Spatial ecology and conservation of the endangered tansy beetle

Overview

Effective species conservation requires an understanding of population dynamics in space and time. Many rare species function as metapopulations, in which networks of populations exchange individuals through dispersal, allowing colonisation of empty patches and potentially rescuing small populations from local extinction. The effect of dispersal on metapopulation dynamics is especially pronounced when the habitat patch network undergoes its own dynamics. For example, when habitat patches are individual host plants of an insect, then seed dispersal will promote new patches in the metapopulation, while mortality of the host plant removes patches (potentially because of insect consumption). The overall effect of this turnover is a dynamic patch network and an increased reliance on dispersal for the species to track a moving target of habitat patches.

This studentship will focus on the tansy beetle (Chrysolina graminis). The beetle has a stronghold (meta)population on the banks of the River Ouse around York, which was thought to be its entire UK population. However, the beetle was recently rediscovered in two East Anglian fenland sites where it had been considered extinct. Because of its geographical restriction and vulnerability to major flooding, the tansy beetle is listed as endangered in the British Red Data Book and prioritised for conservation as a UK Biodiversity Action Plan species with the support of a dedicated conservation partnership – the Tansy Beetle Action Group (TBAG).

The main focus of the PhD will be on the beetle’s metapopulation dynamics in a dynamic patch network of tansy plants around York. Building on our previous work on patch occupancy and dispersal and an unprecedented >10-year TBAG survey dataset mapping thousands of tansy patches over 45 km of riverbank, the student will investigate questions such as:
1. How dynamic is the tansy patch network? What determines patch appearance and loss?
2. How does the beetle metapopulation function? What determines colonisation and local extinction?
3. What are the long-term risks of regional metapopulation extinction and how might this be minimised?

A second focus will be on better understanding the re-discovered fenland populations to inform conservation, based on knowledge gaps identified by TBAG. Depending on their interest, the student will investigate questions such as:
1. How are beetle distributions structured in the fenland sites? Are they aggregated in particular areas or on particular host plants?
2. How does performance vary on alternative host plants? The fenland populations seem to use the mint family rather than tansy but the effects of host plant choice are not known.

Methodology

To investigate metapopulation dynamics the student will contribute to the ongoing TBAG survey of tansy patches and beetle numbers around York, analyse/model these data and conduct targeted fieldwork to enhance understanding from the survey data. Depending on their interests, the student will work on some or all of the following:
1. Statistical analysis of patch network dynamics, e.g. Generalised Linear Mixed Models (GLMMs) for tansy patch appearances and disappearances using predictors such as patch size, proximity, land use, flooding and beetle density.
2. Statistical modelling of beetle occupancy dynamics, e.g. dynamic occupancy models or GLMMs predicting colonisation and local extinction. Targeted fieldwork may supplement or test inferences from the existing data, e.g. to establish distance effects on colonisation.
3. Statistical analysis of spatial synchrony in tansy and beetle dynamics, e.g. testing for effects of distance, crossing the river (a dispersal barrier), land use and flooding perturbations.
4. Development of realistic metapopulation models to estimate regional extinction risk and project impacts of future conservation and environmental change scenarios. Models could test effects of changes in grazing, patch creation, translocations between riverbanks, and/or climate change scenarios for flooding.

To better understand the ecology of the fenland populations and inform their conservation, as well as to broaden training opportunities for the student, at least one of the following activities:
1. Survey alternative host plant distributions and beetle numbers in the fenland populations, to test for spatial aggregation and local host plant/habitat preferences.
2. Rearing experiments using different host plants at the University of Stirling Controlled Environment Facility. These will test whether beetle populations differ in growth, survival and fecundity depending on host plant.

Project Timeline

Year 1

Literature review of dynamic metapopulations
Spatial analysis of York survey data and preliminary statistical analysis
Training in GLMM, occupancy models and other statistical modelling
Assist with ongoing beetle surveys in York and fenland populations

Year 2

Complete statistical modelling of patch and beetle dynamics, with field work to supplement data analyses, and submit 1-2 papers, also to be used as thesis chapters
Continue survey work and/or establish rearing experiments

Year 3

Development and simulation of metapopulation models, writing up as a paper/chapter
Analysis of fenland survey data and/or rearing experiment data, writing up as a paper/chapter

Year 3.5

Finalise papers and thesis

Training
& Skills

Key skills and expertise will be developed through the supervisory team and wider training opportunities in:
1. Spatial analysis (e.g. QGIS and R) including high performance computing clusters (HPC)
2. Advanced statistical modelling in R (e.g. occupancy models, GLMM)
3. Programming of metapopulation dynamics in R and simulation on HPC
4. Presenting complex models and results to audiences of academics and users (e.g. conservationists such as TBAG)
5. Field surveying and experimental design (including insect rearing in Controlled Environment Facilities)

References & further reading

Oxford, G. (2021) Biology and Conservation of the Tansy Beetle – 20 years on. British Wildlife 32, 411-418.
Chapman et al (2007) Modelling population redistribution in a leaf beetle: an evaluation of alternative dispersal functions. Journal of Animal Ecology 76, 36-44.
Chapman et al (2009) Process from pattern in the distribution of an endangered leaf beetle. Ecography 32, 259-268.
Bullock et al (2020) Human-mediated dispersal and disturbance shape the metapopulation dynamics of a long-lived herb. Ecology 101, e03087

Further Information

Daniel Chapman, daniel.chapman@stir.ac.uk

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