Dynamics of sympatric Paratylenchus nanus and Paratrichodorus minor populations in soil under pasture

Populations of both Paratrichodorus minor and Paratylenchus nanus in a graz ed pasture in Waikato, New Zealand were assessed in single 2.5 em diam. cor e samples over six successive seasons. Neither seasonal periodicity nor a c onsistent vertical distribution pattern was observed in the P. minor popula tion. P. nanus had distinct spring and summer population maxima and was mor e abundant at 0-10 than 10-20 cm depth. P. minor but not P. nanus abundance was significantly correlated with rainfall and an activity index combining rainfall and soil temperature for the week before sampling. Significant co rrelations among P minor, P. nanus and concentrations of some soil nutrient s seemed to reflect soil nutrient interactions with other biotic factors su ch as plant growth. There was no evidence for competition between these two nematodes. Host root resource, spatial aggregation and differences in morp hology that indicate niche differences are discussed as possible reasons fo r the observed lack of competition.