Figure 1: Early warning signal for a critical transition in a tri-trophic food chain. (a) Time series of $$X_1$$ (blue circles, left axis), $$X_2$$ (green crosses, left axis) and $$X_3$$ (red triangles, left axis) generated by Eq. (2). Only the data subsequently used in the early warning analysis were plotted. Some of the data during the oscillations between $$t = 40$$ and $$45$$ were outside the scale of this graph, with $$X_3$$ exceeding $$30$$. The estimates of top-predator mortality used to calculate the early warning signal are also shown (black dots, right axis).