Big predators are known to be important in maintaining ecosystems function and biodiversity. Inferring interaction patterns of these predators is especially important in a scenario of worldwide defaunation. Body sizes of predators and their prey are related to biomechanical and energetic constraints that influence the likelihood and strength of trophic interactions. If these constraints govern interaction patterns, body mass ratios should be good predictors of interaction frequencies in natural systems. Here we investigated how good are body mass ratios as predictors of trophic interactions of Neotropical carnivores. We compiled the largest database on diets of terrestrial Carnivora species along the Neotropics, with 179 studies of 31 species. We selected nine predator species (six Felidae, two Canidae and one Procyonidae), for which the diet descriptor frequency of occurrence (FO, percentage of fecal samples that contain a specific prey) was available for at least six different sites. Using FO as a proxy for probability of consumption of prey, we tested the fit of statistical models where FO is a response variable and prey-predator body mass ratio, the predictor. We performed analyses at site, species and family levels to test how consistent are these relationships and investigate whether body-mass ratios are better predictors of diet for certain groups than for others.
Results/Conclusions
We found that, for a general model aiming to predict the diets of carnivores, predator-prey body mass ratio alone was a relatively good predictor (pseudo-R²=0.49). When we split the model between Felidae and non-Felidae predators, its performance increased considerably (pseudo-R²>0.70). Within Felidae, diets were well predicted for most species (pseudo-R²>0.73), and prey use distributions overlapped with the mode around similar body mass ratios, suggesting a consistent rule relating body mass ratios and diets. Among non-felids, diet was well predicted by body mass ratios for all species (pseudo-R²>0.85), but distributions were highly skewed towards proportionally small prey. Within species, we found considerable variation at the sites-level, but overall congruence between the predicted and observed FOs. These results suggest that there may be an universal rule between body mass ratios and FOs for carnivores in general. Such rule seems to become stronger within more phylogenetically cohesive groups. This is an evidence that factors linked to predators’ evolutionary history, not accounted for in the models, influence in trophic interactions. Within species, prey use is highly determined by body mass, but context dependence at the site level can break these relationships making diets harder to predict.