Fig. 2. Performance of center-of-gravity (A) and best-receptor (B) models with different weightings of rheotaxis and tropotaxis. For each weighting, 1000 searchers were simulated for up to 1500 time steps (30 s), as described in Materials and methods. The vertical lines span the range of time steps taken to reach the source, while the horizontal lines indicate the median time taken. The closed circles indicate the number of searchers that reached the source. Few searchers reached the source with a weighting of less than 0.5, whereas weightings greater than 0.8, resulted in some searchers reaching the source while others never did. All searchers reached the source in close to the minimum time with intermediate weightings. For comparison, the average crab found the source in approximately 1500 time steps (30 s).