Functional diversity increases the resistance of a tritrophic food web to environmental changes

In the light of global climate change and biodiversity loss, understanding the role of functional diversity in the response of food webs to environmental change is growing ever more important. Using a tritrophic food web model, with a variable degree of functional diversity at each trophic level, we studied the role of functional diversity on the resistance of a system against press perturbations affecting either nutrient availability or the mortality of the species, which can be interpreted as effects of eutrophication and warming respectively. We compared food webs with different levels of functional diversity by investigating the species trait and biomass dynamics, the overall changes in the species standing biomass as measured by the warping distance, and the duration of the system transients after the onset of a perturbation (transition time). We found that higher functional diversity increased resistance since it buffered trophic cascading effects and delayed the onset of oscillatory behaviour caused by either bottom-up forcing via perturbations to nutrient concentration or top-down forcing via perturbations to mortality rate. This increased resistance emerged from a higher top-down control of the intermediate species on the basal species. Functional diversity also promoted a higher top biomass, in particular via a higher proportion of top selective species undergoing high mortality rates. Additionally, functional diversity had context-dependent effects on warping distances, and increased transition times. Overall, this study encourages accounting for functional diversity in future investigations about the response of multitrophic systems to global change and in management strategies.