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Fire Ant Population Model

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Model Verification and Validation


The value of a simulation model is in part dependent on its ability to realistically mimic targeted response variables. Initially parameterized models frequently fail to accurately fit observed data. To correct this situation, some parameters or functions are adjusted within biologically reasonable limits, and the new model output is again compared with observed data. This process is called model verification. In contrast, validation is the comparison of output from a verified model with independent data, followed by statistical analyses that test the degree of fit. Without a statistically rigorous validation, a verified model represents little more than a sophisticated curve-fitting and does not enable a statement of certainty as to its ability to capture response to major climatic, biotic, edaphic, and management variables.

Worker ants tending larvae and queen

The ability of the proposed fire ant simulation model to capture within-colony and between-colony dynamics in a heterogeneous environment will be tested using a rigorous statistically-based parameterization-verification-validation procedure. A detailed description of the statistical basis for the proposed parameterization-verification-validation approach is provided by Wu & Wilson (1998).

We hope to partially verify and validate the simulation model using long term data sets such as the one presented by Greenberg et al. (1992). If necessary, experiments would be conducted to study colony dynamics in the Bryan and College Station area. In each study site, the number of fire ant colonies would be marked at the beginning of the study period and their queen status (single or multiple) noted, possibly using the methodology developed by Bhatkar et al. (1992). Periodic sampling would determine the number of workers of each caste during colony growth.

Red imported fire ant mound, cut-away

Because mating flights follow periods of precipitation, more frequent sampling after rains would be necessary to determine the number of reproductive queens and males and the establishment of new colonies. The results from these experiments would provide additional validation data for the model, again with the primary parameters obtained from the literature.

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Document Author:

L. T. Wilson
Send mail to L. T. Wilson

Photos:

Courtesy of    Bart M. DREES  and AESRG

Revised:

November 18, 2002
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