A Comparison of the Spatial Distributions of Three Plant-Parasitic Nematode Species At Three Different Scales

The spatial distributions of three nematode species (Longidorus elongatus, Longidorus goodeyi and Rotylenchus goodeyi) were intensively sampled in a permanent pasture field. Three regular sampling grids were employed covering scales ranging from 5 cm to 50 m. Geostatistical analyses were used to quantify any spatial dependencies found within and between 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 levelling off of variance at larger scales. The only inter-species correlations detected were at scales up to about 20 cm between L. elongatus and L. goodeyi, species which share a similar environmental niche. A power model provided the best description of the semivariograms and is discussed in relation to "fractional Brownian motion", a scaling property present in many natural systems.