A COMPARISON OF THE SPATIAL DISTRIBUTIONS OF 3 PLANT-PARASITIC NEMATODE SPECIES AT 3 DIFFERENT SCALES

The spatial distributions of three nematode species (Longidorus elonga tus, Longidorus goodeyi and Rotylenchus goodeyi) were intensively samp led in a permanent pasture field. Three regular sampling grids were em ployed covering scales ranging from 5 cm to 50 m. Geostatistical analy ses were used to quantify any spatial dependencies found within and be tween nematode species. All three species were present in most samples and in general the raw counts were positively skewed. Semivariograms of transformed counts (log(10)(counts + 1)), showed similar, generally isotropic, trends for all three species with the variance increasing with separation distance. There was no evidence of a sill i.e. a level ling off of variance at larger scales. The only inter-species correlat ions detected were at scales up to about 20 cm between L. elongatus an d L. goodeyi, species which share a similar environmental niche. A pow er model provided the best description of the semivariograms and is di scussed in relation to ''fractional Brownian motion'', a scaling prope rty present in many natural systems.