NEMATODE MOVEMENT ALONG A CHEMICAL GRADIENT IN A STRUCTURALLY HETEROGENEOUS ENVIRONMENT .2. THEORY

The effects of structural heterogeneity on both chemical diffusion and nematode movement are examined with the development of a theoretical model. The model considers three factors affecting nematode movement: soil structure, nematode foraging strategy and chemotaxis. Using a con tinuous model, we develop a discrete system which allows nematode trai ls to be simulated in any of the four experimental conditions given by Anderson et al. (1997). We show that structural heterogeneity causes mixed levels of attractant concentration over small areas as well as ' 'fingering'' of the attractant. Soil structural heterogeneity also res tricts the foraging strategy of the nematode which then becomes a stra tegy to avoid structural ''traps''. The effect of localised increases in structural density is shown to increase significantly '' fingering '' of the attractant.