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Ecosystem functioning: a Southern and Northern Hemisphere freshwater comparison


   Cardiff School of Biosciences

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  Dr Isa-Rita Russo, Prof M Bruford  No more applications being accepted  Funded PhD Project (UK Students Only)

About the Project

Project Background: Freshwater ecosystems provide key ecosystem services but are among the most threatened globally due to pollution, eutrophication, overexploitation, land-use change and invasive species (Dudgeon et al. 2006; Glen et al. 2010; Boon and Raven 2012; Capon et al. 2013). Within aquatic ecosystems, genetic diversity supports local adaptation of populations and is therefore potentially essential in maintaining ecosystem services and resilience (Wernberg et al. 2018). Resilience can be defined as the ability of the ecosystem to maintain its initial level of functioning after a disturbance (Hodgson et al. 2015). A positive relationship between genetic diversity and ecosystem resistance/resilience has been demonstrated in various taxonomic groups including plants (Reusch et al. 2005) and animals (Lotze et al. 2011).

The goods and services derived from freshwater systems have an estimated global value of several trillion USD (Darwall et al. 2009). In southern Africa, biodiversity within inland water ecosystems is highly diverse and of great importance to livelihoods and economies. The IUCN Species Programme, South African Institute for Aquatic Biodiversity (SAIAB) and South African National Biodiversity Institute (SANBI) carried out an assessment of the status and distribution of 1,279 freshwater taxa from fish to aquatic plants. Despite this effort, freshwater diversity for southern Africa remains poorly understood (Darwall et al. 2009). One of the species (brown trout) that have been assessed in this survey will form part of the proposed project. In addition, three invertebrate species (mayflies and stoneflies) will be studied.

Brown trout (Salmo trutta) is a European species of salmonid fish. It is an apex predator in freshwater ecosystems and may influence other fish, invertebrate and plankton communities. Previous studies have shown that brown trout exhibits remarkable levels of genetic variation (Ferguson 2003). Brown trout was introduced to South Africa from Scotland in 1890 (Cambray 2003) and has thus been in South African freshwater systems for about 130 years. Studies have linked the species to the decline of indigenous fish populations due to predation and competition (Cambray 2003). On the contrary, some authors argue that the impact of brown trout on the environment is limited.

Invertebrates are integral components of freshwater food webs and perform many essential ecosystem functions such as regulating primary production, decomposition, water clarity, thermal stratification, and the cycling of nutrients (Strayer 2006).

Here the successful candidate will study two different freshwater ecosystems, focusing on one apex predator and three invertebrate species per system. We will assess genetic diversity and structure, whether reduced genetic diversity is due to bottlenecks, and more broadly what this indicates in terms of ecosystem resilience/resistance. The two freshwater ecosystems are in different hemispheres. The main focus of this PhD will be on a Southern Hemisphere ecosystem in southern Africa, because biodiversity is comparatively less well studied here.


Project Aims and Methods: A replicated experimental approach that will allow for a Southern (South Africa) vs Northern (upland Wales) Hemisphere comparison, and one where the apex predator is indigenous (in the North) versus introduced (in the South) will be followed. The project will consist of four Work Packages (WPs). In brief, WP aims are as follows: WP1 will investigate the demographic history of upland Welsh populations of brown trout (apex predator) and three macroinvertebrates. The data for this work package have previously been collected so this work package will focus on developing/optimising an analysis pipeline that can be implemented for the newly collected data from the Southern Hemisphere. WP2 will identify and assess freshwater diversity for South Africa. Freshwater diversity has already been assessed for upland Wales. In South Africa, diversity will be compared across freshwater systems with and without invasive brown trout. Genetic diversity within native and invasive brown trout populations across samples from the Northern and Southern Hemispheres will also be calculated. In WP3, the individual and ecosystem responses to stressors such as invasive species (brown trout in the Southern Hemisphere) will be studied. WP4 will infer demographic history (ABC modelling) of an apex predator and three macroinvertebrates for the Southern Hemisphere. Results from this WP will be combined with the results from WP1 to test for ecosystem resilience or resistance. Several freshwater species will be selected to represent different trophic levels (primary producers vs apex predators). 

Supervisory Team: Dr Isa-Rita Russo, Professor Michael Bruford, Professor Paulette Bloomer and Ian Rushworth

The successful candidate should demonstrate a strong academic record with expertise relevant to this project, including GIS and bioinformatics skills. Molecular ecology expertise would be ideal but is not a prerequisite. Experience with Big data is desirable. Must be able to work in the field under challenging


Funding Notes

The studentship can start on 1st July 2022 or 1st October 2022 and is for 3 years. Funding covers UK tuition fees, a maintenance stipend (£16,062 2022/23 rate). The studentship is funded by the School of Biosciences.

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