We have recently obtained funding to determine the temperature dependence of life. The overall project is exploring temperature responses of enzymes, microbes, soil biogeochemistry, plants, ecosystems and the globe. This PhD will examine how energy fluxes within soil food webs, from microbes to arthropod predators, vary in response to temperature within this broader project. The successful candidate will take advantage of natural belowground temperature gradients adjacent to geothermal hotspots where soil temperature can decline from ~40C to 18C within 20 m. We wish to determine how soil food-web structure and energetics change along geothermal temperature gradients and whether differential thermal responses of soil organisms across trophic levels contribute to changes at the food-web scale (see detailed description below). The position will be based at the University of Waikato, where you will be supervised by Andrew Barnes, Charlotte Alster and Louis Schipper.

Applicants will be independent and highly motivated with:

  • An Honours or MSc degree in a relevant subject (e.g., soil ecology, ecological entomology, environmental (bio)geochemistry,)
  • Experience with lab and/or field experiments
  • Sound skills in analysing data (preferably in R)
  • Excellent communication skills in English (spoken and written)

Annual stipend for 3 years: $27,500 NZD (plus an additional $6,500 to cover annual fees)

Closing date: we will begin reviewing applications after the 12th of March 2021 until the position is filled. The position will start after July 2021.

To apply: please send as a single document: 1) a letter of motivation and 2) your CV (including contact information for 2 referees) to Andrew Barnes (andrew.barnes@waikato.ac.nz). Your letter of motivation should describe why you are specifically interested in this PhD project.

Please note: we welcome applications from all countries. However, at the time of recruitment, we must be mindful of the border restrictions put in place by the New Zealand government due to the COVID-19 pandemic. While there are currently possibilities for recruiting PhD students internationally, this is a rapidly changing situation that may affect our ability to recruit from overseas.

Detailed project description:

Climate warming is expected to have wide-ranging effects on biological systems, from enzymes1, to whole organisms2, to food webs3,4 and ecosystem processes5,6. Determining linkages among responses to temperature across these levels of biological organisation is a key challenge in understanding ecosystem impacts of warming.

This project will utilise a series of temperature gradients at geothermally warmed sites in the north island of New Zealand to investigate how temperature alters soil food web structure and energetics. The student will sample entire soil food webs along the temperature gradients and use standard methods for quantifying microbial biomass and respiration, as well as describing community structure of soil micro- and mesofauna.

These naturally warmed field sites can be used to test a number of major hypotheses on how soil food webs will respond to warming. For example, the student will be able test the general expectation that average body size should decline with increasing temperature7 by analysing mass-abundance relationships within trophic groups of soil fauna. Furthermore, by constructing food webs and quantifying energy fluxes along trophic interactions6,8, the student can test if geothermally warmed soils harbour simplified food webs4 caused by increasing energetic imbalance at higher trophic levels and if this causes shifts in ecosystem processes.

Further experimental manipulations will be carried out to investigate underlying mechanisms that give rise to food web responses along the natural temperature gradients. For example, lab trials can be run to measure the temperature dependence of metabolism for different taxa in order to test whether the thermal optima of soil organisms varies across trophic levels in soil food webs. Additionally, intact soil food webs can be extracted from soils across the geothermal temperature gradients. They can then be experimentally warmed to determine how adaptation of soil food webs to different temperatures may influence structural and functional responses to future warming scenarios.

Relevant literature:

1.          Prentice, E. J., Hicks, J., Ballerstedt, H., et al. The inflection point hypothesis: The relationship between the temperature dependence of enzyme-catalyzed reaction rates and microbial growth rates. Biochemistry 59, 3562–3569 (2020).

2.          Dell, A. I., Pawar, S. & Savage, V. M. Systematic variation in the temperature dependence of physiological and ecological traits. Proc. Natl. Acad. Sci. U. S. A. 108, 10591–10596 (2011).

3.          Fussmann, K. E., Schwarzmüller, F., Brose, U., Jousset, A. & Rall, B. C. Ecological stability in response to warming. Nat. Clim. Chang. 4, 206–210 (2014).

4.          O’Gorman, E. J., Petchey, O. L., Faulkner, K. J., et al. A simple model predicts how warming simplifies wild food webs. Nat. Clim. Chang. 9, 611–616 (2019).

5.          Alster, C. J. Microbes adjust to heat. Nat. Ecol. Evol. 3, 155–156 (2019).

6.          Schwarz, B., Barnes, A. D., Thakur, M. P., et al. Warming alters energetic structure and function but not resilience of soil food webs. Nat. Clim. Chang. 7, 895–900 (2017).

7.          O’Gorman, E. J., Zhao, L., Pichler, D. E., et al. Unexpected changes in community size structure in a natural warming experiment. Nat. Clim. Chang. 7, 659–663 (2017).

8.          Barnes, A. D., Jochum, M., Lefcheck, J. S., et al. Energy flux: The link between multitrophic biodiversity and ecosystem functioning. Trends Ecol. Evol. 33, 186–197 (2018).