors:
S. Madoffe, Department of Forest Biology, Sokoine University of Agriculture, Tanzania.
Dr. Phil Hulme, Centre for Ecology and Hydrology, Banchory, Scotland.
Overall objective
The overall objective of this particular study is to assess the status of the Panama rubber (Castilla elastica) in Amani Nature Reserve, the magnitude of its spread and recommend appropriate management options.
Specific Objectives
• To identify potential pollinators of Castilla elastica in Amani Nature Reserve
• To assess the population of Castilla elastica in undisturbed, mild-disturbed and heavily disturbed forests/areas of Amani Nature Reserve.
• To recommend management options for controlling the spread of Castilla elastica
Hypotheses
Null hypothesis: Castilla elastica is not a threat to the ecosystem of Amani Nature Reserve.
Alternative hypothesis: Castilla elastica is a threat to the ecosystem of Amani Nature Reserve
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Ezekiel Edward (MSc)
Title: Population status and spread of Cordia alliodora in Amani Nature Reserve, Tanzania
Supervisors:
Prof. Munishi P. K. T, Department of Forest Biology, Sokoine University of Agriculture, Tanzania.
Dr. Phil Hulme, Centre for Ecology and Hydrology, Banchory, Scotland.
General objective
To assess the population status and spread of Cordia alliodora, in Amani Nature Reserve, Tanzania.
Specific objectives
• To assess the quantity of C. alliodora in Amani Nature Reserve in relation to other species
• To assess and map the distribution of C. alliodora in Amani Nature Reserve
• To assess the effects of C. alliodora on regeneration of indigenous species in Amani Nature Reserve
• To suggest proper management option for monitoring of C. alliodora in Amani Nature Reserve
Hypotheses
Ho: The population of Cordia alliodora have no significant effect on other plant species in Amani Nature Reserve
Ha: The population of Cordia alliodora have significant effect on other plant species in Amani Nature Reserve
Study questions
The study will be guided by the following questions
i) What is the quantity of Cordia alliodora in Amani Nature Reserve?
ii) What is the distribution status of Cordia alliodora in Amani Nature Reserve?
iii) What is the effect of Cordia alliodora on regeneration of native species in Amani Nature Reserve?
iv) What are the best management options for monitoring spread of Cordia alliodora in Amani Nature Reserve?
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