Fit, efficiency, and biology: Some thoughts on judging food web models

Modelling Size Structured Food Webs Using a Modified Niche Model with Two Predator Traits

“…the body mass based niche model) to provide very good fit to empirical food webs when the fit is judged by comparing values of summary statistics of food web structure [17], [29]. There are other means of comparing food web models to empirical data, such as comparing the proportion of correctly predicted links or calculating model likelihood [16], [19], [38], [46]. However, fitting models to real data on food webs remains a tricky task [38] which may suffer from limitations beyond the choice of the appropriate metrics.…”

“…There are other means of comparing food web models to empirical data, such as comparing the proportion of correctly predicted links or calculating model likelihood [16], [19], [38], [46]. However, fitting models to real data on food webs remains a tricky task [38] which may suffer from limitations beyond the choice of the appropriate metrics. Sampling effects may bias empirical descriptions of food web structure [47], [48], which is certainly true also in the case of size structure because many common sampling methods are size selective and provide a distorted view of community composition in aquatic (e.g.…”

“…[53]–[55]) habitats. Moreover, I argue that stochastic structural food web models are better suited for studies simulating food web dynamics than for fitting to real data because they only describe food web structure without providing mechanistic explanations [38]. For the purpose of simulation studies, it is important that manipulating the size structure of food webs using the two traits allometric model has only minor consequences for other structural properties of food webs.…”

“…Stochastic food web models have been fitted to empirical data in this fashion [19], [20], [23], [46], but the value of such comparisons is limited because the models are purely phenomenological and do not provide mechanistic insights [38]. It has been shown that any model obeying a few simple constraints will fit real food web data similarly well [56].…”

“…The metrics used were: the proportion of basal, intermediate and top species, the proportion of herbivores, mean and maximum trophic level, mean omnivory level, clustering coefficient, standard deviation of generalism and vulnerability, maximum diet similarity and mean path length (the definitions follow [16]). I refrained from comparing these metrics directly to real data because improving the, already good, fit of the niche model was not an objective of this paper and because the utility of such comparisons for evaluating food web models is limited [38]. I instead focused on comparing the different models among themselves to test whether the changes in size structure in these models lead to changes in other structural properties.…”