The "Native Fish" Bayesian networks

We present the “Native Fish” Bayesian network, a pedagogical model developed to introduce Bayesian networks to ecologists. The network models a hypothetical situation where pesticides are used on crops which impact upon the native fish population in a nearby river system. The network is developed incrementally. The first basic network, Version 1, contains nodes for Annual Rainfall, Drought Conditions, Tree Condition, Pesticide Use, Pesticide in River, River Flow and Native Fish Abundance. The network is augmented in Version 2 with nodes for ENSO, Crop Yield and Irrigation. In Versions 1 and 2 the nodes are all discrete and qualitative. In Version 3, the nodes are made continuous then discretised, and the CPTs are generated from equations. In Version 4, we present a decision network, where Pesticide Use and Irrigation become decision nodes, utility nodes are added to represent Landholder Income, Pesticide and Irrigation Costs, as well as the Environmental Value associated with native fish abundance. For each version, we show screenshots of the Netica BN software showing the posterior probabilities computed for a range of predictive and diagnostic reasoning scenarios.