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Issues of scale in individual-based models : applications in fungal and plant community dynamics

The central question addressed in this thesis is whether descriptions o f the dynamics o f ecological systems at one scale may be effectively used as descriptions of the dynamics o f ecological systems at larger scales. This question is addressed in the context o f the dynamics o f fungal communities. A simple experimental system and complementary theoretical approach, in the form o f an individual-based (cellular automaton) model, is presented. Experimental results derived from small-scale systems are used to quantify parameters of the model; results from large-scale experimental systems serve to test the model. The theoretical analyses clearly demonstrate that the dynamics observed are a result of both local and non-local features o f the experimental system. In cases such as this the immediate extrapolation of results derived from experiments conducted out of the context o f the community to represent system scale behaviour is not possible. In response to this observation a generic framework is developed to allow the consideration of effects at a range of scales through contextual parameterisation of localised dynamics. The framework is directed toward plant systems where a large body of experimental data exists, and may be parameterised by that experimental data. It represents the essential features o f individual interactions in terms of competition for space and resource, and the behaviour of a given plant is described in terms of functional traits. Model runs demonstrate complex community patterns suggestive o f a known biological phenomena, succession, that arises as a consequence of the coupling between the community and environment. This coupling may allow the long-term coexistence o f species through some particular balance in individual function (traits) across the community. A search mechanism is determined to allow combinations o f trait values at the scale o f the individual to be assessed for a particular community-scale phenomenon. Initial results demonstrate that this mechanism may identify and converge on combinations of trait values that give rise to, in this case, a simple measure o f diversity. The manner in which the generic framework developed may be applied to further the investigation into fungal community dynamics is addressed.