Movie S5.

A simple spatially implicit model, featuring a single class of worm and five free parameters, is described in SI Appendix, 2.1 Spatially Implicit Model. The worm count predicted by this model is taken at t= 144 h, the same time at which the worm count was experimentally measured. This timing corresponds to the bacterial population being driven to collapse by the C. elegans population on the smallest plate (R= 2 cm). This movie shows the sensitivity of the model’s predicted worm count to varying its five free parameters. The parameter a, the maximum rate at which worms can consume bacteria, is varied over a 20-fold increase, from a= 1 to a= 20 cells/min. The parameter ϵ, the worm reproductive rate, is varied from ϵ= 3.5×10−3 to ϵ= 5.5×10−3 min−1. The parameter c, the saturation rate of the Hollings type II functional response (SI Appendix, Eq. S.3), is varied over a fivefold increase, from c= 5×10−10 to c= 2.5×10−9 cells−1. The parameter σ, which controls how the worms’ foraging efficiency changes with plates size (SI Appendix, Eq. S.4), is varied over a fourfold increase, from σ=500 to σ= 2,000 cm2. The parameter s, the rate at which bacteria is spread by farmers (SI Appendix, Eq. S.5), is varied over a 15-fold increase, from s= 1×10−11 to s= 1.5×10−10 min−1cm−2.