loading...

Available PhD projects 

Groundwater food webs

Contact: Anne RobertsonA.Robertson@roehampton.ac.uk

Groundwaters are important sources of potable water and additionally contain a unique assemblage of organisms some of whom are only found in this environment (Robertson et al. 2009). Groundwater animals are likely to play a role in altering groundwater microbial biofilms by grazing and bioturbation. These biofilms are known to be critical in the processing of organic carbon and in the moderation of nitrogen chemistry. Thus, groundwater assemblages may influence contaminant degradation and amelioration in aquifers and thereby provide an important ecosystem service. The ecology of groundwaters is still poorly understood, for example, we know relatively little about food webs in these habitats. Photosynthesis does not occur in these permanently dark environments; the base of the food web is dissolved organic carbon which is usually found in very low concentrations and is assumed to derive from the surface. This project will examine groundwater assemblages and food webs (from microbial biofilms to macro-Crustacea) in a variety of aquifers across a continuum of dissolved organic carbon concentrations. The project will also incorporate laboratory experiments designed to assess the impact of groundwater meio- and macrofauna on microbial biofilms.

Applicants will have a solid background in biology and fieldwork, and, ideally, some experience in microbiology.

Background literature: Robertson AL, Smith JWN, Johns T & Proudlove GS (2009) The distribution and diversity of stygobites in Great Britain: an analysis to inform groundwater management. Quarterly Journal of Engineering Geology and Hydrogeology. 42: 359-368.

groundwater food

 

Habitat complexity and feeding interactions

Contact: Julia Reiss, Julia.Reiss@roehampton.ac.uk and Anne Robertson, A.Robertson@roehampton.ac.uk

Feeding interactions depend on the densities of predator and prey. Moreover, the size of the food might be an important aspect of whether a food item is chosen or not, as larger prey might represent an energetically more rewarding food source. However, other abiotic/biotic factors will also be critical in whether a feeding link is expressed or not. Studies on freshwater pelagic systems have shown that the eutrophic status of the ecosystem can determine how strongly feeding links are expressed (Burns & Schallenberg, 2001). In the benthos, the structure of the environment might be another important factor influencing feeding interactions. The complexity of the habitat is believed to influence population densities, body size distributions and species richness of invertebrates (Gee & Warwick, 1994: Jeffries, 1993; Morse et al., 1985; Taniguchi & Tokeshi, 2004). Moreover, habitat complexity might directly influence the structure of the benthic food web by giving refuge against predation (Crowder & Cooper, 1982).

In this project we will test how habitat complexity influences feeding interactions between predators and prey (i.e. functional response curves). We will test a range of herbivores and predators (meiofaunal and macrofaunal size) on their preferred diet in feeding microcosms that vary in terms of habitat complexity. These experiments will be laboratory set-ups in a temperature and light controlled environment. We will mainly use organisms that we have previously identified as important components of "the small sized" food web such as meiofauna (Dineen & Robertson 2010; Reiss & Schmid-Araya 2011) and their predators.

Background literature: Papers by the group of Ulrich Brose
Dineen G., & A.L. Robertson 2010. Subtle top-down control of a freshwater meiofaunal assemblage by juvenile fish predation. Freshwater Biology 55: 1818–183
Reiss, J. and J. M. Schmid-Araya. 2011. Feeding response of a benthic copepod to ciliate prey type, prey concentration and habitat complexity. Freshwater Biology 56:1519-1530.

 

Temperature adaptation and its ecological implications

Contact: Enrico Rezende, Julia Reiss, Julia.Reiss@roehampton.ac.uk and Lewis Halsey, l.halsey@roehampton.ac.uk

Thermal adaptation is receiving increasing attention given its potential association with species distribution and responses to climate change. However, empirical observations and theoretical analyses show that critical thermal limits are highly dependent on the methodological context, raising doubts regarding the adequacy and validity of different estimates of thermal tolerance for comparative purposes and extrapolations to natural settings. The absence of a formal theoretical framework surrounds much of the debate in the literature on the genetic and physiological basis of thermal tolerance, as well as its ecological and evolutionary repercussions (Rezende et al. 2011; Santos et al. 2011).

Our goal in this project is to fill this conceptual gap, integrating theoretical and empirical analyses to ultimately predict, based on thermal tolerance estimates measured in the laboratory, how thermal regimes in the field might impact organism survival and distribution. We are interested in tackling these issues by studying a range of species, focusing primarily on aquatic and terrestrial invertebrates, to consider issues such as population differences in thermal tolerance, short-term thermal adaptation over lab-cultured generations, and inter-specific comparisons. Ideas are welcome.

References: Rezende EL, M Tejedo & M Santos (2011) Estimating the adaptive potential of critical thermal limits: methodological problems and evolutionary implications. Funct Ecol 25:111-121. Santos M, LE Castañeda & EL Rezende (2011) Making sense of heat tolerance estimates in ectotherms: lessons from Drosophila. Funct Ecol 25: 1169-1180.

temperature image

 

Biodiversity of microscopic organisms drives multiple ecosystem processes

Contact: Julia Reiss, Julia.Reiss@roehampton.ac.uk

My study organisms are mainly free-living, aquatic protists (single celled organisms) and very small multicellular animals, such as meiofauna. They are extremely abundant in aquatic habitats and they play a key role in numerous ecosystem processes. Assessing their ecological roles is needed to understand natural systems in their own right, but their study can also be used to inform and test general ecological theories, such as the relationship between biodiversity and ecosystem functioning (B-EF).

The high rates at which species are being lost from ecosystems on a global scale have stimulated interest in determining how biodiversity loss alters ecological processes that are vital to the functioning of ecosystems. Several hypotheses have been put forward to explain B-EF relationships and many of them propose that high biodiversity sustains ecosystem functioning better than low biodiversity. For example, high biodiversity has been shown to improve rates of decomposition of organic matter in aquatic systems.However, laboratory experiments addressing this point often remain inconclusive, possibly because a wider range of organisms has to be used in these experiments than has been the case to date.

Further, multiple ecosystem processes have to be measured (most studies measure one or two). Addressing both points would simulate natural diversity and hence show the "real" impact that diversity has on ecosystem functioning (Reiss et al. 2009).

My current research is now directed towards addressing realistic B-EF relationships using microscopic organisms (e.g. Reiss et al. 2010). I am interested in experiments that manipulate species richness of very different aquatic organisms (protists, small metazoans and larger fauna [such as insect larvae, small freshwater crustaceans]) in the laboratory and measure multiple processes as response variables.

These experiments would possibly demonstrate that species richness effects become more obvious when multiple ecosystem processes are taken into account. My aim is to further show that microscopic organisms drive multiple ecosystem processes in aquatic habitats.

For these experiments, I am looking for a person who has a solid background in ecology, is familiar with B-EF theories and ideally has taxonomic skills.

References: Reiss, J., Bridle, J. R., Montoya, J. M. & Woodward, G. (2009) Emerging horizons in biodiversity and ecosystem functioning research. Trends in Ecology & Evolution, 24, 505-514.

Reiss, J., Bailey, R. A., Cassio, F., Woodward, G. & Pascoal, C. (2010) Assessing the contribution of micro-organisms and macrofauna to biodiversity-ecosystem functioning relationships in freshwater microcosms. Advances in Ecological Research, 43, 151-177.

 

Allometric scaling relationships: are they the same for unicellular and multicellular eukaryotes?

Contact: Julia Reiss, Julia.Reiss@roehampton.ac.uk

In the last two decades, Ecology has received much attention among the sciences because of global change (e.g. climate change, species loss etc.). There is now a need for Ecology to be a theoretical and predictive science that shows the fundamental laws that underlie the interactions of organisms and their response to the environment.

I am interested in addressing ecological theory as put forward by the Metabolic Theory of Ecology (MTE) which aims to link body size and metabolic rates of individuals with higher level ecological patterns. In brief, this theory proposes that there are ecological laws just like the laws of physics. The key "variable" in this theory is body size. The MTE proposes that body size and metabolism of all organisms underlie the same simple power law with the same scaling exponent. It also proposes that body mass and population characteristics are connected to body mass. For example, body mass and population abundance scale with a power law, with the same exponent.

In a recent publication (Reiss et al. 2010) my co-authors and I showed that there might be difference in how body mass of unicellular and multicellular species scales with their abundances. I am interested in building on these findings with a more rigorous analysis of existing (unpublished and published) data. For this project, I am looking for a researcher who has a background in both ecology and mathematics/modelling.

Reference: Reiss, J., Forster, J., Hirst, A., Pascoal, C. & Stewart, R. (2010) When microscopic organisms inform general ecological theory. Advances in Ecological Research, 43, 45-85