Population Dynamics and Interactions Between Eight Genera of Nematodes: An Empirical Analysis.

Knowledge of population dynamics of soil-borne organisms is critical to developing flexible, information-based farming systems that manage these organisms for maximum expected profit. This article presents a statistical population dynamics model for eight genera of nematodes using nematodes counts taken from plots in the “Cullars Rotation” which is the oldest soil fertility experiment in the Southern United States. The dynamic models are estimated with monthly observations allowing a closer examination of the interactions of the various genera and the seasonality of population growth and decline. The model includes a spatial autocorrelation component in order to account for location effects between experimental samples. The model, which is specified to have a multiplicative random error because of its desirable properties, is expressed in linear in parameters (log-log) as follows:

Where pit is population level of the ith organism at time t; wi is the distance/connectivity (spatial) matrix; pj,t-1 is population level of the genera interacting with the ith organism at time t-1 (including its own); Xik is a set of k explanatory variables for the ith organism (binary variables to represent nitrogen application, monthly intercepts, and crop rotation sequence); bij and gik are the parameters to be estimated; and uit is a random error term.

The results showed that the lagged own-population effect was statistically significant for all genera and that many of the lagged population levels of other genera were also statistically significant. Thus, it can be concluded that population dynamics are highly important for all eight genera. Populations tend to decrease during January but they go up quickly again during March and remain steady until September when there is a significant increase in the population of root-knot, dorylaimus, microbivorous, and lesion. Nitrogen affected positively populations while the best rotation for controlling plant feeder nematodes was clover.