The influence of neighbours on individual performance in natural populations of the lichenized ascomycete Umbilicaria spodochroa was investigated using three different neighbourhood models; the polygon model, the fixed radius model and the nearest neighbour model. The data set consisted of the exact position of the holdfast points of the peltate lichens within 29 sample squares in crowded populations as well as the mass, diameter, and no. of apothecia of all thalli. A total of 11246 individual thalli were sampled and measured. The predictive power of all three neighbourhood models was moderate, but highly significant for the whole data as well as within most individual sample quadrats. The nearest neighbour model had the best predictive success, closely followed by the polygon model. The fixed radius model had approximately half the power of the two other models. We suggest that the difference is due to different degrees of realism in the models. Thallus mass was commonly the performance parameter best predicted, followed by thallus diameter and number of apothecia. The predictive power of the models for these natural populations was comparable to values obtained in several laboratory studies with vascular plants. The predictive success of the three different models was strongly correlated for single populations, indicating different levels of interference in different populations.