Project Description

A full project description can be found on Find a PhD. Please see below for additional information about this project:

The persistence of plant populations in fragmented landscapes is dependent on adequate gene flow via seed and pollen dispersal. The extent and consequences of variation in seed and fruit dispersal have been thoroughly explored from theoretical perspectives, and our knowledge of empirical seed dispersal kernels is expanding rapidly. However, the role of pollinators in counteracting seed dispersal limitation has been poorly explored and may be significant in habitats and landscapes where pollinator limitation represents a constraint on maintenance of genetic diversity and the persistence of plant populations. Our research has documented a trade-off among closely related coexisting tropical tree species between flower size and flower number that may represent a fundamental constraint on the boundaries of flower trait evolution (Kettle et al. 2011). In this system, small-flowered species are pollinated by relatively immobile pollinators with small body size and dispersal capacity. Therefore, although these species produce a vast number of small flowers, mean pollen dispersal distances tend to be low and a high proportion of mating events occur between related individuals, leading to high abortion rates during seed development. Related species with larger flowers generally attract larger insect pollinators that disperse over greater distances and generate much broader pollen dispersal kernels and a lower likelihood of sib-sib mating events. Therefore, for these species, the greater likelihood of successful pollination and seed maturation offsets their lower production of flowers, which equalizes reproductive output despite wide variation in flower size, pollinator size and pollen dispersal distance.

This trade-off has been identified in one study system, but the generality of these patterns and their implications for conservation of plants in fragmented landscapes are poorly known. This project will use spatially explicit demographic and foraging models (Bocedi et al. 2014, Nicholson et al. 2019) to explore the drivers underlying the evolution of flower trait variation and test the implications of these trade-offs for the maintenance of genetic diversity and population persistence in spatially heterogeneous fragmented landscapes. Do specific trait values or combinations of traits predict differences in fine-scale spatial genetic structure and the likelihood of sib-sib mating among species? How does habitat fragmentation affect pollen dispersal and maintenance of genetic diversity for species with different trait values? Are some species more tolerant of the genetic implications of habitat fragmentation than others, and how can these vulnerabilities be offset by restoration of habitat connectivity and gene flow?

Plants are dependent on movement of pollen and seeds for sustaining gene flow within and between populations, which is critical to maintenance of genetic and species diversity. However the dispersal of pollen and seeds across landscapes may be disrupted by anthropogenic disturbances, such as logging, that change the density of reproductive individuals, or create barriers to movement through habitat fragmentation. These disturbances may be particularly severe for many tropical tree populations, which have been exposed to rapid transitions in their population density and habitat structure as a consequence of recent deforestation and fragmentation. These transitions have been particularly severe in Southeast Asia, which are dominated by trees in the Dipterocarpaceae. Dipterocarps represent a high-value source of tropical timbers and logging based on extraction of these trees underpins local economies and livelihoods across the region.
Dipterocarps possess a suite of reproductive traits that induces enhanced vulnerability to loss of genetic diversity in response to reductions in population size or habitat fragmentation. They have evolved a ‘general flowering – mast fruiting’ reproductive phenology, resulting in infrequent and episodic recruitment following community-wide flowering events. They are pollinated by a wide variety of insects ranging from thrips to giant honeybees, and there is evidence that competition for pollinator services limits pollination success during these flowering events, particularly for species that produce a large number of small flowers. Importantly, pollinator body size is linked to their mobility, so mean pollen dispersal distance declines for small-flowered species pollinated by small insects. Short-distance pollen dispersal confers a greater likelihood of sib-sib mating in plants, particularly for those with inherently limited seed dispersal such as dipterocarps. Such species are characterised by a high degree of fine-scale genetic structuring within populations, and an inherent risk of inbreeding costs in response to limited pollinator mobility.
These attributes of their reproductive biology may help explain a syndrome of trade-offs linking flower size, pollination success, pollinator mobility and spatial genetic structure across multiple dipterocarp species. These attributes are shared by many other groups of angiosperms, and it is possible that similar syndromes may exist more generally in many insect-pollinated plant groups. However, this syndrome linking plant traits to population genetic structure has never been framed or tested theoretically, and its implications for the actions required to conserve different plants have not been explored.
It is our hypotheses that competition among coexisting species for pollination services drives reciprocal evolution of pollinator and plant reproductive traits, including flower size, pollinator size and pollinator mobility, leading to
• A negative trade-off between flower size and flower number across species
• A positive association between flower size and pollinator body size
• A positive association between flower size and pollination success
• A positive association between flower size and pollen dispersal distance
• A negative association between flower size and frequency of sib-sib mating
• A negative association between flower size and fine-scale population genetic structure
• Equalisation of reproductive success

Essential skills

  • Academic background in ecology, biology or conservation science
  • Quantitative or spatial modelling skills or aptitude to learn

Desirable skills

  • Field experience, not necessarily overseas

Photo by Mikey O’Brien.

Supervisors

David Burslem

Primary Supervisor:

Profile: David Burslem
Email: d.burslem@abdn.ac.uk
Institution: University of Aberdeen
Department/School: School of Biological Sciences

Paul Caplat

Secondary Supervisor:

Profile: Paul Caplat
Email: p.caplat@qub.ac.uk
Institution: Queen's University, Belfast
Department/School: School of Biological Sciences

Justin Travis

Additional Supervisor:

Profile: Justin Travis
Email: Justin.travis@abdn.ac.uk
Institution: University of Aberdeen
Department/School: School of Biological Sciences

Additional Supervisor:

Dr Chris Kettle (CASE partner: Bioversity International, Rome Headquarters) is an expert in tree genetic resources and will serve as the lead contact with the CASE partner

Dr Riina Jalonen (CASE partner: Bioversity International, Malaysia country office) is an expert in Southeast Asian forest genetics and will serve as the secondary CASE partner providing in-country support during fieldwork

References

Philipson, C.D., Cutler, M.E.J., Brodrick, P.G., Asner, G.P., Boyd, D.S., Moura Costa, P., Fiddes, J., Foody, G.M., van der Heijden, G.M.F., Ledo, A., Lincoln, P.R., Margrove, J.A., Martin, R.E., Milne, S., Pinard, M.A., Reynolds, G., Snoep, M., Tangki, H., Wai, Y.S., Wheeler, C.E. & Burslem, D.F.R.P. (2020) Active restoration accelerates the carbon recovery of human-modified tropical forests. Science, 369, 838–841. DOI: 10.1126/science.aay4490.

Tito de Morais, C., Kettle, C.J., Philipson, C.D., Maycock, C.R., Burslem, D.F.R.P., Khoo, E. & Ghazoul, J. (2020) Exploring the role of genetic diversity and relatedness in tree seedling growth and mortality: a multi-species study in a Bornean rainforest. Journal of Ecology, 108, 1174–1185. doi: 10.1111/1365-2745.13331.

Smith, J.R., Ghazoul, J., Burslem, D.F.R.P., Itoh, A., Khoo, E., Lee, S.L., Maycock, C., Nanami, S., Ng, K.K.S. & Kettle, C. (2018) Are patterns of fine-scale spatial genetic structure consistent between sites within tropical tree species? PLoSONE, 13. e0193501.

Nutt, K.S., Burslem, D.F.R.P., Maycock, C.R., Ghazoul, J., Khoo, E., Hastie, A. & Kettle, C.J. (2016) Genetic diversity affects seedling survival but not growth or seed germination in the Bornean endemic dipterocarp Parashorea tomentella. Plant Ecology and Diversity, 9, 471-481. dx.doi.org/10.1080/17550874.2016.1262923.

Tito de Morais, C., Ghazoul, J., Maycock, C.R., Bagchi, R., Burslem, D.F.R.P., Khoo, E., Itoh, A., Nanami, S., Matsuyama, A., Finger, A., Ismail, S.A. & Kettle, C.J. (2015) Understanding local patterns of genetic diversity in dipterocarps using a multi-site, multi-species approach: Implications for forest management and restoration. Forest Ecology and Management, 356, 153-165.

Smith, J.R, Bagchi, R., Ellens, J., Kettle, C.J., Burslem, D.F.R.P, Maycock, C.R., Khoo, E. & Ghazoul, J. (2015) Predicting dispersal of auto-gyrating fruit in tropical trees: a case study from the Dipterocarpaceae. Ecology and Evolution, 5, 1794–1801. doi: 10.1002/ece3.1469.

Kettle, C.J., Maycock, C.R. & Burslem, D.F.R.P. (2012) New directions in dipterocarp biology and conservation: a synthesis. Biotropica, 44, 658–660.

Kettle, C.J., Burslem, D.F.R.P. & Ghazoul, J. (2011) An unorthodox approach to forest restoration. Science, 333, 36.

Kettle, C.J., Ghazoul, J., Ashton, P., Cannon, C.H., Chong, L., Diway, B., Faridah, E., Harrison, R., Hector, A., Hollingsworth, P., Koh, L.P., Khoo, E., Kitayama, K., Kartawinata, K., Marshall, A.J., Maycock, C., Nanami, S., Paoli, G., Potts, M.D., Samsoedin, I., Sheil, D., Tan, S., Tomoaki, I., Webb, C., Yamakura, T., Burslem, D.F.R.P. (2011) Seeing the fruit for the trees in Borneo. Conservation Letters, 4, 184-191.

Kettle, C.J., Hollingsworth, P.M., Burslem, D.F.R.P., Maycock, C.R., Khoo, E. & Ghazoul, J. (2011) Determinants of fine-scale spatial genetic structure in three co-occurring rain forest canopy trees in Borneo. Perspectives in Plant Ecology, Evolution and Systematics, 13, 45-54.

Kettle, C.J., Maycock, C.R., Ghazoul, J., Hollingsworth, P.M., Khoo, E., Rahayu Sukmaria Haji Sukri & Burslem, D.F.R.P. (2011) Ecological implications of a flower size/number trade-off in tropical forest trees. PLoS ONE, 6: e16111. doi:10.1371/journal.pone.0016111.

Kettle, C.J., Ghazoul, J., Ashton, P.S., Cannon, C.H., Chong, L., Diway, B., Faridah, E., Harrison, R., Hector, A., Hollingsworth, P., Koh, L.P., Khoo, E., Kitayama, K., Kartawinata, K., Marshall, A.J., Maycock, C.R., Nanami, S., Paoli, G., Potts, M.D., Sheil, D., Tan, S., Tomoaki, I., Webb, C., Yamakura, T., Burslem, D.F.R.P. (2010) Mass fruiting in Borneo: a missed opportunity. Science, 330, 584.

Research Methods

This project will examine the evolution of reproductive traits that are critical to the persistence of plant populations in heterogeneous environments, and apply that knowledge to understanding differential vulnerability of tropical tree species to loss of genetic diversity following population fragmentation.

 

Expected Training Provision

Training will be provided in the use and development of relevant modelling platforms and the statistical approaches required for data synthesis and analyses. To parameterise and validate the models there may be opportunities for fieldwork in a tropical forest environment and collection of genomic data from plants and their pollinators. Training will be provided in preparation for fieldwork and laboratory analyses.

Impact

The project will contribute new insights into the mechanisms that generate and maintain diversity within and between tropical tree species. This is important because loss or degradation of tropical tree populations undermine efforts to protect biodiversity and sustain the ecosystem services they deliver. Multiple national and international policies and legal instruments recognise the importance of maintaining and/or restoring tree populations. One of the key drivers of tropical forest degradation is the failure of many tree species to reproduce successfully in human-modified environments, particularly where anthropogenic disturbance has reduced the density of reproductive adults and separated them in space through habitat fragmentation. Pervasive recruitment failure may arise because animal-mediated pollination becomes disrupted by the over-dispersion of adult trees or reductions in pollinator abundance. This project will provide insights into which traits confer differential vulnerability to cross-pollination among tropical trees, and therefore help to prioritize conservation efforts. It will also identify landscape configurations that might inhibit out-crossing for multiple taxa with different traits, enabling a deeper understanding of how landscape structure interacts with individual species’ traits to determine community assembly in habitat fragments.

This information is important to the design of restoration strategies for degraded and fragmented forests globally. Approaches involving tree planting require a large supply of genetically diverse and well-adapted seedlings, but planting material sourced from residual tree populations in forest fragments may instead be inbred and lacking in vigour. Similarly, reliance of natural regeneration will only be successful if new seedlings of the desired species are recruited in sufficient numbers, otherwise these is a risk that sites will become dominated by pioneer trees and lianas. Greater knowledge of the traits that confer successful out-crossing in fragmented populations, and the drivers of loss of genetic diversity, will help inform decision making over the distribution of restoration effort at landscape scales.

Proposed Timetable

The timetable for the research would be developed by discussion between the supervisors and the successful candidate during the early stages of the project, to ensure that objectives and milestones are realistic whilst also reflecting the aspirations of the candidate in terms of focus and training requirements. Therefore the following timetable should be regarded as indicative only.

Year 1
The first six months will be devoted to induction, training and development of a research proposal, which will include exploration of appropriate modelling platforms. This phase will include intensive reading, preparation of a literature review and attending compulsory generic training modules. A final task will be preparation for fieldwork, which will involve submission of all necessary permit applications, import licenses and risk assessments.

The second six months would be an opportunity to conduct the first field season for sample collection, and completion of the nine-month assessment progression requirement.

Year 2
The first six months will focus on molecular analysis of samples collected in Year 1, followed by bioinformatic analyses of the data. Where necessary, these activities will be preceded by training. Presentation of a poster at the Annual Meeting of the British Ecological Society would be a reasonable target.

The second six months will focus on further model development and writing a paper based on the preceding work, followed by a second field season to fill gaps in sample coverage.

Year 3
The main task for the third year will be to complete all molecular and bioinformatics analyses, implement model runs and then initiate thesis preparation. An internship with Bioversity International would be possible during this period, especially in the context of outreach and dissemination activities. Oral presentation at a conference would be expected.

Year 4 (six months)
The entire focus will be on completing the thesis chapters and associated papers.

QUADRAT Themes

  • biodiversity
  • environmental-management

Partners

CASE Partner: Bioversity International & Bioversity International (Malaysia country office)

Bioversity International acts all tropical regions to develop solutions to the loss of genetic diversity among wild trees and crops, particularly in settings where widespread habitat loss and fragmentation have reduced the density of adult trees of reproductive size. This project has been co-developed with Bioversity International scientists and will explicitly explore solutions to the problem of low genetic diversity in the seed supply chain that limits the expansion of tree cover on agricultural land in the tropics.

Overseas fieldwork would be conducted in partnership with local organisations with whom we have long-standing research collaborations, such as the Southeast Asia Rainforest Research Partnership, government departments and non-governmental organisations. These linkages are important for ensuring that access and research permit applications are supported, and for local dissemination of our results.

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