The Use of Cellular Automata Modeling Approaches to Understand Potential Impacts of Genetically Modified Plants on Plant Communities

Ricardo Colasanti
National Research Council, USEPA NHEERL WED, University of Glamorgan

Rod Hunt
University of Exeter

Lidia S. Watrud
USEPA NHEERL WED

The development of models is of interest to ecologists, regulators, and developers, since it may assist theoretical understanding and decision-making in experimental design, product development, and risk assessment. A successful modeling methodology for investigating such characteristics must include both a plant’s spatial and functional behavior within a plant community as a function of its physiology. However, can the full dynamics of a plant community emerge from the physiological properties of its constituent species?

Over the last twenty years successful simulations of spatial processes of vegetation have been conducted by a number of authors (Barkham & Hance 1982; Crawley & May 1987; Green 1989; Inghe 1989; Colasanti & Grime 1993) using a cellular automata (CA) method of modeling where a plant’s distribution within a two-dimensional environmental grid is determined by rules relating to phenomena such as seed dispersal, clonal expansion, and interactions with adjacent plants. We believe that these same methodologies can be utilized in order to predict the potential impacts of genetically modified (GM) plants. To do so we must understand how the engineered traits are expressed in an ecological context.

It would be a daunting task to experimentally evaluate the full multiplicity of potential pair-wise interactions between GM plants and native plants under a broad variety of actual environmental conditions. We propose, therefore, to model interactions between GM plants and the natural environment by describing the plants and the effect of the GM trait in terms of plant functional types (Grime 1979). This approach takes the external factors which limit the amount of plant material present in any habitat and classifies them into two categories: (1) stress, defined with regard to the availability of nutrients, and (2) disturbance, which refers to the destruction of plant material. The ecological characteristics of plants both natural and genetically modified can be described based on functional type, i.e. as determined by their quantifiable physiological relationships to stress and disturbance. By ascribing the large number of plant ecological characteristics to a smaller number of functional types the problem becomes tractable.

The presentation will describe a CA individual-based model constructed from a plant functional type rule base, that does indeed reproduce all of the main population attributes and vegetation processes that are observed in field conditions. Competition (both natural and genetically modified) in relation to environmental factors (both natural and man-made) has been successfully simulated in considerable detail. We will also describe how the model will be validated using data from field and mesocosm studies being carried out by researchers from WED.

References: Barkham JP, Hance CE. 1982. Population dynamics of the wild daffodil (Narcissus pseudonarcissus) III Implications of a computer model of 1000 years of population change. Journal of Ecology 70: 323-344. Colasanti RL, Grime JP. 1993. Resource dynamics and vegetation processes: a deterministic model using two-dimensional cellular automata. Functional Ecology 7: 169-176. Crawley MJ, May RM. 1987. Population dynamics and plant community structure: competition between annuals and perennials. Journal of Theoretical Biology 125: 475-489. Green DG. 1989. Simulated effects of fire, dispersal and spatial pattern on competition within forest mosaics. Vegetatio 82: 139-153. Inghe O. 1989. Genet and ramet survivorship under different mortality regimes - a cellular automata model. Journal of Theoretical Biology 138: 257-270.

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