Mesozoic Ecosystem Dynamics: Modelling dinosaurs in their natural environment

Despite high levels of complexity and a vast array of different ecosystems, the modern terrestrial biosphere has a number of unifying properties. One such property and a key feature of most ecosystems is the terrestrial ecological pyramid. Most biomass is contained within the primary producers, typically photosynthetic plants, with herbivores an order of magnitude less massive and carnivores composing a relatively minor portion of the biomass. This biomass structure holds over almost all terrestrial ecosystems, independent of productivity, climate, biome etc. Even during significant ecosystem restructuring, for example Pleistocene megafauna loss (Malhi et al., 2016), the overall biomass structure remains intact. Recent computer modelling has shown this to be an emergent feature of the biosphere, emerging from the basic ecological operations of different functional groups and their interactions (Harfoot et al., 2014).

 

However, it appears that the biosphere was very different during the interval when large dinosaurs roamed the Earth, the Mesozoic Era (Figure 1). Estimates suggest that much more biomass was contained within the large herbivores (Table 1), for example the diplodocus and other sauropod dinosaurs, perhaps more than 10 times greater than the most massive modern large herbivore populations. These observations seem to break most of the lessons learnt from studying modern ecosystems and add further complications to existing problems of how these creatures were able to evolve, grow and maintain such massive bodies.

 

Location (scenario) Estimated large herbivore population density (animals/km2) Total large herbivore biomass (kg/km2)
Murchison Falls Park 44.64 28,038
Morrison formation (mammalian metabolism) 11.52 – 15.41 37,643 – 42,309
Morrison formation (lizard metabolism) 102.81 – 129.81 317,236 – 376,923

The Madingley Model (Harfoot et al., 2014) is the first of a new class of computational ecological model, a General Ecosystem Model (GEM). It takes the basic ecological functions and interactions (metabolism, predation, eating, reproduction, mortality and dispersal) of different functional groups of organisms (e.g. autotrophs, herbivores and carnivores) and simulates them across the whole globe. From just these localised operations many large scale features emerge, such as life history, ecological pyramids and global ecosystem gradients. The Madingley Model has been shown to do an excellent job at simulating the large scale structure of the modern natural biosphere and yet given appropriate forcing is able to simulate entirely different ecosystem structures (Figure 2). The difference in ecosystem structure illustrated in Figure 2B versus 2A is brought about by an increase in herbivory assimilation efficiency, which could be driven by increased efficiency in digestion by herbivores or an increase in the nutritional value of the available food, possibly due to elevated CO2 atmospheric concentrations (Gill et al., 2018), or a combination of both. The experimental strand of this research will investigate the nutritional value of Mesozoic analogue plant taxa, grown under a range of CO2 concentrations simulating estimates for Mesozoic atmospheric concentrations.

Using the Madingley Model to simulate Mesozoic ecosystems will help us to understand the functioning of the terrestrial biosphere at a time when massive dinosaurs roamed the Earth and how such creatures could grow to such large sizes and overall community biomasses. There is the opportunity to use other ecosystem modelling techniques, such as biogeographical or trophic network modelling (Dunhill et al., 2016) in specific examples with exceptional data, such as the Morrison Formation (Farlow et al., 2010). This would provide greater detail of ecosystem interactions, further investigation of the potential functioning of Mesozoic ecosystems and an interesting comparison of different ecosystem modelling techniques. The Mesozoic will provide an out of sample test of how well GEMs can simulate very different ecosystem structures, which will be important as the models are used to simulate anthropogenic impacts on natural ecosystems. New insight will be gained into the effect that ecosystem structure has on the stability of the biosphere or its resilience to large perturbations, such as the asteroid that killed the mass extinction of the dinosaurs, and whether the way we are affecting natural ecosystems could affect its long term stability.

 

Objectives

This project will develop GEM (General Ecosystem Model) simulations for the Mesozoic and use these to investigate the functioning and structuring of the global biosphere. The specific objectives will be to:

  • Produce a suite of GEM simulations driven by existing climate and tectonic models of the Mesozoic and test these against fossil data and other ecosystem modelling techniques.
  • Investigate the evolutionary drivers of Mesozoic ecosystem structures, including an experimental investigation of plant nutritional value under Mesozoic atmospheric conditions.
  • Test the resilience of the various ecosystem structures to perturbations, both on a local and global scale, and relate these to Mesozoic ecosystem events.

 

Potential for high impact outcomes

It is expected that this project will produce a number of high impact journal articles, focused on the three main objectives of the proposal. There is significant potential to further our understanding of the fundamental functioning of the terrestrial biosphere and the successful candidate will also have the opportunity to extensively use the Madingley Model GEM and be involved in its development and future direction.

 

Training

The student will be trained in the use and development of the Madingley Model GEM, as well as the analysis of climate model data. The student will also be trained in geochemical analytical techniques, e.g. Fourier transfer infrared spectroscopy and pyrolysis-gas chromatography-mass spectrometry. Being based in the Palaeo@Leeds and Cohen Geochemistry research group gives the student access to a wealth of palaeoclimate and palaeontological expertise, not only from the supervision team, but the wider research cluster. As part of the Panorama NERC DTP, there will be many opportunities to develop new skills. The student will be expected to attend and present at national and international scientific meetings.

 

Student profile

No applicant will have all the required skills and knowledge prior to starting this PhD and the strong interdisciplinary nature of the research means that it is suitable for a broad range of scientific backgrounds. These include, but are not limited to biology, palaeontology, geology, environmental science, physics, maths, computer science etc.

 

International partners

The student will join the international community developing the Madingley Model GEM. This includes a large number of individuals and institutions, including the UN Environment World Conservation Monitoring Centre (UNE WCMC), University of Copenhagen, Stockholm Resilience Centre, Northern Arizona University and the Zoological Society of London.

 

References

Dunhill, A.M., Bestwick, J., Narey, H. and Sciberra, J., 2016. Dinosaur biogeographical structure and Mesozoic continental fragmentation: a network-based approach. Journal of Biogeography, 43(9), 1691-1704.

Farlow, J.O., Corolan, I.D. and Foster, J.R., 2010. Giants on the landscape: modelling the abundance of megaherbivorous dinosaurs of the Morrison Formation (Late Jurassic, western USA). Historical Biology: An International Journal of Paleobiology, 22(4), 403-429.

Gill, F.L., Hummel, J., Sharifi, A.R., Lee, A.P. and Lomax, B.H., 2018. Diets of giants: the nutritional value of sauropod diet during the Mesozoic. Palaeontology, 61(5), 647-658.

Harfoot, M.B.J., Newbold, T., Tittensor, D.P., Emmott, S., Hutton, J., Lyutsarev, V., Smith, M.J., Scharlemann, J.P.W. and Purves, D.W., 2014. Emergent global patterns of ecosystem structure and function from a mechanistic General Ecosystem Model. PLOS Biology, 12(4), e1001841.

Malhi, Y., Doughty, C.R., Galetti, M., Smith, F.A., Svenning, J-C. and Terborgh, J.W., 2016. Megafauna and ecosystem function from the Pleistocene to the Anthropocene. Proceedings of the National Academy of Sciences of the United States of America, 113(4), 838-846.

Scotese, C.R., 2001. Atlas of Earth History, PALEOMAP Project, Arlington, Texas, 52pp.