Figure 2.

When there is directional environmental change the probability of extinction increases with increasing selectivity and harvesting intensity. K indicates the carrying capacity of the environment, which will determine the population size when environmental change begins, and fecundity is the average fecundity of a female who is well adapted to the environment. The columns headed ‘both’ show probabilities of extinction when both male and female adults are harvested at random. The columns headed ‘male only’ show extinction probabilities when only adult males are harvested. The y-axes show harvesting intensity, expressed as the proportion of the male population removed per time step (for the ‘both’ columns the harvesting intensity was reduced by 50% for each sex so that the same overall number of animals were removed). The x-axes show the degree of selectivity expressed as the coefficient S from the model, with 0 indicating that harvesting is random and the degree of selectivity increasing as the value increases such that a value of 4 indicates a strong preference for the most ornamented males—see electronic supplementary material, figure S2. All probabilities calculated from 80 runs of the model over 600 time steps and with the increase in the environmental variable set to 0.005 per time step. See the electronic supplementary material for full details of the model.