Twin origin of DEB and PSPD research
DEB research, as done at the Dept. of Theoretical Biology of VU University Amsterdam during 1985-2015, started in the spring of 1979, when Bas Kooijman, then working at the Laboratory of Applied Technological Research TNO-Delft, was asked to solve to problem of quantifying how toxicants affect reproduction of waterfleas, and how this affects population and ecosystem dynamics. The ecological literature was of little help at that time for translating effects on individuals into that on populations; existing models for the uptake and use of substrates by organisms were scarce and primitive or problematic.Bas seeked advice from his former room-mate Hans Metz at the Institute of Theoretical Biology Leiden, who was closely collaborating with Odo Diekmann, then working at the Centre for Mathematics and Computer Science CWI-Amsterdam. Hans was interested in the problem because it is basic to population dynamics, and Odo saw possibilities of application and further development of semi-group theory, on which he was working. This collaboration was the start of two twin research lines, which later involved an increasing number of workers: the DEB theory for structuring individuals and the theory of Physiologically Structured Population Dynamics (PSPD) for the translation of properties of individuals into that of populations.
A first paper on the translation of effects on individuals to that on populations was written in 1982 (Kooijman, S.A.L.M. and Metz, J.A.J. 1983 On the dynamics of chemically stressed populations; The deduction of population consequences from effects on individuals. Ecotoxicol. Environ. Saf., 8: 254-274) for immediate needs, but both authors felt that science was in need of a much more fundamental approach.
PSPD theory
Three events accelerated the early development of PSPD theory.- A very simulating colloquium on PSPD was organized at CWI-Amsterdam by Odo, from which a book appeared three years later (Metz, J. A. J. and Diekmann, O. (eds) 1986 The Dynamics of Physiologically Structured Populations. Springer Lecture Notes in Biomathematics 68, Springer-Verlag, Berlin).
- Andree de Roos was appointed in 1984 on an acquired grant from NWO (Dutch National Science Foundation), which resulted in PhD-thesis Roos, A. de 1989 Daphnids on a train: Development and application of a new numerical method for physiologically structured population models, under supervision of Hans Metz. Andree is still working on PSPD theory at Amsterdam University.
- Horst Thieme was appointed at the CWI-Amsterdam in 1985, who wrote a fundamental paper. (Thieme, H. R. 1988, Well-posedness of physiologically structured population models for Daphnia magna. J. Meth. Biol. 26: 299-317.) Horst, went to Arizona University in Tempe, continuing working on PSPD theory. Mats Gyllenberg was also involved in research on structured population dynamics at CWI, and later specialized on theory for structured metapopulations. He went to the University of Turku to continue work on PSPD.
DEB theory
Because waterfleas were popular in ecotoxicological research, DEB theory was initially developed and tested on these creatures. An intensively interacting group of workers started modelling Daphnia energetics.Physicist Roger Nisbet, then at Strathclyde University Scotland, worked on delay differential equations for analysing stage-structured (insect) population dynamics with Bill Gurney. He tried to generalize his results to more general physiologically structured individuals. He met experimental biologist Ed McCauley (Calgary University, Canada, where he still works) in 1983, and, as a result, became involved in modelling DEB for waterfleas. Hans Metz spent a short sabbatical leave in Strathclyde, and brought Roger into contact with Bas. A stimulating workshop on modelling waterflea eco-physiology was organized in 1985 at TNO-Delft. The Scots-Canadian waterflea-work culminated in the paper Nisbet, R. M., Murdoch, W. W. and McCauley, E. and Gurney, W. S. C. 1988 The physiological ecology of Daphnia II: A new model of growth and reproduction, Ecology. Continued research revealed, however, that the model was too complex for useful PSPD analysis.
Tom Hallam identified modelling effects of pollutants in the environment as the main field of interest for his group at Tennessee University in Knoxville, and visited Bas in Delft in 1983. This initiated a long-lasting collaboration. Tom invested a lot of effort in developing parallel computational methods for integrating partial differential equations for PSPD.
When Bas moved to Amsterdam in 1985, his ecotoxicological motivation changed into a more fundamental and general biological one, and waterfleas where no longer the primary focus of interest. DEB's implications for body size scaling relationships were already known in 1983 (and published in 1986), which convinced Bas that the DEB theory had a much wider applicability. Research on the application to micro-organisms was initiated in 1985. A full integration of the animal and microbial model formulations occurred in 1992, with the notion of changing shapes. Contacts with Ad Stouthamer and his microbiological group at the Vrije Universiteit in Amsterdam fired the interest for simultaneous energy and mass budgets. The aging module was created in 1992; the full multivariate approach, which is required to model simultaneous nutrient limitation in algal and plant eco-physiology, was developed after the invention of Synthesizing Units in nov 1995 (and published in 1996). This multivariate formulation eventually allowed to replace the last empirical assumption of the DEB theory (the one on reserve kinetics) by a more fundamental one. The progam since 2002 strongly developed into the directions of ecosystem (direct and indirect syntrophy) as well as in sub-organismal organisation.