Figure A2.2 The kelp-urchin dynamical model is run 500 times with the default parameter set and stochastic urchin recruitment. Initial conditions are those of an urchin barren. Plot ‘a’ compares model output with observed data from urchin barrens in Norway north of 68°N (Ling et al., 2015). Each bar shows how frequently an observation or simulation ends in a state with a given urchin abundance range (0–10, 10–20, …, 150–160). Plot ‘b’ compares model age distribution with observed data from Hammerfest urchin barrens (Fagerli et al., 2015). Only urchins of ages 2+ are considered owing to potential biases in the observations. The graphic shows urchin abundance per one-year age class as a percentage of the total number of urchins of age 2+. Plot ‘c’ compares model biomass against size-class distribution with observed data from Hammerfest urchin barrens (Fagerli et al., 2015). Only urchins over 20 mm in size are considered owing to potential biases in the observations. The plot shows the amount of urchin biomass per size class as a percentage of the total urchin biomass.