Simulation studies of Senegalese Grasshopper ecosystem interactions I: the ecosystem model

I present a model that could simulate the ecosystem dynamics of the Senegalese Grasshopper (Oedaleus senegalensis, Krauss) in the Sahel. It included the migration of the grasshopper by simulating the population dynamics and migration in a number of locations along a south-north transect. The model ecosystem in each location comprised: (i) millet, (ii) a natural Sahelian grass representing the grassland vegetation, (iii) the Senegalese grasshopper; (iv) a less important grasshopper, Acrotylus blondlii, Saussure; (v) two species of grasshopper egg pod predators; and (vi) 24 species of birds that prey on grasshoppers. The model was rain-driven, used real climatic measurements as input, and was able to include the impact of grasshopper control measures such as treatment with chemical pesticides and the biopesticide Green Muscle. The model has a wide variety of possible applications and may be used both for fundamental and applied purposes. Theoretic application may consist of investigating of the relative roles of natural egg pod predators and the many grasshopper-consuming bird species, as well as the ecological balance of a pest species that is under extensive natural control. Practical application may involve simulation of the impact of various control strategies, both on millet yield and the environment. Several simulations are presented to demonstrate the performance of the model, and to demonstrate the importance of the food web interactions, the temperature-dependent action of the biopesticide Green Muscle, and the importance of including the grasshopper migration in the model. One key result is that predation by the birds in the model might be replaced by a constant mortality rate without considerably changing the simulation of the population dynamics of O. senegalensi.