Land use change and trophic links between aquatic and terrestrial ecosystems

Land use change is considered to be the greatest cause of species loss globally. Its effects have been widely reported in terms of reduced diversity, but there has been much less progress in understanding how it affects ecosystem processes and resilience to other disturbances (e.g. climate change, alien species). One particular area of weakness is how land use change affects interactions between different ecosystems (e.g. through movements of organisms and resources). Such interactions can have large effects via cross-ecosystem subsidies or trophic cascades, which in turn are likely to affect within-ecosystem processes and community resilience.

This PhD aims to address this gap by looking at food web structure and aquatic-terrestrial links across a gradient of increasing agricultural intensity. Agricultural intensification is one of the most widespread forms of land use change, with activities such as increased livestock densities and more frequent fertiliser and pesticide applications having well documented effects on biodiversity. This project will focus on farmland streams and the adjacent terrestrial habitats, as these are major sources of diversity in the farmland landscape, support key ecosystem services (e.g. biocontrol, pollination) and riparian management is a focus for reducing land use and climate change impacts on freshwaters. Despite this, relatively few studies have spanned aquatic and terrestrial systems. Combining field sampling, recently developed molecular dietary analysis and food web modelling, the PhD will aim to:

Characterise the food webs and prey choices of major consumers (e.g. carabid beetles, predatory stoneflies, river birds) in the streams and neighbouring terrestrial habitats.

Assess how the strength of cross-ecosystem interactions changes with increasing land use intensity

Develop food web models based on the empirical data to assess community robustness to: i) changes in the strength of aquatic-terrestrial linkages, and ii) wider environmental change (e.g. climate change). This will address important questions about how land use intensification affects characteristics such as robustness and food web persistence (e.g. Gilarranz et al. 2016, Nature Commun. 7, 10737)

The overall aim is to provide greater insight into how ecosystems respond to intensification and what this means for longer term sustainability of farmland biodiversity in a changing environment.

Extensive training in all aspects of the project will be provided by a combination of the supervisory team and formal courses, tailored to the needs of the student and the project, and including the requisite data analysis, lab and fieldwork techniques. The student will be based in Cardiff, with regular visits to Bristol throughout the PhD, including longer periods for training in key areas (e.g. network analyses).