School of Life Sciences

Dr Gemma Gerber.

Study of Estuarine Ecosystem Modelling Earns PhD

Dr Gemma Gerber secured a PhD in Biological Sciences for her thesis titled: Ecosystem Indicator Assessment: Incorporating Uncertainty into Estuarine Ecosystem Models.

Geber’s focus on estuarine ecosystems was especially relevant given the growing consensus amongst academics about systems-level research.

‘Estuaries are the habitats where rivers meet the sea,’ said Gerber. ‘They are enormously productive and provide immeasurable ecosystem goods and services. They are also some of the most threatened habitats in the world in terms of climate change and human activities.’

In South Africa, drought is a significant threat to estuarine biodiversity and ecosystem function. ‘While we know how drought can affect aspects of estuaries through water chemistry, primary producers and invertebrates, there is very little information regarding South Africa on how such changes are reflected in the overall ecosystem function,’ she said.

To investigate estuarine ecosystem function under drought, Gerber modelled estuarine food webs of two-case study subtropical estuaries which showed what was in the system and how they interacted.

She then analysed the food webs with existing algorithms to quantify emergent ecosystem function, such as carbon cycling, which otherwise cannot be investigated by looking at isolated ecosystem components.

‘While my work was not the first to characterise South African estuarine ecosystem function, it was the first to characterise the uncertainty of ecosystem function,’ said Gerber.

To improve model estimations of “reality”, Gerber explained that data variability from field measurements could be incorporated into the model outputs. However, there were several practical challenges with this approach, including fragmented methods and a lack of robust model evaluation tools.

‘To address the practical challenges, I developed an R (software) package, autoLIMR, to facilitate a structured and streamlined approach to food web modelling and incorporating real-world data variability in food web model outputs,’ she said.

Her research is relevant to modellers who would like a “one-stop shop” for food web modelling software within R programming.

Gerber said she was motivated by her curiosity as to how organisms interact with one another. ‘Also, I was interested in the methodological aspects of ecosystem modelling and since there was no existing streamlined approach, I found myself becoming quite frustrated. This inspired me to write my own code to fix the problems I was having. This was the basis for what is now R package autoLIMR, which has since been extended to apply to almost any ecological network problem.’

Gerber’s research is significant as her methodology extensions solve some of the practical challenges of food web modelling, and thereby increase the use of this methodology to characterise ecosystem function.

‘The specific South African estuarine ecosystem function assessments are novel, and provide a systems-level perspective to the effects of drought on estuaries,’ she explained.

Gerber – currently a research scholar in the Biodiversity, Ecology and Conservation Research Group at the International Institute for Applied Systems Analysis (IIASA) in Laxenburg, Austria – says she would love to continue systems-focused research. ‘As part of the EU-funded “Assessing Climate Change in the European Union” project I look at the impacts of projected climate change and land use on biodiversity and ecosystem services in the EU, and potential management-related cost estimates,’ she said.

‘One day when I return home, I would like to apply this knowledge within the South African context to get more clarity on the connections between climate change and human activities on South African ecosystem service provision.’

Gerber thanked her supervisor Professor Ursula Scharler as well as her family and friends for their support.

‘Gemma was certainly one of the best students I’ve ever had the pleasure of supervising,’ said Scharler.

Words: Sally Frost

Photograph: Supplied