PhD Code: MARES_11_04:
Mobility
- Host institute 1: P1 - Ghent University
- Host institute 2: P6 - Stichting Koninklijk Nederlands Instituut voor Zeeonderzoek (NIOZ)
- T2 - Understanding biodiversity effects on the functioning of marine ecosystems
- Colin Janssen / Marleen De Troch
- Jean-Marc Guarini
- F. Delaender (Laboratory of Environmental Toxicology and Aquatic Ecology) K. Sabbe (Protistology & Aqautic Ecology); NIOO-CEME: K. Soetaert
Subject description
Conceptual framework
The recognition, in the early 90’s, that biodiversity plays a key role in controlling processes that are essential for the functioning of ecosystems, has led to the emergence of a new field of research known as biodiversity (B) and ecosystem functioning (EF). However, many key BEF questions remain as yet unresolved. One of the main sources of uncertainty in predicting B effects on EF relates to the fact that most BEF experiments do not consider the environmental complexity within which BEF relations take place. More specifically, they do not fully consider (a) the direct effects of anthropogenic stressors on the same EFs that B influences, and (b) trophic interactions that determine species-specific and context-dependent aspects of food web structure (Duffy et al. 2007, Hillebrand et al., 2009).
Anthropogenic stressors are the driving force behind the global decrease in biodiversity (Jackson, 2010; Lotze et al., 2006). However, most BEF studies to date do not explicitly include anthropogenic stressors in the experimental design (but see Mulder et al 2001; Reusch et al 2005). Instead of having increasing stressor levels create a gradient of B levels - as is the case in nature - researchers themselves created a B gradient by randomly composing multi-species assemblages with increasing B levels (Balvanera et al.,2006).
The dynamic interplay of species-specific functional traits and rates, species diversity (i.e. community composition) and trophic interactions makes it difficult to mechanistically explain observed BEF relationships in stressed ecosystems. Although measuring species diversity is relatively straightforward, it is practically infeasible to quantify as many functional rates and trophic interactions as is needed to understand the dynamic phenomena described above (Petchey et al; 2006). To tackle this problem, mathematical models have been successfully combined with experimental setups so that underlying mechanisms can be unraveled (De Laender et al., 2010; Van den Meersche et al., 2004). In addition, the mechanisms provided by these models can be used to develop a predictive framework that allows extrapolation outside the range of tested stress levels and/or environmental conditions (Jager et al., 2010).
Objectives and Methodology
In this PhD project, a combination of BEF experiments and mathematical modelling will contribute to a mechanistic understanding of how direct and indirect effects of stressors on species functional rates and on B interact with trophic interactions in shaping BEF relations. To this end, the following hypotheses will be tested:
H1 The interspecific variability in the sensitivity of species to stressors can be explained by functional trait variability among species in a community.
H2 Stressors affect EF indirectly by changes in B (through non-random species removal/mortality) and potential concomitant knock-on and/or feedback effects (on functional rates and B respectively) mediated by trophic interactions.
H3 Stressors will affect EF directly by impacting species functional rates and concomitant knock-on effects and/or feedback effects (on B and functional rates, respectively), mediated by trophic interactions.
As experimental systems, marine benthic food webs (bacteria-diatoms-copepods) will be used because (1) these communities are highly relevant as they are essential to the overall functioning of marine ecosystems and are very sensitive to anthropogenic stress (Gray et al., 2009) and (2) all partners have advanced experimental and/or modelling expertise in marine benthos research.
Microcosm experiments will be set up in triplicate in thermostatic rooms and will include primary producers (diatoms) and consumers (copepods) as representatives of benthic food webs in NW European tidal flats. The following stressors, which act selectively or non-selectively on the different trophic levels, and are of topical interest in view of their impact on coastal sediments, will be applied: (a) herbicides (e.g. glyphosate) - typically impacting primary producer fitness and diversity (Debenest et al., 2010); (b) suboptimal oxygen levels (hypoxia) - largely impacting primary consumers (harpacticoid copepods) (Levin 2003; Moodley et al. 1997) and (c) metals - affecting all trophic levels (Chapman et al., 2003). Biodiversity of the different trophic levels will be expressed as species richness, evenness and dominance. Diversity measures will be obtained via light microscopic identification and counts (diatoms and copepods) and molecular tools (bacteria). Measured EFs will include carbon and nitrogen cycling rates, bacterial, primary and grazer production.
By gradually increasing complexity, the experimental design will allow to distinguish the relative importance of direct and indirect stressor effects. In a first phase, a single-species approach will yield baseline information on how species respond to stressors. The second level of experimental complexity will focus on the effect of nonrandom species removal in a food web context, i.e. explicitly accounting for (trophic) interactions. Finally, experimental complexity will explicitly include stressor effects on the functional rates of surviving species by dosing the full multi-species assemblages to the selected stressors.
To develop a mechanistic understanding of the obtained experimental results, a food web model will be calibrated to the experimental data. This allows quantifying to what extent non-random species removal changes EF, i.e. the indirect effects mentioned in H2. Likewise, propagation of direct stressor effects (see H3) to changes in EF will be quantified.
Consortium description and feasibility
This PhD research is imbedded in the on-going collaboration between the UGent research groups Marine Biology (MarBiol), Protistology and Aquatic Ecology (PAE) and the Laboratory for Environmental Toxicology and Aquatic Ecology (LETAE). The first two focus on interactions between marine benthic grazers (harpacticoid copepods) and primary producers (diatoms) and maintain culture collections of these organisms. The interfaculty cooperation with the latter (LETAE) provides an excellent opportunity to include anthropogenic stressors. Additionally, the inclusion of a strong modelling component (LETAE, NIOO-CEME) will allow to synthesise the experimental efforts into a predictive framework for future work.
Within this consortium, it is very feasible that this PhD topic yields a PhD thesis after 3 years as data will be collected from short-term experiments and the practical work is highly flexible according to the timeframe and the interests of the student.
References:
Balvanera, P. et al., Ecol. Lett. 9 (10), (2006).- Chapman, P.M. et al., Hum.Ecol. Risk Assess. 9 (4), (2003).- De Laender, F. et al., Environ. Pollut. 158 (5), (2010).- Debenest, T. et al., Vol. 203, pp. 87- 103, (2010).- Duffy, J.E. et al., Ecol. Lett. 10 (6), (2007).- Gray, J. et al., ( Oxford University Press, Oxford, U.K., 2009).- Hillebrand, H. et al., Ecol. Lett. 12 (12), (2009).- Jackson, J.B.C., Philos. Trans. R. Soc. B-Biol. Sci. 365 (1558), (2010).- Jager, T. et al., Phil. Trans. R. Soc. 365, (2010).- Levin, L.A., (2003), Vol. 41, pp. 1-45.- Lotze, H.K. et al., Science 312 (5781), (2006).- Moodley, L. et al., Mar. Ecol.-Prog. Ser. 158, (1997).- Mulder, C.P.H. et al., Proc.Natl. Acad. Sci. U. S. A. 98 (12), (2001).- Petchey, O.L. et al., Ecol. Lett. 9 (6), (2006).- Reusch, T.B.H. et al., Proc. Natl. Acad. Sci. U. S. A. 102 (8), (2005).- Van den Meersche, K. et al., Limnol. Oceanogr. 49 (3), (2004).
Expected outcomes
This PhD project will add environmental realism to the field of BEF research and its results are expected to have far-reaching implications for the management of ecosystems and the services they provide. The project will finally introduce the concepts of biodiversity and ecosystem function into the field of toxicological sciences so that pollutant effects can be assessed at higher levels of biological organization than the typical organismal level effects that are currently used as a basis for the risk assessment of chemicals. Practical benefits include: (1) a doctoral student who is trained in up-to-date multidisciplinary techniques including laboratory and ecological modeling approaches, and (MARES) courses; (2) dissemination of the gathered data to the scientific community in the form of peer reviewed publications (preferably in open access journals), oral presentations at international congresses and a PhD thesis; both ecological and environmental science journals will be targeted.