Exploring the links between invasive plants, capybara and disease vectors in São Paulo State, Brazil

Overview

Plant invasions can have major ecological impacts on the systems they colonise, and these impacts can be indirect, mediated through the interactions between resident species and invasive plants. In Sao Paulo State, Brazil, there are multiple invasive plant species that can provide food and habitat for the world’s largest rodent, the capybara (Hydrochoerus hydrochaeris). As a result, the presence of invasive plants in a landscape could have an impact on the spatial distribution and prevalence of capybara. This potential effect is important, because capybara are an important reservoir for bacteria (Rickettsia), which cause Rocky Mountain Spotted Fever in people when they are bitten by disease vectors (ticks). Thus, invasive plants may indirectly increase human health risks in invaded landscapes. However, the strength of these links between plants, capybara and disease-carrying ticks remain unexplored.

This project will explore and quantify the strength of evidence for proposed interactions within this plant-mammal-disease vector system, using a combination of camera trap surveys, habitat surveys and experiments to assess tick habitat preference, and modelling of invasive plant species distributions in São Paulo State, Brazil. This PhD project will feed into a collaborative project involving ecologists at Durham University, the University of São Paulo, and the Federal University of São Carlos.

Methodology

The project consists of three components: a camera-trapping survey, a habitat survey and a manipulative experiment involving invader removal.

Camera-trap survey: Camera traps will be deployed in paired locations that have been invaded or not by invasive white ginger (Hedychium coronarium), across both the dry and wet seasons. The images obtained will be processed and analysed to identify presence of capybara. These data will then be used in occupancy modelling to establish the probability of capybara presence while accounting for imperfect detection.

Habitat survey and manipulative experiment: Carbon dioxide traps will be deployed in paired invaded and uninvaded habitats, to capture and quantify tick abundance in different seasons. These data will be coupled with data on temperature and relative humidity captured using environmental sensors, to assess how environmental conditions vary among habitats and affect tick success.

Manipulative invader removal experiment: Open experimental plots will be established which will involve either removing standing vegetation in invaded and uninvaded habitats, or leaving vegetation intact. Camera traps will be deployed to establish the effect of vegetation removal on capybara presence. In addition, surveys of tick abundance will establish how invasion status and vegetation removal affect tick abundance.

Project Timeline

Year 1

First 6 months: Initial training; planning of fieldwork (selection of field sites, fieldwork protocols); initiate first field season [camera-trap surveys, habitat surveys]

Second 6 months: Complete first field season; begin processing images and data.

Year 2

First 6 months: complete image and data processing from first field season; data analysis

Second 6 months: write-up of first field season; Plan second field season [invader removal experiment].

Year 3

First 6 months: second field season- set up experiment and arrange data collection with collaborators

Second 6 months: Data processing and analysis. 2nd field season write-up.

Year 3.5

Complete PhD thesis write-up

Training
& Skills

You will gain a unique skills-set combining field-based and experimental methods with advanced ecological modelling and statistical analysis. You will obtain skills in camera trap surveys and downstream image analysis and data processing. You will learn how to use occupancy models, and mixed modelling, all within the R environment.

You will also gain valuable experience in designing and conducting manipulative experiments, and skills in invertebrate taxonomy and sampling. You will also benefit from being involved in a broader ongoing research project with Brazilian collaborators, focussed on this invasive plant-capybara-disease vector study system. Finally, you will benefit from regular contact with and support from postgraduates, postdocs and academic staff within Durham University’s Conservation Ecology Group.

Dr Wayne Dawson (Durham) will be the primary supervisor, providing day-to-day project guidance, advice in planning fieldwork activities and post-fieldwork data analysis and write-up. Dr Dawson is an expert in the field of invasion ecology, and leads an existing NERC/FAPESP funded project on this study system (NE/W003945/1- ‘Revealing an invasive plant-mammal-disease vector system in São Paulo State, Brazil’)

Dr Philip Stephens (Durham) will be a co-supervisor, and will provide expertise in camera-trapping surveys and ecological modelling. Dr Stephens works primarily on mammal and population ecology, and has several PhD project students using similar approaches to those planned for this PhD project.

Dr Mark Whittingham (Newcastle) will be a third supervisor, with expertise in statistical modelling, and foraging and behavioural ecology.

The PhD candidate will obtain addition training and support from our Brazilian collaborators: Prof. Vania Pivello and Prof. Marcelo Labruna (University of São Paulo), and Prof. Dalva Matos (Federal University of São Carlos).

References & further reading

Dantas-Torres et al (2021). Seasonal dynamics and rickettsial infection in free-living Amblyomma dubitatum in the Atlantic forest biome in north-eastern Brazil. Acta Tropica 217: 105854.

Lopes et al. (2021). Human-modified landscapes alter home range and movement patterns of capybaras. Journal of Mammalogy 102: 319-332.

Stewart et al (2021). Impacts of invasive plants on animal behaviour. Ecology Letters 24: 891-907.

Further Information

Dr Wayne Dawson: wayne.dawson@durham.ac.uk. Tel: +441913341308

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