EN
The model of ideal free distribution (IFD, Fretwell and Lucas 1970, Fretwell 1972) can predict the optimal distribution of individuals of a given animal population between patches of different resource profitability. The two most important assumptions of the IFD model are that (1) each individual is able to assess the level of resources and chose the most proficient location which offers the highest possible fitness gain, and (2) each individual is free to move from one patch to another with no costs involved in its relocation. The IFD model predicts that the density of an animal population reflects resource profitability: the higher the resource levels (resource productivity), the higher the population density (Figs. 1 and 2a). While early examples demonstrated the great predictive value of the IFD model, more recent studies have shown that the model is too robust to accurately reflect animal distribution. Considerable empirical data have shown that there are consistent deviations from the IFD, and that densities in proficient sites are often lower than expected from the outcome of this model, and vice versa. The original imperfect IFD model (Fig. 2a) has therefore been gradually replaced by various modifications, including those that consider the inability to correctly assess the resource profitability level (Fig. 2b), the effect of competitive interference (Fig. 3), differences in superiority in resource competition (Fig. 4), and other factors such as travel costs. However, the aforementioned modifications are not as important for individual fitness as the separate components of individual growth P, either by reduced assimilation A or elevated respiration R (P = A - R).