Population dynamics of Paratylenchus nanus in soil under pasture: 2. Biotic factors and population modelling

Seasonal and monthly sampling of a Paratylenchus nanus population showed th at trends in biomass were similar to those for abundance. A Population Age Index (proportional contribution of each life stage multiplied by stage bio mass) showed population age increased from a minimum in spring to maximum i n winter. From mid-spring to mid-summer, population age was greater in 0-10 than 10-20 cm depth; this tray have been due to a greater proportion of ju veniles developing over this period at the deeper depth. The populations at 10-20 cm deep included a greater proportion of fourth stage juveniles than those at 0-10 em. This may reflect the smaller root resource at 10-20 cm d epth limiting population development. Monthly sampling of patches of high v s low P. nanus density indicated that such patches retain their densities r elative to each other in most months. Evidence is presented for density-dep endence in the P. nanus population at 0-10 cm and density-independence at 1 0-20 cm depth. Multiple regression models were fitted, taking into account all factors (abiotic and biotic) which were significantly associated with P . nanus abundance, and results are discussed to highlight areas still requi ring investigation before a complete model of the population dynamics of th is nematode can be achieved.